P0171 System Too Lean (Bank 1)
What does P0171 mean?
P0171 — System Too Lean (Bank 1) (bank 1). This is an OBD-II diagnostic trouble code a scanner retrieves when your vehicle's computer detects system too lean (bank 1) on bank 1. The level of risk depends on how the vehicle is currently running and how long you've been driving with the light on.
Common causes of P0171
- Vacuum leak in the intake system
- Mass air flow sensor dirty or failing
- Weak or failing fuel pump or clogged fuel filter
- Clogged fuel injectors
- Faulty oxygen sensor reporting lean incorrectly
How to fix P0171
- Smoke test the intake system to locate vacuum leaks
- Clean or replace the MAF sensor and verify readings on an OBD-II scanner
- Check fuel pressure and volume at the rail
- Monitor fuel trim values (STFT/LTFT) with a scan tool to confirm the leak side
- Inspect and clean fuel injectors if fuel delivery is the cause