What this code means

The PCM detected that the upstream heated oxygen sensor on Bank 1 is not showing enough voltage variation during closed-loop fuel control. The sensor signal is too steady when it should be switching between rich and lean.

Symptoms

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

Common causes

• Lazy or contaminated O2 sensor
• Exhaust leak near sensor
• Vacuum leak affecting air/fuel ratio
• Fuel delivery issue

Diagnostic steps

1. Monitor O2 sensor waveform with scan tool
2. Check for exhaust leaks near sensor
3. Perform vacuum leak test
4. Test fuel pressure
5. Inspect O2 sensor for contamination

Repair notes

Replace upstream O2 sensor Bank 1. Check for exhaust and vacuum leaks.

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