P0400 Exhaust Gas Recirculation Flow Malfunction

Description and meaning of DTC p0400

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles. Although generic, the specific repair steps may vary depending on make/model. The exhaust gas recirculation (EGR) valve is vacuum controlled valve that regulatesthe amount of exhaust gases that re-enter the cylinders. The powertrain controlmodule (PCM) determines how much based on engine load, temp, and other conditions. If the PCM detects that the amount of exhaust gases entering the cylinder wereinsufficient or non-existent, this code is set.

p0400 diagnostic trouble code symptoms

No symptoms will likely be noticed by the driver other than the MIL (malfunctionindicator lamp). However, non visible symptoms will be increased combustiontemperature and increased Nox emissions.

DTC p0400 - possible causes

A code P0400 may mean that one or more of the following has happened: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 EGRvalve Faulty EGR valve

How to fix OBD-II diagnostic trouble code p0400

Since EGR valve designs are different, no one test will suffice:Using a scan tool, operate the EGR valve with the engine running. If theengine stumbles, the problem was likely intermittent wiring problem or intermittentblockage problem If engine doesn't stumble, operate the EGR valve manually, if possible. If engine doesn't stumble and die, the ports are likely plugged. Removal ofvalve and cleaning of all ports will be required Checking of solenoid can only usually be done with a scan tool, becausemost solenoids operate with a duty cycle of voltage, rather than constantvoltageCheck all vacuum lines, hoses, etc for any damageVisually inspect the solenoid harness and the solenoid for damageReplace EGR valveRelated EGR codes: P0401, P0402, P0403, P0404, P0405, P0406, P0407, P0408, P0409

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