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Home / DTC / P0143 — O2 Sensor Circuit Low Voltage Bank 1 Sensor 3

P0143 — O2 Sensor Circuit Low Voltage Bank 1 Sensor 3

Detailed page for trouble code P0143.

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Code

P0143

Generic P — Powertrain

O2 Sensor Circuit Low Voltage Bank 1 Sensor 3

Brand: Generic
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty (worn, contaminated or failed) Bank 1 Sensor 3 oxygen sensor
  • Open or shorted signal wire (short to ground) or poor connector contact
  • Corroded or damaged harness/connector pins
  • Exhaust leak upstream of the sensor causing abnormal readings
  • Fuel system problems causing a persistently very lean condition (fuel pressure, injectors)
  • Sensor heater failure or insufficient sensor temperature (separate heater codes may be present)

Symptoms

  • Check Engine MIL illuminated (fault code stored)
  • Poor fuel economy or richer/leaner-than-normal fuel trims
  • Failed emissions/inspection test
  • Possible rough idle or reduced driveability if related fuel trim is severe
  • No obvious immediate symptoms other than MIL in some cases

What to check

  • Read and record stored DTC(s) and freeze frame data; note related O2/heater codes
  • Inspect sensor and connector for physical damage, contamination, or corrosion
  • Visually inspect wiring for chafing, heat damage, pin corrosion, or rodent damage
  • Check for exhaust leaks upstream of Bank 1 Sensor 3 (smoke test or visual inspection)
  • Use a scan tool to monitor live O2 sensor voltage and fuel trim values in closed and open loop
  • Backprobe the sensor signal with a DVM/oscilloscope to confirm voltage behavior while engine is running

Signal parameters

  • Typical narrowband O2 sensor output: ~0.1 V (lean) to ~0.9 V (rich); low-voltage condition usually < ~0.1–0.2 V
  • Bank 1 Sensor 3 (downstream in many setups) may show lower activity than upstream sensors — expected to be more stable; sudden low steady voltage indicates a problem
  • Heater circuit supply usually vehicle battery/regulator voltage when switched on; heater resistance varies by sensor type (consult OEM spec)
  • Oscilloscope: upstream sensors switch frequently; downstream (post-cat) should be more stable — persistent low-level flatline is a fault indicator

Diagnostic algorithm

  1. Verify and document DTC P0143 and any related codes. Note freeze frame data and readiness status.
  2. Perform a visual inspection of Bank 1 Sensor 3, connector and harness for damage, corrosion, contamination or exhaust leaks. Repair obvious issues.
  3. Using a scan tool, monitor the sensor’s signal voltage at idle and while revving. Confirm the signal is abnormally low and not switching as expected (or is a flatline).
  4. Backprobe the signal wire with a DVM/oscilloscope. Verify actual voltage against expected ranges. Check for short to ground by measuring continuity between signal wire and chassis ground with ignition off.
  5. Check heater circuit: measure voltage at connector with key on (or engine running as specified) and measure heater resistance between heater pins; compare to manufacturer spec. If heater circuit shows open/short, investigate wiring/fuse/relay. Note: heater faults often set separate codes (e.g., P0141).
  6. If wiring and heater circuits check good, clear codes and substitute or replace the sensor with a known-good unit, then test drive to confirm the code does not return.
  7. If new sensor fails or wiring tests are abnormal, trace and repair wiring harness to PCM, repair connectors or grounds, or replace harness as required.
  8. If sensor and wiring are good but low voltage persists and no wiring fault is found, evaluate fuel system (fuel pressure, injectors) and PCM functionality. Consider ECM replacement only after exhausting wiring and sensor checks.

Likely causes

  • Failed or contaminated O2 sensor (most common)
  • Damaged/shorted signal wire or poor connector
  • Exhaust leak upstream of Sensor 3
  • Insufficient sensor heater operation preventing proper sensor output

Fault status

⚠️ Status
PCM detected low voltage from oxygen sensor circuit — Bank 1 Sensor 3. The sensor output is below expected range.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours
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Code

P0143

GWM P — Powertrain

- Low oxygen circuit voltage (bank 1, sensor 3)

Brand: GWM
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty (worn, contaminated or failed) Bank 1 Sensor 3 oxygen sensor
  • Open or shorted signal wire (short to ground) or poor connector contact
  • Corroded or damaged harness/connector pins
  • Exhaust leak upstream of the sensor causing abnormal readings
  • Fuel system problems causing a persistently very lean condition (fuel pressure, injectors)
  • Sensor heater failure or insufficient sensor temperature (separate heater codes may be present)

Symptoms

  • Check Engine MIL illuminated (fault code stored)
  • Poor fuel economy or richer/leaner-than-normal fuel trims
  • Failed emissions/inspection test
  • Possible rough idle or reduced driveability if related fuel trim is severe
  • No obvious immediate symptoms other than MIL in some cases

What to check

  • Read and record stored DTC(s) and freeze frame data; note related O2/heater codes
  • Inspect sensor and connector for physical damage, contamination, or corrosion
  • Visually inspect wiring for chafing, heat damage, pin corrosion, or rodent damage
  • Check for exhaust leaks upstream of Bank 1 Sensor 3 (smoke test or visual inspection)
  • Use a scan tool to monitor live O2 sensor voltage and fuel trim values in closed and open loop
  • Backprobe the sensor signal with a DVM/oscilloscope to confirm voltage behavior while engine is running

Signal parameters

  • Typical narrowband O2 sensor output: ~0.1 V (lean) to ~0.9 V (rich); low-voltage condition usually < ~0.1–0.2 V
  • Bank 1 Sensor 3 (downstream in many setups) may show lower activity than upstream sensors — expected to be more stable; sudden low steady voltage indicates a problem
  • Heater circuit supply usually vehicle battery/regulator voltage when switched on; heater resistance varies by sensor type (consult OEM spec)
  • Oscilloscope: upstream sensors switch frequently; downstream (post-cat) should be more stable — persistent low-level flatline is a fault indicator

Diagnostic algorithm

  1. Verify and document DTC P0143 and any related codes. Note freeze frame data and readiness status.
  2. Perform a visual inspection of Bank 1 Sensor 3, connector and harness for damage, corrosion, contamination or exhaust leaks. Repair obvious issues.
  3. Using a scan tool, monitor the sensor’s signal voltage at idle and while revving. Confirm the signal is abnormally low and not switching as expected (or is a flatline).
  4. Backprobe the signal wire with a DVM/oscilloscope. Verify actual voltage against expected ranges. Check for short to ground by measuring continuity between signal wire and chassis ground with ignition off.
  5. Check heater circuit: measure voltage at connector with key on (or engine running as specified) and measure heater resistance between heater pins; compare to manufacturer spec. If heater circuit shows open/short, investigate wiring/fuse/relay. Note: heater faults often set separate codes (e.g., P0141).
  6. If wiring and heater circuits check good, clear codes and substitute or replace the sensor with a known-good unit, then test drive to confirm the code does not return.
  7. If new sensor fails or wiring tests are abnormal, trace and repair wiring harness to PCM, repair connectors or grounds, or replace harness as required.
  8. If sensor and wiring are good but low voltage persists and no wiring fault is found, evaluate fuel system (fuel pressure, injectors) and PCM functionality. Consider ECM replacement only after exhausting wiring and sensor checks.

Likely causes

  • Failed or contaminated O2 sensor (most common)
  • Damaged/shorted signal wire or poor connector
  • Exhaust leak upstream of Sensor 3
  • Insufficient sensor heater operation preventing proper sensor output

Fault status

⚠️ Status
PCM detected low voltage from oxygen sensor circuit — Bank 1 Sensor 3. The sensor output is below expected range.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours
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Code

P0143

HUMMER P — Powertrain

Heated Oxygen Sensor (HO2S) Circuit Low Voltage Bank 1 Sensor 3

Brand: HUMMER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty (worn, contaminated or failed) Bank 1 Sensor 3 oxygen sensor
  • Open or shorted signal wire (short to ground) or poor connector contact
  • Corroded or damaged harness/connector pins
  • Exhaust leak upstream of the sensor causing abnormal readings
  • Fuel system problems causing a persistently very lean condition (fuel pressure, injectors)
  • Sensor heater failure or insufficient sensor temperature (separate heater codes may be present)

Symptoms

  • Check Engine MIL illuminated (fault code stored)
  • Poor fuel economy or richer/leaner-than-normal fuel trims
  • Failed emissions/inspection test
  • Possible rough idle or reduced driveability if related fuel trim is severe
  • No obvious immediate symptoms other than MIL in some cases

What to check

  • Read and record stored DTC(s) and freeze frame data; note related O2/heater codes
  • Inspect sensor and connector for physical damage, contamination, or corrosion
  • Visually inspect wiring for chafing, heat damage, pin corrosion, or rodent damage
  • Check for exhaust leaks upstream of Bank 1 Sensor 3 (smoke test or visual inspection)
  • Use a scan tool to monitor live O2 sensor voltage and fuel trim values in closed and open loop
  • Backprobe the sensor signal with a DVM/oscilloscope to confirm voltage behavior while engine is running

Signal parameters

  • Typical narrowband O2 sensor output: ~0.1 V (lean) to ~0.9 V (rich); low-voltage condition usually < ~0.1–0.2 V
  • Bank 1 Sensor 3 (downstream in many setups) may show lower activity than upstream sensors — expected to be more stable; sudden low steady voltage indicates a problem
  • Heater circuit supply usually vehicle battery/regulator voltage when switched on; heater resistance varies by sensor type (consult OEM spec)
  • Oscilloscope: upstream sensors switch frequently; downstream (post-cat) should be more stable — persistent low-level flatline is a fault indicator

Diagnostic algorithm

  1. Verify and document DTC P0143 and any related codes. Note freeze frame data and readiness status.
  2. Perform a visual inspection of Bank 1 Sensor 3, connector and harness for damage, corrosion, contamination or exhaust leaks. Repair obvious issues.
  3. Using a scan tool, monitor the sensor’s signal voltage at idle and while revving. Confirm the signal is abnormally low and not switching as expected (or is a flatline).
  4. Backprobe the signal wire with a DVM/oscilloscope. Verify actual voltage against expected ranges. Check for short to ground by measuring continuity between signal wire and chassis ground with ignition off.
  5. Check heater circuit: measure voltage at connector with key on (or engine running as specified) and measure heater resistance between heater pins; compare to manufacturer spec. If heater circuit shows open/short, investigate wiring/fuse/relay. Note: heater faults often set separate codes (e.g., P0141).
  6. If wiring and heater circuits check good, clear codes and substitute or replace the sensor with a known-good unit, then test drive to confirm the code does not return.
  7. If new sensor fails or wiring tests are abnormal, trace and repair wiring harness to PCM, repair connectors or grounds, or replace harness as required.
  8. If sensor and wiring are good but low voltage persists and no wiring fault is found, evaluate fuel system (fuel pressure, injectors) and PCM functionality. Consider ECM replacement only after exhausting wiring and sensor checks.

Likely causes

  • Failed or contaminated O2 sensor (most common)
  • Damaged/shorted signal wire or poor connector
  • Exhaust leak upstream of Sensor 3
  • Insufficient sensor heater operation preventing proper sensor output

Fault status

⚠️ Status
PCM detected low voltage from oxygen sensor circuit — Bank 1 Sensor 3. The sensor output is below expected range.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours
Repair manuals

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Code

P0143

LAND ROVER P — Powertrain

Oxygen sensor - low voltage circuit. Bank 1 - sensor 3

Brand: LAND ROVER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty (worn, contaminated or failed) Bank 1 Sensor 3 oxygen sensor
  • Open or shorted signal wire (short to ground) or poor connector contact
  • Corroded or damaged harness/connector pins
  • Exhaust leak upstream of the sensor causing abnormal readings
  • Fuel system problems causing a persistently very lean condition (fuel pressure, injectors)
  • Sensor heater failure or insufficient sensor temperature (separate heater codes may be present)

Symptoms

  • Check Engine MIL illuminated (fault code stored)
  • Poor fuel economy or richer/leaner-than-normal fuel trims
  • Failed emissions/inspection test
  • Possible rough idle or reduced driveability if related fuel trim is severe
  • No obvious immediate symptoms other than MIL in some cases

What to check

  • Read and record stored DTC(s) and freeze frame data; note related O2/heater codes
  • Inspect sensor and connector for physical damage, contamination, or corrosion
  • Visually inspect wiring for chafing, heat damage, pin corrosion, or rodent damage
  • Check for exhaust leaks upstream of Bank 1 Sensor 3 (smoke test or visual inspection)
  • Use a scan tool to monitor live O2 sensor voltage and fuel trim values in closed and open loop
  • Backprobe the sensor signal with a DVM/oscilloscope to confirm voltage behavior while engine is running

Signal parameters

  • Typical narrowband O2 sensor output: ~0.1 V (lean) to ~0.9 V (rich); low-voltage condition usually < ~0.1–0.2 V
  • Bank 1 Sensor 3 (downstream in many setups) may show lower activity than upstream sensors — expected to be more stable; sudden low steady voltage indicates a problem
  • Heater circuit supply usually vehicle battery/regulator voltage when switched on; heater resistance varies by sensor type (consult OEM spec)
  • Oscilloscope: upstream sensors switch frequently; downstream (post-cat) should be more stable — persistent low-level flatline is a fault indicator

Diagnostic algorithm

  1. Verify and document DTC P0143 and any related codes. Note freeze frame data and readiness status.
  2. Perform a visual inspection of Bank 1 Sensor 3, connector and harness for damage, corrosion, contamination or exhaust leaks. Repair obvious issues.
  3. Using a scan tool, monitor the sensor’s signal voltage at idle and while revving. Confirm the signal is abnormally low and not switching as expected (or is a flatline).
  4. Backprobe the signal wire with a DVM/oscilloscope. Verify actual voltage against expected ranges. Check for short to ground by measuring continuity between signal wire and chassis ground with ignition off.
  5. Check heater circuit: measure voltage at connector with key on (or engine running as specified) and measure heater resistance between heater pins; compare to manufacturer spec. If heater circuit shows open/short, investigate wiring/fuse/relay. Note: heater faults often set separate codes (e.g., P0141).
  6. If wiring and heater circuits check good, clear codes and substitute or replace the sensor with a known-good unit, then test drive to confirm the code does not return.
  7. If new sensor fails or wiring tests are abnormal, trace and repair wiring harness to PCM, repair connectors or grounds, or replace harness as required.
  8. If sensor and wiring are good but low voltage persists and no wiring fault is found, evaluate fuel system (fuel pressure, injectors) and PCM functionality. Consider ECM replacement only after exhausting wiring and sensor checks.

Likely causes

  • Failed or contaminated O2 sensor (most common)
  • Damaged/shorted signal wire or poor connector
  • Exhaust leak upstream of Sensor 3
  • Insufficient sensor heater operation preventing proper sensor output

Fault status

⚠️ Status
PCM detected low voltage from oxygen sensor circuit — Bank 1 Sensor 3. The sensor output is below expected range.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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+100 karma for a short comment :)
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