Can I drive with code P0401?

In most cases yes, but have it fixed soon, because emissions rise and the engine may start to knock.

Is cleaning the EGR valve enough?

Often yes, if soot is the cause. If the valve or its control is faulty, it needs replacing. A mechanic finds out by testing the valve.

Will my car pass its MOT with code P0401?

In the UK, an engine management light that shows a fault is a major defect, so the car fails its MOT. This applies to most petrol cars first used from 1 July 2003 and diesel cars first used from 1 July 2008. Elsewhere in Europe it depends on your country’s inspection rules; the EU roadworthiness directive lists an OBD read-out showing a significant malfunction as a reason for failure on petrol cars. This fault also affects exhaust emissions, so the car may fail the emissions test as well. It is safer to have it fixed before the test.

P0401 Code: Insufficient EGR Flow – Causes & Advice

P0401 code: insufficient EGR flow

Fault code P0401 means less gas is flowing through the exhaust gas recirculation (EGR) system than the ECM requests. The system sends part of the exhaust gas back into the intake to lower combustion temperatures and nitrogen oxide emissions. Most often the EGR valve or its passages are blocked with soot.

Check P0401

When the code is set

The ECM opens the EGR valve and uses sensors, such as intake manifold pressure, air flow or temperature, to check whether the exhaust gas flow is what it expects. When it detects too little flow on two drives in a row, it turns on the check engine light.

Can I keep driving?

Have it checked soon

In most cases you can drive without major problems, but have the fault fixed soon. Driving for a long time with too little EGR flow raises emissions, and petrol engines can start to knock.

Symptoms

The check engine light is on, sometimes with no other symptoms.
Less power.
Knocking under load (petrol engines).
Rough idle.
High readings in an exhaust emissions test.

Common causes

An EGR valve or passages blocked with soot.
A blocked EGR cooler.
A faulty EGR control solenoid or vacuum valve.
A faulty sensor that measures EGR flow, or its hoses.
Damaged EGR valve wiring.

How to find the cause

A mechanic usually works like this:

Read all codes and freeze frame data.
At idle, open the EGR valve with a diagnostic tool; the engine should stumble noticeably.
Inspect the EGR valve and passages for soot.
Check the hoses, sensors and wiring of the EGR system.

Other ways the code is written

Scan tools and workshop printouts sometimes show the code with extra characters:

P040100

Related codes

Frequently asked questions

Evoca fault code diagnostics is an informational aid and does not replace a professional inspection of your vehicle. Only an inspection of the vehicle at a workshop can confirm the cause of a fault.

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