What this code means

The PCM has detected that the front air-fuel ratio sensor is not performing within the expected range. The sensor output does not correctly correspond to the actual air-fuel ratio, affecting closed-loop fuel control accuracy.

Symptoms

• Check Engine Light
• Poor fuel economy
• Rough idle
• Hesitation on acceleration
• Failed emissions test

Common causes

• Contaminated A/F sensor from oil or coolant
• Aging A/F sensor with degraded performance
• Exhaust leak near sensor
• Fuel quality issue affecting sensor
• Incorrect sensor installed

Diagnostic steps

1. Monitor A/F sensor output on scan tool during various conditions
2. Check A/F sensor heater operation
3. Inspect for exhaust leaks near sensor
4. Check for oil or coolant contamination in exhaust
5. Compare sensor readings to known good values

Repair notes

Replace the front A/F sensor if its output does not match the expected range during testing.

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