Fault codes › Powertrain › Generic (SAE standard) › Fuel and air metering
P0171 Fuel system too lean (bank 1)
Needs attention Have it looked at soon. The car is usually driveable with care in the meantime.
What does P0171 mean?
P0171 is a generic powertrain code, defined by the SAE standard, so it means the same thing on every make and model: fuel system too lean (bank 1). It belongs to the fuel and air metering group of codes.
A control module stores the code when something it watches stays outside what it expects for long enough. On its own the code says which system complained, not which part has failed — the causes below, most likely first, are where to start.
Is it safe to drive with P0171?
Needs attention. Driveable gently. Sustained lean running overheats valves and the catalyst.
Common causes of P0171
- Unmetered air leak (intake or vacuum hose).
- Weak fuel pump or blocked filter.
- Dirty MAF sensor.
- Leaking exhaust before the oxygen sensor.
Symptoms
- Hesitation.
- Rough idle.
- Loss of power under load.
What to check first
- Smoke test for intake leaks.
- Fuel pressure.
- Fuel trim values at idle and load.
Can I just clear P0171?
You can, and the light goes out — but a fault that is still there sets the code again, often within a drive or two. Clearing also erases the freeze frame (what the engine was doing when the code was stored) and resets the emissions readiness monitors, so an MOT, smog or inspection test will wait until they have run again. Fix the cause first, then clear it, then watch whether it returns.
Read and clear P0171 from your iPhone with OBDTrip
Plug a Bluetooth OBD-II adapter into the car and OBDTrip reads every stored, pending and permanent code, explains each one in plain English like this, shows what the engine was doing when it was set, and clears the check engine light once the fault is fixed. It keeps a history of when each code comes back, and records every drive on its own from then on.
Needs a Bluetooth Low Energy adapter such as the Vgate iCar Pro — which adapters work with iPhone. Reading and clearing codes is part of an OBDTrip subscription.
Related codes
- P0100 Mass air flow circuit
- P0101 Mass air flow circuit range/performance
- P0102 Mass air flow circuit low input
- P0113 Intake air temperature circuit high input
- P0116 Coolant temperature circuit range/performance
- P0117 Coolant temperature circuit low input
General guidance from OBDTrip's fault-code catalogue, not a diagnosis of your car. When a code points to brakes, steering, overheating or a flashing check engine light, have the car looked at before driving on.