Code
P0431
Generic
P — Powertrain
Catalyst 1 Efficiency Below Threshold Bank 2
Views:
UK: 15
EN: 19
RU: 20
AI status
Completed
Completed
100%
Causes
- Aged or failed catalytic converter on Bank 2
- Faulty downstream oxygen sensor (Bank 2 Sensor 2) or upstream sensor (Bank 2 Sensor 1)
- Exhaust leak upstream of the downstream O2 sensor or at manifold gaskets
- Fuel mixture problems (lean or rich) caused by fuel system or vacuum leaks
- Ignition misfires or internal engine damage (excessive oil or coolant contamination)
- Damaged wiring, poor connectors, or heater circuit failure for O2 sensors
Symptoms
- Check Engine Light (MIL) illuminated
- Failed emissions or smog test
- Reduced fuel economy
- Sulfur/rotten-egg smell from the exhaust
- Occasional rough idle or hesitation if underlying ignition/fuel issues present
What to check
- Retrieve freeze frame and stored data with a scan tool; note pending/confirm counts
- Check for other codes (O2 sensor, misfire, fuel trim, EVAP) that may be related
- Visual inspection of exhaust system for leaks, damaged catalytic converter or heat shields
- Inspect wiring and connector condition for Bank 2 O2 sensors (S1 and S2) and heater circuits
- Compare live data: Bank 2 upstream (B2S1) and downstream (B2S2) O2 voltages and response
- Monitor short‑ and long‑term fuel trims and look for signs of lean or rich operation
Signal parameters
- B2S1 (upstream O2): switching between ~0.1–0.9 V under closed‑loop; frequency indicates proper catalyst feed
- B2S2 (downstream O2): should be relatively stable/less switching if converter is efficient (small amplitude ~0.1–0.4 V); if switching similar to B2S1, catalyst efficiency is low
- Oxygen sensor heater current/voltage and sensor heater fault flags
- Short term fuel trim (STFT) and long term fuel trim (LTFT) for Bank 2
- Catalyst temperature (if available) and delta between front and rear of converter
- Exhaust backpressure (kPa or inH2O) at idle and at higher RPM
Diagnostic algorithm
- Scan for codes and capture freeze frame. Note other related codes (O2 sensors, misfire, fuel trims).
- Clear codes and perform a monitored drive cycle to see if P0431 returns and under what conditions.
- Perform a careful visual inspection of the exhaust from manifold to tailpipe for leaks, holes, or damaged heat shields—repair any leaks and retest.
- Inspect connectors and wiring for Bank 2 O2 sensors; repair broken wires, corrosion, or poor grounds before replacing sensors.
- Using a scan tool, compare B2S1 and B2S2 voltages during steady cruise and snap throttle: a healthy cat will show B2S1 switching and B2S2 relatively steady; if B2S2 mirrors B2S1 the converter may be ineffective.
- Verify O2 sensor operation: check sensor heater power/ground, resistance where applicable, and response time. Substitute a known good sensor or use a lab scope if uncertain.
- Check fuel trims and perform cylinder balance or compression/ignition checks if misfires or fuel delivery issues are suspected. Correct fueling/ignition issues first, then retest catalyst efficiency.
- If catalytic converter plugging or internal damage is suspected, measure exhaust backpressure and/or temperature difference across the converter (front vs rear). A good converter normally runs hotter at the outlet.
- If tests confirm sensor wiring and engine are healthy but B2S2 behavior indicates low efficiency, replacement of the catalytic converter (or damaged component) may be required. Replace only after eliminating upstream causes.
- After repair, clear codes and perform a complete drive cycle or readiness test to verify the repair. Recheck for return of the code.
Likely causes
- Degraded/contaminated catalytic converter due to age or engine issues
- Bad Bank 2 downstream O2 sensor giving incorrect/slow readings
- Exhaust leak between the engine and the downstream sensor causing false low efficiency
- Persistent fuel trim issues (long‑term fuel trim showing rich/lean conditions)
- Intermittent misfires dumping unburned fuel into the cat and damaging it
Fault status
Status
Catalyst 1 Efficiency Below Threshold Bank 2 (P0431): Onboard diagnostics indicate the catalytic converter on bank 2 is not meeting efficiency thresholds. Possible causes include a failed converter, downstream O2 sensor fault, exhaust leak, fueling or ignition problems, or wiring/ECM issues. Further testing required.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P0431
GWM
P — Powertrain
- Catalyst performance is too low during warm-up (bank 2)
Views:
UK: 0
EN: 0
RU: 0
AI status
Completed
Completed
100%
Causes
- Aged or failed catalytic converter on Bank 2
- Faulty downstream oxygen sensor (Bank 2 Sensor 2) or upstream sensor (Bank 2 Sensor 1)
- Exhaust leak upstream of the downstream O2 sensor or at manifold gaskets
- Fuel mixture problems (lean or rich) caused by fuel system or vacuum leaks
- Ignition misfires or internal engine damage (excessive oil or coolant contamination)
- Damaged wiring, poor connectors, or heater circuit failure for O2 sensors
Symptoms
- Check Engine Light (MIL) illuminated
- Failed emissions or smog test
- Reduced fuel economy
- Sulfur/rotten-egg smell from the exhaust
- Occasional rough idle or hesitation if underlying ignition/fuel issues present
What to check
- Retrieve freeze frame and stored data with a scan tool; note pending/confirm counts
- Check for other codes (O2 sensor, misfire, fuel trim, EVAP) that may be related
- Visual inspection of exhaust system for leaks, damaged catalytic converter or heat shields
- Inspect wiring and connector condition for Bank 2 O2 sensors (S1 and S2) and heater circuits
- Compare live data: Bank 2 upstream (B2S1) and downstream (B2S2) O2 voltages and response
- Monitor short‑ and long‑term fuel trims and look for signs of lean or rich operation
Signal parameters
- B2S1 (upstream O2): switching between ~0.1–0.9 V under closed‑loop; frequency indicates proper catalyst feed
- B2S2 (downstream O2): should be relatively stable/less switching if converter is efficient (small amplitude ~0.1–0.4 V); if switching similar to B2S1, catalyst efficiency is low
- Oxygen sensor heater current/voltage and sensor heater fault flags
- Short term fuel trim (STFT) and long term fuel trim (LTFT) for Bank 2
- Catalyst temperature (if available) and delta between front and rear of converter
- Exhaust backpressure (kPa or inH2O) at idle and at higher RPM
Diagnostic algorithm
- Scan for codes and capture freeze frame. Note other related codes (O2 sensors, misfire, fuel trims).
- Clear codes and perform a monitored drive cycle to see if P0431 returns and under what conditions.
- Perform a careful visual inspection of the exhaust from manifold to tailpipe for leaks, holes, or damaged heat shields—repair any leaks and retest.
- Inspect connectors and wiring for Bank 2 O2 sensors; repair broken wires, corrosion, or poor grounds before replacing sensors.
- Using a scan tool, compare B2S1 and B2S2 voltages during steady cruise and snap throttle: a healthy cat will show B2S1 switching and B2S2 relatively steady; if B2S2 mirrors B2S1 the converter may be ineffective.
- Verify O2 sensor operation: check sensor heater power/ground, resistance where applicable, and response time. Substitute a known good sensor or use a lab scope if uncertain.
- Check fuel trims and perform cylinder balance or compression/ignition checks if misfires or fuel delivery issues are suspected. Correct fueling/ignition issues first, then retest catalyst efficiency.
- If catalytic converter plugging or internal damage is suspected, measure exhaust backpressure and/or temperature difference across the converter (front vs rear). A good converter normally runs hotter at the outlet.
- If tests confirm sensor wiring and engine are healthy but B2S2 behavior indicates low efficiency, replacement of the catalytic converter (or damaged component) may be required. Replace only after eliminating upstream causes.
- After repair, clear codes and perform a complete drive cycle or readiness test to verify the repair. Recheck for return of the code.
Likely causes
- Degraded/contaminated catalytic converter due to age or engine issues
- Bad Bank 2 downstream O2 sensor giving incorrect/slow readings
- Exhaust leak between the engine and the downstream sensor causing false low efficiency
- Persistent fuel trim issues (long‑term fuel trim showing rich/lean conditions)
- Intermittent misfires dumping unburned fuel into the cat and damaging it
Fault status
Status
Catalyst 1 Efficiency Below Threshold Bank 2 (P0431): Onboard diagnostics indicate the catalytic converter on bank 2 is not meeting efficiency thresholds. Possible causes include a failed converter, downstream O2 sensor fault, exhaust leak, fueling or ignition problems, or wiring/ECM issues. Further testing required.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
Similar codes
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Code
P0431
HUMMER
P — Powertrain
Warm Up Catalyst Efficiency Below Threshold (Bank 2)
Views:
UK: 6
EN: 15
RU: 10
AI status
Completed
Completed
100%
Causes
- Aged or failed catalytic converter on Bank 2
- Faulty downstream oxygen sensor (Bank 2 Sensor 2) or upstream sensor (Bank 2 Sensor 1)
- Exhaust leak upstream of the downstream O2 sensor or at manifold gaskets
- Fuel mixture problems (lean or rich) caused by fuel system or vacuum leaks
- Ignition misfires or internal engine damage (excessive oil or coolant contamination)
- Damaged wiring, poor connectors, or heater circuit failure for O2 sensors
Symptoms
- Check Engine Light (MIL) illuminated
- Failed emissions or smog test
- Reduced fuel economy
- Sulfur/rotten-egg smell from the exhaust
- Occasional rough idle or hesitation if underlying ignition/fuel issues present
What to check
- Retrieve freeze frame and stored data with a scan tool; note pending/confirm counts
- Check for other codes (O2 sensor, misfire, fuel trim, EVAP) that may be related
- Visual inspection of exhaust system for leaks, damaged catalytic converter or heat shields
- Inspect wiring and connector condition for Bank 2 O2 sensors (S1 and S2) and heater circuits
- Compare live data: Bank 2 upstream (B2S1) and downstream (B2S2) O2 voltages and response
- Monitor short‑ and long‑term fuel trims and look for signs of lean or rich operation
Signal parameters
- B2S1 (upstream O2): switching between ~0.1–0.9 V under closed‑loop; frequency indicates proper catalyst feed
- B2S2 (downstream O2): should be relatively stable/less switching if converter is efficient (small amplitude ~0.1–0.4 V); if switching similar to B2S1, catalyst efficiency is low
- Oxygen sensor heater current/voltage and sensor heater fault flags
- Short term fuel trim (STFT) and long term fuel trim (LTFT) for Bank 2
- Catalyst temperature (if available) and delta between front and rear of converter
- Exhaust backpressure (kPa or inH2O) at idle and at higher RPM
Diagnostic algorithm
- Scan for codes and capture freeze frame. Note other related codes (O2 sensors, misfire, fuel trims).
- Clear codes and perform a monitored drive cycle to see if P0431 returns and under what conditions.
- Perform a careful visual inspection of the exhaust from manifold to tailpipe for leaks, holes, or damaged heat shields—repair any leaks and retest.
- Inspect connectors and wiring for Bank 2 O2 sensors; repair broken wires, corrosion, or poor grounds before replacing sensors.
- Using a scan tool, compare B2S1 and B2S2 voltages during steady cruise and snap throttle: a healthy cat will show B2S1 switching and B2S2 relatively steady; if B2S2 mirrors B2S1 the converter may be ineffective.
- Verify O2 sensor operation: check sensor heater power/ground, resistance where applicable, and response time. Substitute a known good sensor or use a lab scope if uncertain.
- Check fuel trims and perform cylinder balance or compression/ignition checks if misfires or fuel delivery issues are suspected. Correct fueling/ignition issues first, then retest catalyst efficiency.
- If catalytic converter plugging or internal damage is suspected, measure exhaust backpressure and/or temperature difference across the converter (front vs rear). A good converter normally runs hotter at the outlet.
- If tests confirm sensor wiring and engine are healthy but B2S2 behavior indicates low efficiency, replacement of the catalytic converter (or damaged component) may be required. Replace only after eliminating upstream causes.
- After repair, clear codes and perform a complete drive cycle or readiness test to verify the repair. Recheck for return of the code.
Likely causes
- Degraded/contaminated catalytic converter due to age or engine issues
- Bad Bank 2 downstream O2 sensor giving incorrect/slow readings
- Exhaust leak between the engine and the downstream sensor causing false low efficiency
- Persistent fuel trim issues (long‑term fuel trim showing rich/lean conditions)
- Intermittent misfires dumping unburned fuel into the cat and damaging it
Fault status
Status
Catalyst 1 Efficiency Below Threshold Bank 2 (P0431): Onboard diagnostics indicate the catalytic converter on bank 2 is not meeting efficiency thresholds. Possible causes include a failed converter, downstream O2 sensor fault, exhaust leak, fueling or ignition problems, or wiring/ECM issues. Further testing required.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
P0431
MITSUBISHI
P — Powertrain
Warm up catalyst deterioration 2
Views:
UK: 5
EN: 10
RU: 7
AI status
Completed
Completed
100%
Causes
- Aged or failed catalytic converter on Bank 2
- Faulty downstream oxygen sensor (Bank 2 Sensor 2) or upstream sensor (Bank 2 Sensor 1)
- Exhaust leak upstream of the downstream O2 sensor or at manifold gaskets
- Fuel mixture problems (lean or rich) caused by fuel system or vacuum leaks
- Ignition misfires or internal engine damage (excessive oil or coolant contamination)
- Damaged wiring, poor connectors, or heater circuit failure for O2 sensors
Symptoms
- Check Engine Light (MIL) illuminated
- Failed emissions or smog test
- Reduced fuel economy
- Sulfur/rotten-egg smell from the exhaust
- Occasional rough idle or hesitation if underlying ignition/fuel issues present
What to check
- Retrieve freeze frame and stored data with a scan tool; note pending/confirm counts
- Check for other codes (O2 sensor, misfire, fuel trim, EVAP) that may be related
- Visual inspection of exhaust system for leaks, damaged catalytic converter or heat shields
- Inspect wiring and connector condition for Bank 2 O2 sensors (S1 and S2) and heater circuits
- Compare live data: Bank 2 upstream (B2S1) and downstream (B2S2) O2 voltages and response
- Monitor short‑ and long‑term fuel trims and look for signs of lean or rich operation
Signal parameters
- B2S1 (upstream O2): switching between ~0.1–0.9 V under closed‑loop; frequency indicates proper catalyst feed
- B2S2 (downstream O2): should be relatively stable/less switching if converter is efficient (small amplitude ~0.1–0.4 V); if switching similar to B2S1, catalyst efficiency is low
- Oxygen sensor heater current/voltage and sensor heater fault flags
- Short term fuel trim (STFT) and long term fuel trim (LTFT) for Bank 2
- Catalyst temperature (if available) and delta between front and rear of converter
- Exhaust backpressure (kPa or inH2O) at idle and at higher RPM
Diagnostic algorithm
- Scan for codes and capture freeze frame. Note other related codes (O2 sensors, misfire, fuel trims).
- Clear codes and perform a monitored drive cycle to see if P0431 returns and under what conditions.
- Perform a careful visual inspection of the exhaust from manifold to tailpipe for leaks, holes, or damaged heat shields—repair any leaks and retest.
- Inspect connectors and wiring for Bank 2 O2 sensors; repair broken wires, corrosion, or poor grounds before replacing sensors.
- Using a scan tool, compare B2S1 and B2S2 voltages during steady cruise and snap throttle: a healthy cat will show B2S1 switching and B2S2 relatively steady; if B2S2 mirrors B2S1 the converter may be ineffective.
- Verify O2 sensor operation: check sensor heater power/ground, resistance where applicable, and response time. Substitute a known good sensor or use a lab scope if uncertain.
- Check fuel trims and perform cylinder balance or compression/ignition checks if misfires or fuel delivery issues are suspected. Correct fueling/ignition issues first, then retest catalyst efficiency.
- If catalytic converter plugging or internal damage is suspected, measure exhaust backpressure and/or temperature difference across the converter (front vs rear). A good converter normally runs hotter at the outlet.
- If tests confirm sensor wiring and engine are healthy but B2S2 behavior indicates low efficiency, replacement of the catalytic converter (or damaged component) may be required. Replace only after eliminating upstream causes.
- After repair, clear codes and perform a complete drive cycle or readiness test to verify the repair. Recheck for return of the code.
Likely causes
- Degraded/contaminated catalytic converter due to age or engine issues
- Bad Bank 2 downstream O2 sensor giving incorrect/slow readings
- Exhaust leak between the engine and the downstream sensor causing false low efficiency
- Persistent fuel trim issues (long‑term fuel trim showing rich/lean conditions)
- Intermittent misfires dumping unburned fuel into the cat and damaging it
Fault status
Status
Catalyst 1 Efficiency Below Threshold Bank 2 (P0431): Onboard diagnostics indicate the catalytic converter on bank 2 is not meeting efficiency thresholds. Possible causes include a failed converter, downstream O2 sensor fault, exhaust leak, fueling or ignition problems, or wiring/ECM issues. Further testing required.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email