Fault P0400

Diagnostic trouble code (DTC) P0400 code stands for “Exhaust Gas Recirculation (EGR) Flow Malfunction.”

The code is logged once the flow of exhaust gas recirculation is lower than what the powertrain control module (PCM) expects.

Aside from the check engine light, you’ll usually experience engine hesitation, rough idling, reduced power, poor acceleration, engine knocking (or detonation), and poor fuel economy.

If the PCM detects that there is insufficient exhaust gas being sent into the engine, code P0400 will be triggered. This means that the system is not recirculating exhaust gas under conditions that require EGR.

Common causes are as follows:

1. Carbon build up causing the EGR valve to become stuck

2. Electronically or mechanically failed EGR valve

3. Damaged wiring

4. Dirty or faulty air flow sensor

5. EGR blanking plate fitted

6. Damaged or faulty EGR temperature or pressure sensor

7. Blocked or restricted intake manifold

Different manufacturers can often label P0400 as the following:

·        EGR valve stuck

·        EGR insufficient flow

·        EGR valve malfunction

Most common causes:

Often due to the nature of the EGR system, carbon will build up around the valve causing it to become jammed and this is the most likely cause.

EGR blanking plate has been fitted, often a 7mm hole is required in the blanking plate to allow partial flow to be seen by the ecu.

Dirty air flow sensor, as it is this sensor that measures the air being consumed by the engine and when a certain % of EGR gas is requested the ecu expects to see this amount of EGR gas subtracted from the total air consumption value.

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