P0401 on a GMC: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

Safe to drive, but the EGR problem can cause rough idle and an emissions test failure, so schedule the repair soon.

What P0401 means on a GMC

On a GMC, P0401 means the engine computer detected too little exhaust gas flowing through the EGR system. On GMC Vortec engines, carbon from the exhaust cakes onto the EGR valve and clogs the passages in the intake manifold, cutting EGR flow below the expected amount.

Is P0401 common on GMCs?

P0401 is common on higher-mileage GMC Sierra, Yukon, and Acadia models with Vortec V6 or V8 engines. The EGR valve and its intake passages are the usual failure points on this brand.

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

Symptoms

Check engine light is on
Rough or loping idle
Possible pinging under load
Failed emissions test for high NOx

Common causes

most common: EGR valve clogged with carbon
common: EGR passages in the intake manifold clogged with carbon
common: Faulty EGR position sensor
less common: Vacuum leak in the EGR line

How to fix it

Fix	DIY?	Typical cost
Clean the EGR valve and intake passages with intake cleaner	Yes	$15–60
Replace the EGR valve	Yes	$100–300
Have a shop decarbonize the intake and EGR system	Mechanic	$150–400