P0171
System Too Lean Bank 1
Powertrain · Generic (all makes)System: Intake Air/Vacuum + Fuel Delivery
Fix within days. Damage or fuel waste builds up.
Likely causes
- Vacuum leak (cracked hose, intake gasket, PCV)
- Dirty or failing mass air flow sensor
- Weak fuel pump or clogged fuel filter
- Exhaust leak ahead of the front oxygen sensor
What to check first
Smoke-test the intake for leaks first, then clean or test the MAF sensor and check fuel pressure.
Typical repair cost
$100 – $500
Independent-shop parts and labor for the usual fix. Your price depends on the actual cause and the vehicle.
Next step
General information, not a diagnosis of your vehicle. Repair costs are typical shop ranges, not quotes.