P0171 — Fuel System Too Lean Bank 1
Seen on: Heavy Truck/Diesel
Fuel System Too Lean Bank 1. Common causes: Clogged fuel filter or weak injectors.
Your code rides along, so nearby mechanics see the fault before they quote you.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Clogged fuel filter or weak injectors
- Vacuum leak
- MAF sensor fault
- low fuel pressure
First moves (roadside)
- Check fuel pressure
- inspect MAF sensor
- smoke-test for vacuum leaks
FAQ
Fuel System Too Lean Bank 1. Common causes: Clogged fuel filter or weak injectors.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Clogged fuel filter or weak injectors. Other possibilities include Vacuum leak; MAF sensor fault; low fuel pressure.
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Find a mechanic or related guides
General diagnostic guidance for diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack and more). Not a substitute for a scan-tool diagnosis on your specific truck.