System Diagnosis - Exhaust Gas Recirculation (EGR) System

EGR System Check:

EGR Valve Control Wiring Diagram:

Circuit Description:
The ECM operates a solenoid to control the exhaust gas recirculation (EGR) valve. This solenoid is normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass to the EGR valve. The ECM control of the EGR is based on the following inputs:

^ Engine coolant temperature - above 25°C

^ TPS - "OFF" idle

^ MAP

If Code 32 is stored, DTC 32 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. Checks for solenoid stuck open

2. Checks for solenoid always being energized

3. Grounding test terminal should energize solenoid and vacuum should drop

4. Negative backpressure valve should hold vacuum with engine "OFF"

5. When engine is started, exhaust backpressure should cause vacuum to bleed off and valve to fully close.


Diagnostic Aids:
Before replacing ECM, use an ohmmeter and check the resistance of each ECM controlled relay and solenoid coil. ECM QDR Check Procedure (Without 4L80-E Transmission) and ECM wiring diagram for coil terminal "ID" of solenoids and relays. Replace any solenoid where resistance measures less than 20 ohms.