Code
P0177
GWM
P — Powertrain
- Invalid indicator / not adjusted mixer sensor
AI status
Completed
Completed
100%
Causes
- Faulty mixture (AFR/lambda) sensor on Bank 2 (open/short or degraded element)
- Contaminated sensor (oil, coolant, soot)
- Damaged, corroded or loose wiring / connector to the sensor
- Heater circuit failure in the sensor
- Sensor installed incorrectly or not calibrated/initialized after replacement
- Vacuum or intake air leak affecting mixture reading
Symptoms
- Check Engine Light (MIL) illuminated
- Poor fuel economy
- Rough idle or uneven running
- Black exhaust smoke or rich-running symptoms
- Hesitation, stumbling or reduced performance
- Failed emission test
What to check
- Read freeze-frame data and DTC parameters with a scan tool; note conditions when code set
- Monitor live data: bank 2 mixture/AFR sensor output, bank 1 comparison, fuel trims (STFT/LTFT)
- Inspect sensor connector and wiring for corrosion, damage, or water ingress; wiggle test for intermittent faults
- Check sensor heater circuit resistance and power/ground presence with key on
- Perform intake vacuum/smoke test for leaks upstream of bank 2
- Check MAF/IAT readings and compare to expected values
Signal parameters
- Narrowband O2 (if fitted): switching voltage ~0.1–0.9 V, rapid oscillation around stoichiometric
- Wideband/AFR sensor (typical): manufacturer-specific; many output 0–5 V or sensor-specific current signal — consult vehicle wiring/repair manual
- Heater element typical cold resistance: commonly a few ohms to tens of ohms (refer to spec); no continuity or infinite resistance indicates heater fault
- Response time: sensor should respond quickly (
- Fuel trim behavior: large positive or negative LTFT/STFT on bank 2 indicates mixture control problem
Diagnostic algorithm
- Retrieve and record freeze-frame and live data for the code occurrence (engine load, RPM, temp, fuel trims, AFR/O2 outputs).
- Visually inspect bank 2 mixture sensor connector and wiring for damage, corrosion, pin push-out or water intrusion; repair any issues.
- With key ON, verify sensor heater circuit supply and ground; measure heater resistance and compare to spec. Replace sensor if heater is open or out of spec.
- Monitor sensor voltage/current at idle and under load. Compare to expected behavior and bank 1 sensor. If reading is flat, out-of-range or absent, suspect sensor or wiring.
- Check for intake vacuum leaks or exhaust leaks upstream of the sensor (smoke test). Repair leaks and clear codes.
- Check MAF and intake air measurements; clean or replace MAF if out of range. Re-check fuel trims.
- Test fuel pressure and inspect injectors for sticking/leaking. Correct any fuel delivery issues.
- If wiring and vehicle systems are good but readings remain out-of-range, replace the mixture/AFR sensor with an OEM-specified unit and perform required sensor adaptation/calibration procedures per manufacturer.
- After repairs, clear codes and perform a full drive cycle to confirm code does not return; re-check live data for proper operation.
- If code persists after sensor replacement and wiring repair, consider ECU/PCM diagnostic or software update as directed by manufacturer.
Likely causes
- Wiring/connectors (corrosion, damaged pins, intermittent connection)
- Failed or contaminated mixture (AFR/lambda) sensor
- Sensor heater circuit failure
- Unadjusted or incorrectly installed replacement sensor
- Intake leak or MAF fault producing incorrect AFR
- Excessive fuel pressure or leaking injector affecting local mixture
Fault status
Status
Invalid mixer/mixture sensor signal (Bank 2). ECM has detected an out-of-range or uninitialized mixture sensor input; sensor may be faulty, uncalibrated, or wiring/related systems may be causing incorrect readings.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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