OBD2 CodesApr 9, 20267 min read
P0171: System Too Lean Bank 1
Vacuum leaks, bad MAF sensor, or fuel delivery issues? Diagnose P0171 like a pro.
What is P0171?
The P0171 code means your engine is running too lean on Bank 1 - there's too much air or not enough fuel in the mixture.
Common Causes
- Vacuum Leaks - Most common cause
- Faulty MAF Sensor - Dirty or failing
- Weak Fuel Pump - Not delivering enough pressure
- Clogged Fuel Injectors
- Exhaust Leaks before O2 sensor
How to Diagnose
Check for Vacuum Leaks
- Listen for hissing sounds
- Spray carb cleaner around intake - RPM change indicates leak
- Inspect all vacuum hoses
Test MAF Sensor
- Check readings with scan tool
- Clean with MAF cleaner
- Replace if readings are off
Check Fuel System
- Test fuel pressure
- Inspect injector spray pattern
Fixes
- Replace vacuum hoses ($5-50)
- Clean or replace MAF ($20-150)
- Replace fuel filter or pump ($50-500)