Error code
OBD2 P0171
What it means
System Too Lean.
Severity
Summary
P0171 indicates a lean fuel mixture in engine bank 1, meaning there's too much air and not enough fuel.
Symptoms
- Stored trouble code and possibly an illuminated warning light
- Power loss or hesitation during acceleration
- Engine may stall unexpectedly at low speeds
- Rough idling with fluctuating idle speed
Common Causes
- Damaged vacuum lines, hoses, or inlet ducting
- Defective PCV valve
- Faulty MAF sensor
- Leaking intake manifold gaskets or seals
Diagnosis
- Check for additional codes and resolve them first
- Inspect vacuum lines, hoses, and inlet ducting for leaks
- Test the PCV valve and MAF sensor
- Examine intake manifold gaskets and seals
Fixes
- Replace damaged or leaking parts such as vacuum lines, hoses, PCV valves, and intake manifold gaskets/seals.
- Clean or replace the MAF sensor if it's faulty.
FAQ
Can bad gas cause lean code?
Bad fuel is unlikely to cause a lean condition; other issues like vacuum leaks are more common.
Can a dirty air filter cause a lean code?
A dirty air filter can restrict airflow but typically does not cause a lean condition. A clogged MAF sensor might be the issue instead.
Can spark plugs cause lean code?
Faulty spark plugs are unlikely to cause a lean condition; they affect ignition timing and combustion efficiency, not fuel mixture directly.
Can an exhaust leak cause a P0171 code?
An exhaust leak can introduce unmetered air into the intake system, causing a lean condition. Check for leaks in the vacuum lines or inlet ducting.
Can a bad O2 sensor cause P0171 code?
A faulty oxygen sensor might contribute to misdiagnosis but is unlikely to be the primary cause of a lean condition.
Can running lean damage an engine?
Running lean for extended periods can lead to poor performance and potential long-term wear on engine components.
Not affiliated with OBD2. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.
More OBD2 codes
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- P0102Mass or Volume Air Flow Circuit Low Input
- P0103Mass or Volume Air Flow Circuit High Input
- P0104Mass or Volume Air Flow Circuit Intermittent
- P0105Manifold Absolute Pressure/Barometric Pressure Circuit
- P0106Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance
- P0107Manifold Absolute Pressure/Barometric Pressure Circuit Low Input
- P0108Manifold Absolute Pressure/Barometric Pressure Circuit High Input
- P0109Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent
- P0110Intake Air Temperature Sensor 1 Circuit
- P0111Intake Air Temperature Sensor 1 Circuit Range/Performance