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Question

What is the most likely cause when the diagnostic code P0401, "EGR (exhaust gas recirculation) flow insufficient" is retrieved during vehicle servicing?

Answer

A clogged EGR valve or tube is the most likely cause.

The P0401 diagnostic code being retrieved during vehicle servicing indicates a problem with the EGR system, which reduces emissions by recirculating a portion of the engine's exhaust gases into the combustion process. When the flow of recirculated exhaust gases is insufficient, it may be due to a clogged or restricted EGR valve or tube. This can lead to increased emissions and reduced fuel economy, so it should be addressed as soon as possible to prevent further damage to the vehicle.