P0401 on a Subaru: 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 Subaru

On a Subaru, P0401 means the engine computer detected too little exhaust gas flowing through the EGR system. On Subaru 2.5L engines with an EGR system, carbon builds up in the valve and its intake passages until flow drops below the expected amount.

Is P0401 common on Subarus?

P0401 appears on higher-mileage Subaru Outback, Forester, and Legacy models with 2.5L engines. Carbon clogging in the EGR valve and passages is the typical cause, and cleaning the system usually resolves it.

Commonly reported on: Outback, Forester, Legacy, Impreza.

Symptoms

Check engine light is on
Rough idle
Possible hesitation during acceleration
Failed emissions test for high NOx

Common causes

most common: EGR passages clogged with carbon
common: EGR valve stuck closed by 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 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