P0400

DTC P0400 Exhaust Gas Recirculation (EGR) Error:

Exhaust Gas Recirculation (EGR) Error:

CIRCUIT DESCRIPTION
The Vehicle Control Module (VCM) operates a Electronic Vacuum Regulator Valve (EVRV) solenoid, which is pulse width modulated to control the Exhaust Gas Recirculation (EGR) valve. This solenoid is normally closed. By providing a ground path, the VCM energizes the solenoid which then allows vacuum to pass to the EGR valve. The VCM can vary solenoid "on-time" (duty cycle) from 0% to 100% for various engine load conditions.

The VCM monitors EGR effectiveness by de-energizing the EGR control solenoid, thereby, shutting "OFF" vacuum to the EGR valve diaphragm. With the EGR valve closed and oxygen sensor fluctuating normally, short term fuel trim counts will be greater than they were during normal EGR operation. If the test passed (EGR OK), it will only be run once per ignition cycle. If the test failed (EGR not OK), it must fail twice before DTC P0400 is set.

DTC PO400 WILL SET WHEN
The VCM monitors EGR effectiveness by de-energizing the EGR control solenoid, thereby, shutting "OFF" vacuum to the EGR valve diaphragm. With the EGR valve closed and oxygen sensor fluctuating normally, short term fuel trim counts will be greater than they were during normal EGR operation. If the test passed (EGR OK), it will only be run once per ignition cycle. If the test failed (EGR not OK), it must fail twice before DTC P0400 is set.
The VCM will check EGR operation when:
^ Vehicle is above 32 mph.
^ Engine vacuum is between 7.5 & 55 kPa (2 & 16 Hg).
^ Throttle Position (TP) angle between 10% and 25%.

ACTION TAKEN (VCM WILL DEFAULT TO)
No action taken.

DTC P0400 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 clear DTCs function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and Fuse #9 is removed for 10 seconds.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. With the ignition "ON," engine stopped, the solenoid should not be energized and vacuum should not pass to the EGR valve. Grounding the diagnostic terminal will energize the solenoid and allow vacuum to pass to valve.
2. Checks for plugged EGR passages. If passages are plugged, the engine may have severe detonation on acceleration.
3. The MIL (Service Engine Soon) should also flash while the diagnostic terminal is grounded. If the light does not flash, this may indicate that the "quad-driver" has been damaged.
4. The vehicle must be driven during this test in order to produce sufficient engine load to operate the EGR.
Lightly accelerating (approximately 1/4 throttle) will produce a large and stable enough reading to determine if the VCM is commanding the system "ON."

DIAGNOSTIC AIDS
Before replacing the VCM, use J39200 and check the resistance of each VCM controlled relay, solenoid coil, with the exception of the EVRV solenoid. The EVRV solenoid has solid state circuitry and can not be properly diagnosed with a resistance check.

Refer to Diagrams / Electrical for coil terminal identification of solenoid(s) and relay(s) to be checked. Electrical Diagrams

Replace any solenoid when resistance measures less than 20 ohms. Refer to Intermittents. - Intermittent Malfunctions