What this code means

The upstream O2 sensor voltage on Bank 1 is staying below 0.45V, indicating a lean condition or sensor fault.

Symptoms

• Check Engine Light
• Lean running
• Poor fuel economy
• Rough idle

Common causes

• Vacuum leak
• Faulty O2 sensor
• Exhaust leak before sensor
• Low fuel pressure
• Faulty fuel injector

Diagnostic steps

1. Check for vacuum leaks
2. Monitor O2 sensor voltage
3. Test fuel pressure
4. Perform smoke test on intake
5. Inspect O2 sensor

Repair notes

Fix vacuum or exhaust leak. Replace O2 sensor if confirmed faulty.

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