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P0171: System Too Lean (Bank 1)
Severity: Medium Drive gently and get it diagnosed soon.
What does P0171 mean?
The engine is getting too much air or too little fuel on bank 1, and the computer has reached the limit of how much fuel it can add to compensate.
Generic OBD-II definition: System Too Lean (Bank 1). Confirm applicability in your vehicle service information.
Common causes
- Vacuum leak (cracked hose, intake gasket, PCV valve)
- Dirty or faulty MAF sensor
- Weak fuel pump or clogged fuel filter
- Leaking exhaust before the upstream O2 sensor
Symptoms
- Rough or high idle
- Hesitation
- Possible misfires
Can I keep driving with P0171?
Severity: Medium Drive gently and get it diagnosed soon.
If the check engine light is flashing or the car runs badly, stop driving and have it checked.
Typical fixes
- Smoke-test the intake for vacuum leaks
- Clean the MAF sensor with MAF-specific cleaner
- Check fuel pressure
- Review fuel trim data with a scanner