What this code means

The upstream heated oxygen sensor on Bank 1 is not switching properly between rich and lean, and the adaptive fuel strategy has reached its correction limit. The PCM can no longer compensate for the condition.

Symptoms

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

Common causes

• Large vacuum leak
• Faulty HO2S sensor Bank 1
• Exhaust leak near sensor
• Fuel system issue (low pressure, leaking injector)
• MAF sensor malfunction

Diagnostic steps

1. Check for vacuum leaks with smoke test
2. Monitor O2 sensor switching on scan tool
3. Check fuel pressure
4. Inspect for exhaust leaks near O2 sensor
5. Check MAF sensor readings

Repair notes

Repair vacuum leaks. Replace O2 sensor if not switching. Check fuel system.

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