Question

2008 Mercury Mariner with engine code P0400, does it need to be fixed immediately?

Answer 1

Hi there,

This code is for the egr system and egr valve. It needs to be tested first to determine the cause of the code. Many times this code is caused by the DPFE sensor. This sensor measures the amount the egr is working. This will not harm the vehicle if it's not repaired right away, but you may encounter some running issues.