P0171 on a Ford: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

A Ford with P0171 is drivable short-term, but a lean mixture can cause misfires and should be fixed promptly.

What P0171 means on a Ford

On a Ford, P0171 means bank 1 is running lean — too much air or not enough fuel — and the PCM can't add enough fuel to correct it. Ford's computer uses the MAF sensor and oxygen sensors to judge the mixture, and when the correction hits its limit it sets P0171.

Is P0171 common on Fords?

P0171 is common on F-150s, Mustangs, Escapes, and Explorers with higher mileage. Vacuum leaks, dirty MAF sensors, and on EcoBoost engines, boost or PCV leaks are the usual causes.

Commonly reported on: F-150, Mustang, Escape, Explorer.

Symptoms

Check engine light on
Rough or surging idle
Hesitation under load
Worse fuel economy

Common causes

most common: Vacuum leak (intake boot, hoses, gaskets)
common: Dirty or failing MAF sensor
common: PCV system leak or bad valve
less common: Weak fuel pump or clogged fuel filter

How to fix it

Fix	DIY?	Typical cost
Inspect and repair vacuum leaks in the intake system	Yes	$10–150
Clean the MAF sensor with MAF cleaner	Yes	$10–20
Replace the PCV valve and hoses	Yes	$20–80
Replace a weak fuel pump or clogged fuel filter	Mechanic	$300–800