What this code means

The PCM has detected that the fuel control correction based on the Bank 1 upstream O2 sensor has reached its maximum limit. The PCM can no longer adequately compensate for the air-fuel ratio deviation.

Symptoms

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

Common causes

• Large vacuum leak
• Faulty upstream O2 sensor
• Exhaust leak before sensor
• Fuel pressure out of range
• MAF sensor malfunction

Diagnostic steps

1. Check fuel trim values on scan tool for direction of correction
2. Test for vacuum leaks
3. Monitor O2 sensor switching
4. Check fuel pressure
5. Inspect MAF sensor

Repair notes

Repair the underlying air-fuel ratio issue causing the control limit to be reached.

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