OBD code P0171

Bank 1 is running with too much air and not enough fuel, which can reduce power and raise combustion temperature.

Estimated severity

Medium

Common symptoms

Power loss, especially under acceleration
Hesitation at low load or when cold
Unstable idle in some cases
Higher fuel consumption despite the lean condition because of fuel corrections

Likely causes

Vacuum leaks in intake hoses or intake manifold
Dirty, out-of-calibration or faulty MAF sensor
Low fuel pressure from the pump, regulator or blocked filter
Partially clogged injectors
Exhaust leaks before the oxygen sensor

Recommended checks

1. Check whether related codes are present, such as MAF or oxygen sensor codes.
2. Visually inspect intake hoses and connections for cracks or loose clamps.
3. Clean the MAF sensor with a dedicated MAF cleaner if it is dirty.
4. Measure fuel pressure with a gauge and compare it with manufacturer specifications.
5. Check for exhaust leaks before the upstream oxygen sensor.

What does code P0171 mean?

Code P0171 means the ECU keeps adding fuel because it detects a lean condition on bank 1. Common causes include intake air leaks, a dirty MAF sensor or low fuel pressure. If left unresolved, it can lead to hesitation, overheating and possible valve or catalytic converter damage.

Try assisted diagnostics