What does P0171 System Too Lean (Bank 1) mean?
The P0171 code stands for "System Too Lean (Bank 1)".
This code indicates that the oxygen sensor in bank 1 of the engine has detected a lean condition, meaning there is too much oxygen in the exhaust.
Bank 1 refers to the side of the engine where cylinder #1 is located.
The code is triggered by the first downstream oxygen sensor and is one of the more common trouble codes.
Symptoms may include a lack of power, spark knock, rough idle, and hesitation/surge on acceleration.
Possible causes for this code include a dirty or faulty MAF (Mass Air Flow) sensor, vacuum leaks, a faulty oxygen sensor, and low fuel pressure.
Cleaning the MAF sensor and fixing any vacuum leaks are common solutions for this code.
P0171 Symptoms
- Lack of power
- Detonation (spark knock)
- Rough idle
- Hesitation/surge on acceleration
Possible P0171 Causes
- Dirty or faulty MAF sensor
- Vacuum leak downstream of MAF sensor
- Cracked vacuum or PCV line/connection
- Faulty or stuck open PCV valve
- Failed or faulty oxygen sensor (bank 1, sensor 1)
- Sticking/plugged or failed fuel injector
- Low fuel pressure (possible plugged/dirty fuel filter!)
- Exhaust leak between engine and first oxygen sensor
Troubleshooting P0171 error code
- Clean the MAF sensor
- Inspect vacuum and PCV hoses, replace/repair as required
- Inspect hoses and connections in the air intake system
- Inspect and test intake manifold gaskets for leakage
- Check for a dirty fuel filter and proper fuel pressure
- Monitor short and long term fuel trims using an advanced scan tool
- Run a smoke test (if available)
