P0171 on a GMC: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

Drivable for a short time, but a lean condition can cause misfires and rough running, so get it checked soon.

What P0171 means on a GMC

On a GMC, P0171 means bank 1 is running lean, so the engine is getting too much air or not enough fuel. The engine computer has already added as much fuel as it can and still sees a lean mixture, so it turns on the check engine light.

Is P0171 common on GMCs?

P0171 is common on GMC trucks and SUVs with the 4.8L, 5.3L, and 6.0L V8s, especially once they pass high mileage. Intake manifold gaskets and vacuum leaks let in unmetered air, and a dirty MAF is another frequent cause. Over-oiled performance air filters can also foul the MAF sensor.

Commonly reported on: Sierra, Yukon, Canyon, Acadia.

Symptoms

Check engine light on
Rough or surging idle
Hesitation under acceleration
Poor fuel economy

Common causes

most common: Vacuum leak from a cracked hose or gasket
common: Dirty or failing mass air flow (MAF) sensor
common: Leaking intake manifold gaskets on high-mileage V8s
less common: Clogged PCV valve or hose
less common: Weak fuel pump or clogged fuel filter

How to fix it

Fix	DIY?	Typical cost
Inspect and replace cracked vacuum hoses	Yes	$10–60
Clean the MAF sensor with MAF cleaner spray	Yes	$10–20
Replace leaking intake manifold gaskets	Mechanic	$200–600
Replace a weak fuel pump	Mechanic	$400–800