P0400 - Exhaust Gas Recirculation Flow Malfunction
The exhaust gas recirculation (EGR) valve is vacuum controlled valve that regulates
the amount of exhaust gases that re-enter the cylinders. The powertrain control
module (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 were
insufficient or non-existent, this code is set.
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No symptoms will likely be noticed by the driver other than the MIL (malfunction
indicator lamp). However, non visible symptoms will be increased combustion
temperature and increased Nox emissions.
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 EGR
- Faulty EGR valve
Possible Solutions: Since EGR valve designs are different, no one test will suffice:
- Using a scan tool, operate the EGR valve with the engine running. If the
engine stumbles, the problem was likely intermittent wiring problem or intermittent
- 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 of
valve and cleaning of all ports will be required
- Checking of solenoid can only usually be done with a scan tool, because
most solenoids operate with a duty cycle of voltage, rather than constant
- Check all vacuum lines, hoses, etc for any damage
- Visually inspect the solenoid harness and the solenoid for damage
- Replace EGR valve
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