OBD-IIO2 Sensor / AFR
O2 Sensor / AFR Fault Codes
Oxygen sensor and air-fuel ratio sensor circuit and performance codes.
Diagnostic Approach — O2 Sensor / AFR
- 1
Verify which sensor is affected — upstream (Sensor 1) or downstream (Sensor 2).
- 2
Check heater circuit first — most O2 codes are heater circuit failures.
- 3
Monitor O2 sensor waveform with live data — upstream should switch rapidly.
- 4
Check for exhaust leaks near sensor bung — leaks cause false lean readings.
- 5
Test sensor resistance and heater circuit with DVOM before replacing.
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