What this code means

The upstream O2 sensor on Bank 1 is responding too slowly to fuel mixture changes.

Symptoms

• Check Engine Light
• Poor fuel economy
• Failed emissions test
• Slight hesitation

Common causes

• Aging O2 sensor
• Contaminated sensor (oil/coolant/fuel additives)
• Exhaust leak
• Wiring issue

Diagnostic steps

1. Monitor O2 sensor switching frequency (should be >6 switches in 10 sec)
2. Check for exhaust leaks
3. Inspect sensor for contamination
4. Test response to induced rich/lean

Repair notes

Replace O2 sensor. This is a common wear item.

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