P0401

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EGR Flow Insufficient

What this code means

The exhaust gas recirculation valve is not flowing enough exhaust back into the intake, usually due to carbon buildup.

Common symptoms

Check engine light
Pinging/knocking under acceleration
Rough idle in some cases

Most common causes

Carbon-clogged EGR valve or passages
Faulty EGR valve or position sensor
Blocked vacuum lines (older systems)

Can you keep driving?

Driveable, but engine knock under load can damage pistons over time - have the EGR cleaned or replaced soon.

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Descriptions are for guidance only. Accurate diagnosis requires a workshop inspection.