Exhaust Gas Recirculation: Testing and Inspection

Chart C-7C "Exhaust Gas Recirculation":

Wiring Diagram - Exhaust Gas Recirculation (EGR) Valve:

Circuit Description:

The Exhaust Gas Recirculation (EGR) valve is controlled by a normally open solenoid (allows vacuum to pass when de-energized). When the ECM energizes the solenoid by completing a ground circuit, the EGR is turned "OFF." The ECM controls EGR based on the following inputs:

Coolant temperature

Throttle position

Engine rpm

TCC state

Barometric pressure


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. This tests for restricted valve or passage in manifold. Engine should run roughly or stall as valve is opened manually.

2. EGR valve diaphragm should begin to move as the engine speed approaches 2000 rpm.

3. This test should result in the EGR solenoid being energized, shutting off vacuum to the EGR valve diaphragm. This indicates EGR system is functioning properly.

4. Vacuum below 23.6 kPa (7" Hg) at 2000 rpm is insufficient for proper EGR operation. Lower vacuum readings require repair.


5. With the ignition "ON" and engine stopped, the ECM normally grounds terminal "T" to energize the EGR solenoid. This step checks for a defective (always open) solenoid or an electrical circuit problem.

6. The EGR solenoid is normally de-energized with the engine idling at normal operating temperature. This step checks for a defect (always closed) solenoid or an electrical circuit problem.

7. This step determines whether ECM is providing ground to terminal "T" or CKT 435 is shorted to ground.

Diagnostic Aids:

Vacuum lines should be thoroughly checked for internal restrictions. If no problems are found, refer to "Intermittents" in DIAGNOSIS BY SYMPTOM.



Note: Because of the internal bleed valve in the positive backpressure EGR used on this engine the valve will not open by applying vacuum with the engine stopped or at idle.


**CEC