What the P0400 code means?
P0400 is an OBD-II generic code that the engine control module (ECM) detected the engine exhaust gas
recirculation (EGR) valve is not flowing recalculated exhaust gases when it is commanded to open the flow
of gases into the intake manifold.
What causes the P0400 code?
Plugged EGR passage which restricts the flow of exhaust gasses
Faulty EGR solenoid
Faulty EGR solenoid wiring/harness
Vacuum lines damaged/disconnected to the EGR valve solenoid or to the EGR valve
Faulty EGR valve
What are the symptoms of the P0400 code?
Check Engine Light will illuminate
In most cases, there are no adverse conditions noticed by the driver
In some cases, there may be performance problems, such as pinging on acceleration, when the engine is
under load or when driving the vehicle at higher speeds
Common mistakes when diagnosing the P0400 code
Replacing the EGR valve before checking for carbon build up on the EGR temperature sensor
Replacing the EGR valve without checking the EGR pressure transducer for proper function
What repairs can fix the P0400 code?
Replacing the EGR valve
Replacing a broken vacuum line to the EGR valve
Replacing an EGR temperature sensor or cleaning the carbon off of it to repair it
Cleaning carbon out of EGR tubes to intake manifold