Code
P1143
BUICK
P — Powertrain
HO2S Bank 1 Sensor 3 Lean Or Low Voltage
Views:
UK: 19
EN: 31
RU: 19
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
CADILLAC
P — Powertrain
HO2S Bank 1 Sensor 3 Lean Or Low Voltage
Views:
UK: 18
EN: 37
RU: 23
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
CHEVROLET
P — Powertrain
HO2S Bank 1 Sensor 3 Lean Or Low Voltage
Views:
UK: 19
EN: 28
RU: 21
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
CHRYSLER
P — Powertrain
HO2S Bank 1 Sensor 3 Lean Or Low Voltage
Views:
UK: 17
EN: 30
RU: 19
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
DAEWOO
P — Powertrain
FEED BACK SOL V/V MAL
Views:
UK: 2
EN: 3
RU: 4
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
GM
P — Powertrain
HO2S Bank 1 Sensor 3 Lean Or Low Voltage
Views:
UK: 17
EN: 31
RU: 20
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
GMC
P — Powertrain
HO2S Bank 1 Sensor 3 Lean Or Low Voltage
Views:
UK: 20
EN: 29
RU: 19
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
HUMMER
P — Powertrain
Heated Oxygen Sensor (HO2S) Bank 1 Sensor 3 Lean System or Low Voltage
Views:
UK: 11
EN: 12
RU: 12
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
JAGUAR
P — Powertrain
Air Assisted Injector Control Valve Range Performance
Views:
UK: 19
EN: 26
RU: 19
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
LAND ROVER
P — Powertrain
Range / performance of auxiliary air valve circuit
Views:
UK: 4
EN: 5
RU: 6
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
Similar codes
Workshop Manuals
Repair manuals for LAND ROVER
3
Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop ManualLand Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop ManualLand Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop ManualYour experience will help others
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Code
P1143
MAZDA
P — Powertrain
HO2S Bank 1 Sensor 3 Signal Below 0.45v AF Ratio Too Lean
Views:
UK: 21
EN: 29
RU: 21
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
MINI
P — Powertrain
Heated oxygen sensor (HO2S) 2, bank 1 - signal too high
Views:
UK: 6
EN: 2
RU: 5
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
OLDSMOBILE
P — Powertrain
HO2S Bank 1 Sensor 3 Lean Or Low Voltage
Views:
UK: 21
EN: 28
RU: 23
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
Other
P — Powertrain
Air Assist Control Valve Range/Performance
Views:
UK: 17
EN: 29
RU: 19
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Workshop ManualYour experience will help others
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Code
P1143
SATURN
P — Powertrain
HO2S Bank 1 Sensor 3 Lean Or Low Voltage
Views:
UK: 19
EN: 31
RU: 21
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
Similar codes
Your experience will help others
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Code
P1143
SUBARU
P — Powertrain
Pressure Sensor Circuit Low Input
Views:
UK: 19
EN: 31
RU: 26
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P1143
VOLKSWAGEN
P — Powertrain
Load Calculation Cross Check Upper Limit Exceeded
Views:
UK: 18
EN: 35
RU: 20
AI status
Completed
Completed
100%
Causes
- Open or short in sensor signal or ground wiring
- Poor connector connections or corrosion at the sensor connector
- Failed or contaminated HO2S (sensor element or heater)
- Exhaust leak upstream of the sensor
- Fuel delivery or air metering problem causing actual lean condition
- Catalytic converter or exhaust system fault allowing abnormal downstream readings
Symptoms
- MIL/Check Engine Light illuminated
- Possible reduced fuel economy or drivability issues if the PCM goes into open‑loop or trims are driven aggressively
- Rough idle or hesitation if underlying lean condition exists
- Possible failed emissions test
What to check
- Retrieve all stored codes and freeze frame/live data; note fuel trims, upstream HO2S behavior and sensor 3 voltage
- Visual inspection of exhaust and sensor wiring/connectors for damage, corrosion, or soot indicating leaks
- Backprobe or scope the sensor 3 signal while engine running and compare to upstream sensor voltage
- Check heater circuit operation: battery voltage at connector and heater resistance per service data
- Check for related issues that cause lean condition: fuel pressure, MAF, vacuum leaks, ignition misfires
- Perform smoke test for intake/exhaust leaks if lean running suspected
Signal parameters
- Narrowband oxygen sensor voltage range: ~0–1.0 V (switching). Downstream (sensor 3) typically shows a more stable value near ~0.4–0.6 V with small fluctuations when catalyst is effective
- Low/lean indication commonly seen as a sustained voltage below ~0.2 V (exact threshold varies by manufacturer)
- Heater circuit: heater supply should be battery voltage when commanded on; heater element resistance typically low (manufacturer-specific, commonly a few ohms to tens of ohms) — consult vehicle service data
Diagnostic algorithm
- Record freeze frame and all active/pending codes. Note short/long term fuel trims and upstream HO2S behavior.
- Perform a visual inspection of Bank 1 Sensor 3 connector and wiring for chafing, pin corrosion, rodent damage, or exhaust contact.
- With ignition off, unplug the sensor and inspect pins for corrosion or bent pins. Reconnect and ensure secure fit.
- With engine running, monitor Live Data: observe Bank 1 Sensor 1 (upstream) and Sensor 3 signals. If upstream switches and downstream is low/flat, suspect sensor or catalytic efficiency; if downstream mimics upstream, suspect catalyst inefficiency or sensor shorted.
- Measure sensor 3 signal voltage with a digital multimeter or oscilloscope. Look for sustained low voltage (< ~0.2 V) or no activity.
- Check heater circuit: verify heater supply voltage and ground, and measure heater resistance. Replace sensor if heater open or not powered as commanded.
- Check for exhaust leaks upstream of sensor 3 — perform smoke test or inspect flange/gasket and pipe joints.
- Verify fuel system and air metering: check fuel pressure, MAF sensor operation, and perform smoke/leak test for vacuum leaks if trims indicate lean condition.
- Inspect PCM grounds and connectors if wiring and sensor test good.
- If wiring, heater and system checks are normal but sensor signal remains low, replace the downstream HO2S (Bank 1 Sensor 3). After repairs clear codes and road test to confirm issue is resolved.
Likely causes
- Damaged frayed signal wire or pin pushed out of connector for Bank 1 Sensor 3
- Failed downstream oxygen sensor (heater or sensing element)
- Corroded/loose sensor connector or poor ground
- Exhaust leak between upstream and downstream sensors
- Low fuel pressure, MAF or vacuum leak causing lean running conditions
Fault status
Status
HO2S Bank 1 Sensor 3 lean or low voltage detected — low sensor voltage or biased lean reading on downstream oxygen sensor. Possible wiring, sensor, fuel/air, exhaust leak, or catalytic converter issue.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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