What does it mean?
P1165 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Lean A/F-11 (Bank 1 Sensor 1) Range/Performance .
Symptoms
- Check engine light on, sometimes with lean fuel trim codes alongside
- Rough or hunting idle that may stall when cold
- Hesitation and lack of power when accelerating
- Hissing or whistling noise from the intake area
- Higher fuel consumption as the module keeps adding fuel
- Occasional backfire on deceleration
Likely causes
- Unmetered air entering after the mass air flow sensor: cracked intake boot, loose clamp, split vacuum hose, leaking intake gasket
- Low fuel pressure or volume from a weak pump, clogged filter or restricted line
- Dirty, oil-fouled or failing mass air flow sensor under-reporting airflow
- Clogged or partly blocked injectors on bank 1
- Exhaust leak ahead of the sensor pulling in fresh air
- Stuck-open EVAP purge valve or a leaking crankcase ventilation system
- Drifted or contaminated air/fuel sensor reading falsely lean
How to fix it
- Read live fuel trims: high positive long term trim on bank 1 means genuine lean, near-zero trim points to a sensor or wiring fault
- Smoke test the intake system, vacuum hoses and crankcase ventilation plumbing to find unmetered air
- Measure fuel pressure with the engine running and under load; check the filter and pump delivery
- Clean or test the mass air flow sensor and compare its readings against expected airflow values
- Inspect the exhaust manifold and sensor bung for leaks
- Check the EVAP purge valve for leakage with the engine at idle
- If everything checks out mechanically, test the sensor with a controlled rich condition and replace it if it does not respond