P0401 on a Honda: 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 Honda

On a Honda, P0401 means the engine computer detected too little exhaust gas flowing through the EGR system. On Honda engines the EGR valve bolts to the intake manifold, and carbon from the exhaust collects on the valve and in the passages until flow drops below what the computer expects.

Is P0401 common on Hondas?

Honda Accord, Civic, CR-V, and Odyssey models with higher mileage commonly see P0401 as carbon builds up on the EGR valve and clogs the intake passages. The EGR valve itself, rather than the wiring or computer, is the usual culprit on this brand.

Commonly reported on: Accord, Civic, CR-V, Odyssey.

Symptoms

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

Common causes

most common: Carbon buildup clogging the EGR passages in the intake
common: EGR valve stuck closed by carbon
common: Faulty EGR valve position sensor
less common: Vacuum or wiring issue at the EGR valve

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	$120–350
Have a shop perform a professional decarbonization	Mechanic	$150–400