Symptoms of P0400 OBD II Trouble 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
Common Causes of P0400 OBD II Trouble Code
- 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
blockage 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 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
voltage
- Check all vacuum lines, hoses, etc for any damage
- Visually inspect the solenoid harness and the solenoid for damage
- Replace EGR valve