You are offline — AutoTools still works from your device.

Code

P0400

Emissions / EGR

EGR flow malfunction

The EGR flow is not as expected.

Search another code

Most likely causes

Clogged EGR valve
Blocked passages
Faulty valve

Symptoms you may notice

Check engine light
Rough idle
Spark knock

Checks to run

Inspect the EGR valve
Clean passages
Test the valve

Tools you may need

Socket set EGR cleaner

Always diagnose before replacing. Codes share symptoms; confirm the cause with measurements before buying parts.

Related codes in Emissions / EGR

EGR flow insufficient

EGR circuit malfunction

EGR sensor A circuit low

EGR valve range / performance

Ask the AI mechanic

Hi! Ask me anything about your car — codes, noises, parts, maintenance.