EGR System Check (Over 8500 GVW)

EGR System Flow Chart For 4.3L-S/T and 2.8L, 7.4L, 5.7L over 8500 GVW.:

EGR System Wiring For 4.3L-S/T and 2.8L, 7.4L, 5.7L, over 8500 GVW.:

EGR SYSTEM CHECK (OVER 8500 GVW)

Circuit Description:

The EGR valve is controlled by a normally closed solenoid (allows a vacuum to pass when energized). The ECM pulses the solenoid to turn "ON" and regulate the EGR. The ECM diagnoses the system using an internal EGR test procedure.

The ECM control of the EGR is based on the following inputs:

^ Engine coolant temperature - above 25~C.
^ TPS - "OFF" idle
^ MAP

If Code 24 is stored, use that chart first.

Code 32 will detect a faulty solenoid, vacuum supply, EGR Valve or plugged passage. This chart checks for plugged EGR passages, a sticking EGR valve, or a stuck open or inoperative solenoid.


Test Description: Numbers below refer to circled numbers 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.

2. Grounding the diagnostic terminal will energize the solenoid and allow vacuum to pass to valve.

3. Checks for plugged EGR passages. If passages are plugged, the engine may have severe detonation on acceleration.

4. The EGR solenoid will not be energized in Park or Neutral. This test will determine if the Park/Neutral switch input is being received by the ECM.


Diagnostic Aids:

^ Before replacing ECM use ohmmeter and check resistance of each ECM controlled relay and solenoid coil. Refer to ECM QDR Check under COMPUTERIZED ENGINE CONTROLS .

See ECM wiring diagram for coil terminal identification of solenoid(s) and relay(s) to be checked. Replace any relay or solenoid if the coil resistance measures less than 20 ohms.