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Home / DTC / P0139 — O2 Sensor Circuit Slow Response Bank 1 Sensor 2

P0139 — O2 Sensor Circuit Slow Response Bank 1 Sensor 2

Detailed page for trouble code P0139.

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22,491specific
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Code

P0139

Generic P — Powertrain

O2 Sensor Circuit Slow Response Bank 1 Sensor 2

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

Causes

  • Aging or contaminated downstream O2 sensor (Bank 1 Sensor 2)
  • Open, shorted or corroded wiring or connector to the sensor
  • Heater circuit failure in the O2 sensor (loss of sensor warm-up)
  • Exhaust leaks upstream of the sensor (allowing extra oxygen)
  • Contamination from coolant, oil, silicone, or fuel additives
  • Catalytic converter degraded or clogged (affecting downstream response)

Symptoms

  • Check Engine Light / MIL illuminated
  • Possible failed emissions test (high HC/CO)
  • Reduced fuel trim control accuracy; may affect fuel economy
  • No significant change in driveability in many cases
  • Occasional hesitation or rough idle if related faults exist

What to check

  • Read freeze frame and stored DTCs; look for related codes (upstream O2, heater circuits, fuel trim, catalytic converter)
  • Visual inspection of sensor, harness, and connector for damage, corrosion, or contamination
  • Check for exhaust leaks upstream of Bank 1 Sensor 2 (listen, feel, or smoke test with care)
  • Measure O2 sensor heater circuit resistance and supply voltage per vehicle spec
  • Compare live data: Bank 1 Sensor 1 (upstream) switching vs Bank 1 Sensor 2 response
  • Perform induced rich/lean stimulus (controlled snap throttle or propane) while monitoring downstream sensor response

Signal parameters

  • Typical narrowband O2 sensor voltage range: ~0.1–0.9 V (varies by sensor type)
  • Upstream sensor (Bank 1 Sensor 1) should switch rapidly between low (~0.1 V) and high (~0.8–0.9 V) under closed-loop conditions
  • Downstream sensor (Bank 1 Sensor 2) normally shows a more stable voltage reflecting catalytic converter efficiency; it should respond to upstream forced changes within a few hundred milliseconds
  • Heater circuit resistance commonly 2–20 ohms (vehicle-specific); heater supply voltage normally battery voltage when commanded on
  • Response time thresholds vary by manufacturer; a slow response is typically indicated when the downstream sensor response time is significantly longer than OEM spec

Diagnostic algorithm

  1. Confirm the code and record freeze-frame data. Scan for related codes (heater codes, upstream O2 codes, fuel trim or catalyst efficiency codes).
  2. Perform a visual inspection of Bank 1 Sensor 2, its harness and connector. Repair any damaged wiring or poor connections.
  3. Check for exhaust leaks upstream of the sensor and repair if present.
  4. With a multimeter, measure the heater circuit resistance and verify heater power/ground when key on/engine running; compare to vehicle spec.
  5. Using live-data (OBD-II scanner or scope), monitor Bank 1 Sensor 1 (upstream) and Bank 1 Sensor 2 signals during idle and during a controlled rich/lean stimulus (snap throttle or carefully introduce propane upstream).
  6. Evaluate response time: if upstream switches appropriately but downstream is slow to change, this indicates sensor slow response or catalytic converter damping. If downstream does not change at all, suspect wiring or sensor open/short.
  7. If wiring and heater are good but downstream response is slow, consider replacing Bank 1 Sensor 2. After replacement, clear codes and perform a test drive to verify the fault does not return.
  8. If replacement does not correct the issue, investigate catalytic converter efficiency (backpressure test, temperature tests, or catalyst monitoring results) and re-evaluate PCM/ECM operation.

Likely causes

  • Aged or contaminated downstream oxygen sensor
  • Heater element failure or poor sensor ground
  • Damaged wiring or bad connector corroded/loose
  • Exhaust leak between the engine and the sensor

Fault status

⚠️ Status
Bank 1 Sensor 2 (downstream O2 sensor) signal is responding slower than expected. Possible causes include a failing or contaminated sensor, heater or wiring issues, exhaust leak, or catalytic converter degradation. Further diagnosis is required before repair.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

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Code

P0139

GWM P — Powertrain

- The oxygen sensor (bank 1, sensor 2) responds with a delay,

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

Causes

  • Aging or contaminated downstream O2 sensor (Bank 1 Sensor 2)
  • Open, shorted or corroded wiring or connector to the sensor
  • Heater circuit failure in the O2 sensor (loss of sensor warm-up)
  • Exhaust leaks upstream of the sensor (allowing extra oxygen)
  • Contamination from coolant, oil, silicone, or fuel additives
  • Catalytic converter degraded or clogged (affecting downstream response)

Symptoms

  • Check Engine Light / MIL illuminated
  • Possible failed emissions test (high HC/CO)
  • Reduced fuel trim control accuracy; may affect fuel economy
  • No significant change in driveability in many cases
  • Occasional hesitation or rough idle if related faults exist

What to check

  • Read freeze frame and stored DTCs; look for related codes (upstream O2, heater circuits, fuel trim, catalytic converter)
  • Visual inspection of sensor, harness, and connector for damage, corrosion, or contamination
  • Check for exhaust leaks upstream of Bank 1 Sensor 2 (listen, feel, or smoke test with care)
  • Measure O2 sensor heater circuit resistance and supply voltage per vehicle spec
  • Compare live data: Bank 1 Sensor 1 (upstream) switching vs Bank 1 Sensor 2 response
  • Perform induced rich/lean stimulus (controlled snap throttle or propane) while monitoring downstream sensor response

Signal parameters

  • Typical narrowband O2 sensor voltage range: ~0.1–0.9 V (varies by sensor type)
  • Upstream sensor (Bank 1 Sensor 1) should switch rapidly between low (~0.1 V) and high (~0.8–0.9 V) under closed-loop conditions
  • Downstream sensor (Bank 1 Sensor 2) normally shows a more stable voltage reflecting catalytic converter efficiency; it should respond to upstream forced changes within a few hundred milliseconds
  • Heater circuit resistance commonly 2–20 ohms (vehicle-specific); heater supply voltage normally battery voltage when commanded on
  • Response time thresholds vary by manufacturer; a slow response is typically indicated when the downstream sensor response time is significantly longer than OEM spec

Diagnostic algorithm

  1. Confirm the code and record freeze-frame data. Scan for related codes (heater codes, upstream O2 codes, fuel trim or catalyst efficiency codes).
  2. Perform a visual inspection of Bank 1 Sensor 2, its harness and connector. Repair any damaged wiring or poor connections.
  3. Check for exhaust leaks upstream of the sensor and repair if present.
  4. With a multimeter, measure the heater circuit resistance and verify heater power/ground when key on/engine running; compare to vehicle spec.
  5. Using live-data (OBD-II scanner or scope), monitor Bank 1 Sensor 1 (upstream) and Bank 1 Sensor 2 signals during idle and during a controlled rich/lean stimulus (snap throttle or carefully introduce propane upstream).
  6. Evaluate response time: if upstream switches appropriately but downstream is slow to change, this indicates sensor slow response or catalytic converter damping. If downstream does not change at all, suspect wiring or sensor open/short.
  7. If wiring and heater are good but downstream response is slow, consider replacing Bank 1 Sensor 2. After replacement, clear codes and perform a test drive to verify the fault does not return.
  8. If replacement does not correct the issue, investigate catalytic converter efficiency (backpressure test, temperature tests, or catalyst monitoring results) and re-evaluate PCM/ECM operation.

Likely causes

  • Aged or contaminated downstream oxygen sensor
  • Heater element failure or poor sensor ground
  • Damaged wiring or bad connector corroded/loose
  • Exhaust leak between the engine and the sensor

Fault status

⚠️ Status
Bank 1 Sensor 2 (downstream O2 sensor) signal is responding slower than expected. Possible causes include a failing or contaminated sensor, heater or wiring issues, exhaust leak, or catalytic converter degradation. Further diagnosis is required before repair.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0138 P0135 P0159 P0171 P0420
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Code

P0139

HUMMER P — Powertrain

Heated Oxygen Sensor (HO2S) Slow Response Bank 1 Sensor 2

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

Causes

  • Aging or contaminated downstream O2 sensor (Bank 1 Sensor 2)
  • Open, shorted or corroded wiring or connector to the sensor
  • Heater circuit failure in the O2 sensor (loss of sensor warm-up)
  • Exhaust leaks upstream of the sensor (allowing extra oxygen)
  • Contamination from coolant, oil, silicone, or fuel additives
  • Catalytic converter degraded or clogged (affecting downstream response)

Symptoms

  • Check Engine Light / MIL illuminated
  • Possible failed emissions test (high HC/CO)
  • Reduced fuel trim control accuracy; may affect fuel economy
  • No significant change in driveability in many cases
  • Occasional hesitation or rough idle if related faults exist

What to check

  • Read freeze frame and stored DTCs; look for related codes (upstream O2, heater circuits, fuel trim, catalytic converter)
  • Visual inspection of sensor, harness, and connector for damage, corrosion, or contamination
  • Check for exhaust leaks upstream of Bank 1 Sensor 2 (listen, feel, or smoke test with care)
  • Measure O2 sensor heater circuit resistance and supply voltage per vehicle spec
  • Compare live data: Bank 1 Sensor 1 (upstream) switching vs Bank 1 Sensor 2 response
  • Perform induced rich/lean stimulus (controlled snap throttle or propane) while monitoring downstream sensor response

Signal parameters

  • Typical narrowband O2 sensor voltage range: ~0.1–0.9 V (varies by sensor type)
  • Upstream sensor (Bank 1 Sensor 1) should switch rapidly between low (~0.1 V) and high (~0.8–0.9 V) under closed-loop conditions
  • Downstream sensor (Bank 1 Sensor 2) normally shows a more stable voltage reflecting catalytic converter efficiency; it should respond to upstream forced changes within a few hundred milliseconds
  • Heater circuit resistance commonly 2–20 ohms (vehicle-specific); heater supply voltage normally battery voltage when commanded on
  • Response time thresholds vary by manufacturer; a slow response is typically indicated when the downstream sensor response time is significantly longer than OEM spec

Diagnostic algorithm

  1. Confirm the code and record freeze-frame data. Scan for related codes (heater codes, upstream O2 codes, fuel trim or catalyst efficiency codes).
  2. Perform a visual inspection of Bank 1 Sensor 2, its harness and connector. Repair any damaged wiring or poor connections.
  3. Check for exhaust leaks upstream of the sensor and repair if present.
  4. With a multimeter, measure the heater circuit resistance and verify heater power/ground when key on/engine running; compare to vehicle spec.
  5. Using live-data (OBD-II scanner or scope), monitor Bank 1 Sensor 1 (upstream) and Bank 1 Sensor 2 signals during idle and during a controlled rich/lean stimulus (snap throttle or carefully introduce propane upstream).
  6. Evaluate response time: if upstream switches appropriately but downstream is slow to change, this indicates sensor slow response or catalytic converter damping. If downstream does not change at all, suspect wiring or sensor open/short.
  7. If wiring and heater are good but downstream response is slow, consider replacing Bank 1 Sensor 2. After replacement, clear codes and perform a test drive to verify the fault does not return.
  8. If replacement does not correct the issue, investigate catalytic converter efficiency (backpressure test, temperature tests, or catalyst monitoring results) and re-evaluate PCM/ECM operation.

Likely causes

  • Aged or contaminated downstream oxygen sensor
  • Heater element failure or poor sensor ground
  • Damaged wiring or bad connector corroded/loose
  • Exhaust leak between the engine and the sensor

Fault status

⚠️ Status
Bank 1 Sensor 2 (downstream O2 sensor) signal is responding slower than expected. Possible causes include a failing or contaminated sensor, heater or wiring issues, exhaust leak, or catalytic converter degradation. Further diagnosis is required before repair.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0138 P0135 P0159 P0171 P0420
Repair manuals

Manual library for HUMMER

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Code

P0139

LAND ROVER P — Powertrain

Slow response from the heated oxygen sensor circuit - bank 1, sensor 2

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

Causes

  • Aging or contaminated downstream O2 sensor (Bank 1 Sensor 2)
  • Open, shorted or corroded wiring or connector to the sensor
  • Heater circuit failure in the O2 sensor (loss of sensor warm-up)
  • Exhaust leaks upstream of the sensor (allowing extra oxygen)
  • Contamination from coolant, oil, silicone, or fuel additives
  • Catalytic converter degraded or clogged (affecting downstream response)

Symptoms

  • Check Engine Light / MIL illuminated
  • Possible failed emissions test (high HC/CO)
  • Reduced fuel trim control accuracy; may affect fuel economy
  • No significant change in driveability in many cases
  • Occasional hesitation or rough idle if related faults exist

What to check

  • Read freeze frame and stored DTCs; look for related codes (upstream O2, heater circuits, fuel trim, catalytic converter)
  • Visual inspection of sensor, harness, and connector for damage, corrosion, or contamination
  • Check for exhaust leaks upstream of Bank 1 Sensor 2 (listen, feel, or smoke test with care)
  • Measure O2 sensor heater circuit resistance and supply voltage per vehicle spec
  • Compare live data: Bank 1 Sensor 1 (upstream) switching vs Bank 1 Sensor 2 response
  • Perform induced rich/lean stimulus (controlled snap throttle or propane) while monitoring downstream sensor response

Signal parameters

  • Typical narrowband O2 sensor voltage range: ~0.1–0.9 V (varies by sensor type)
  • Upstream sensor (Bank 1 Sensor 1) should switch rapidly between low (~0.1 V) and high (~0.8–0.9 V) under closed-loop conditions
  • Downstream sensor (Bank 1 Sensor 2) normally shows a more stable voltage reflecting catalytic converter efficiency; it should respond to upstream forced changes within a few hundred milliseconds
  • Heater circuit resistance commonly 2–20 ohms (vehicle-specific); heater supply voltage normally battery voltage when commanded on
  • Response time thresholds vary by manufacturer; a slow response is typically indicated when the downstream sensor response time is significantly longer than OEM spec

Diagnostic algorithm

  1. Confirm the code and record freeze-frame data. Scan for related codes (heater codes, upstream O2 codes, fuel trim or catalyst efficiency codes).
  2. Perform a visual inspection of Bank 1 Sensor 2, its harness and connector. Repair any damaged wiring or poor connections.
  3. Check for exhaust leaks upstream of the sensor and repair if present.
  4. With a multimeter, measure the heater circuit resistance and verify heater power/ground when key on/engine running; compare to vehicle spec.
  5. Using live-data (OBD-II scanner or scope), monitor Bank 1 Sensor 1 (upstream) and Bank 1 Sensor 2 signals during idle and during a controlled rich/lean stimulus (snap throttle or carefully introduce propane upstream).
  6. Evaluate response time: if upstream switches appropriately but downstream is slow to change, this indicates sensor slow response or catalytic converter damping. If downstream does not change at all, suspect wiring or sensor open/short.
  7. If wiring and heater are good but downstream response is slow, consider replacing Bank 1 Sensor 2. After replacement, clear codes and perform a test drive to verify the fault does not return.
  8. If replacement does not correct the issue, investigate catalytic converter efficiency (backpressure test, temperature tests, or catalyst monitoring results) and re-evaluate PCM/ECM operation.

Likely causes

  • Aged or contaminated downstream oxygen sensor
  • Heater element failure or poor sensor ground
  • Damaged wiring or bad connector corroded/loose
  • Exhaust leak between the engine and the sensor

Fault status

⚠️ Status
Bank 1 Sensor 2 (downstream O2 sensor) signal is responding slower than expected. Possible causes include a failing or contaminated sensor, heater or wiring issues, exhaust leak, or catalytic converter degradation. Further diagnosis is required before repair.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

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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 :)
Keep it short and practical. Up to 500 characters.
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Code

P0139

MITSUBISHI P — Powertrain

Oxygen sensor(rear) response

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

Causes

  • Aging or contaminated downstream O2 sensor (Bank 1 Sensor 2)
  • Open, shorted or corroded wiring or connector to the sensor
  • Heater circuit failure in the O2 sensor (loss of sensor warm-up)
  • Exhaust leaks upstream of the sensor (allowing extra oxygen)
  • Contamination from coolant, oil, silicone, or fuel additives
  • Catalytic converter degraded or clogged (affecting downstream response)

Symptoms

  • Check Engine Light / MIL illuminated
  • Possible failed emissions test (high HC/CO)
  • Reduced fuel trim control accuracy; may affect fuel economy
  • No significant change in driveability in many cases
  • Occasional hesitation or rough idle if related faults exist

What to check

  • Read freeze frame and stored DTCs; look for related codes (upstream O2, heater circuits, fuel trim, catalytic converter)
  • Visual inspection of sensor, harness, and connector for damage, corrosion, or contamination
  • Check for exhaust leaks upstream of Bank 1 Sensor 2 (listen, feel, or smoke test with care)
  • Measure O2 sensor heater circuit resistance and supply voltage per vehicle spec
  • Compare live data: Bank 1 Sensor 1 (upstream) switching vs Bank 1 Sensor 2 response
  • Perform induced rich/lean stimulus (controlled snap throttle or propane) while monitoring downstream sensor response

Signal parameters

  • Typical narrowband O2 sensor voltage range: ~0.1–0.9 V (varies by sensor type)
  • Upstream sensor (Bank 1 Sensor 1) should switch rapidly between low (~0.1 V) and high (~0.8–0.9 V) under closed-loop conditions
  • Downstream sensor (Bank 1 Sensor 2) normally shows a more stable voltage reflecting catalytic converter efficiency; it should respond to upstream forced changes within a few hundred milliseconds
  • Heater circuit resistance commonly 2–20 ohms (vehicle-specific); heater supply voltage normally battery voltage when commanded on
  • Response time thresholds vary by manufacturer; a slow response is typically indicated when the downstream sensor response time is significantly longer than OEM spec

Diagnostic algorithm

  1. Confirm the code and record freeze-frame data. Scan for related codes (heater codes, upstream O2 codes, fuel trim or catalyst efficiency codes).
  2. Perform a visual inspection of Bank 1 Sensor 2, its harness and connector. Repair any damaged wiring or poor connections.
  3. Check for exhaust leaks upstream of the sensor and repair if present.
  4. With a multimeter, measure the heater circuit resistance and verify heater power/ground when key on/engine running; compare to vehicle spec.
  5. Using live-data (OBD-II scanner or scope), monitor Bank 1 Sensor 1 (upstream) and Bank 1 Sensor 2 signals during idle and during a controlled rich/lean stimulus (snap throttle or carefully introduce propane upstream).
  6. Evaluate response time: if upstream switches appropriately but downstream is slow to change, this indicates sensor slow response or catalytic converter damping. If downstream does not change at all, suspect wiring or sensor open/short.
  7. If wiring and heater are good but downstream response is slow, consider replacing Bank 1 Sensor 2. After replacement, clear codes and perform a test drive to verify the fault does not return.
  8. If replacement does not correct the issue, investigate catalytic converter efficiency (backpressure test, temperature tests, or catalyst monitoring results) and re-evaluate PCM/ECM operation.

Likely causes

  • Aged or contaminated downstream oxygen sensor
  • Heater element failure or poor sensor ground
  • Damaged wiring or bad connector corroded/loose
  • Exhaust leak between the engine and the sensor

Fault status

⚠️ Status
Bank 1 Sensor 2 (downstream O2 sensor) signal is responding slower than expected. Possible causes include a failing or contaminated sensor, heater or wiring issues, exhaust leak, or catalytic converter degradation. Further diagnosis is required before repair.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0138 P0135 P0159 P0171 P0420
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

MITSUBISHI

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
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