Code
P1131
Fuel / Air
Oxygen sensor — bank 1, lean signal during closed loop
The engine is running lean in closed loop. Find the air or fuel issue first.
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Most likely causes
- Vacuum leak
- Weak fuel pressure
- Exhaust leak
- Faulty O2 sensor
Symptoms you may notice
- Check engine light
- Rough idle
- Poor economy
Checks to run
- Smoke test intake
- Check fuel pressure
- Inspect exhaust
Tools you may need
Smoke machine
Fuel pressure gauge
Always diagnose before replacing. Codes share symptoms; confirm the cause with measurements before buying parts.