Exhaust Gas Recirculation: Testing and Inspection

- Chart C-7C EGR Valve Check.:

- Wiring Diagram for Chart C-7C EGR Valve Check.:

CHART C-7C EXHAUST GAS RECIRCULATION CHECK (VIN Y)

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 monitors EGR effectiveness by de-energizing the EGR control solenoid thereby shutting off vacuum to the EGR valve diaphragm. With the EGR valve closed, manifold vacuum will be greater than it was during normal EGR operation and this change will be relayed to the ECM by the MAP sensor. If the change is not within the calibrated window, a Code 53 will be set.
The ECM will check EGR operation when:
a. Vehicle speed is above 50 mph.
b. Engine vacuum is between 40 and 51 kPa.
c. No change in throttle position while test is being run.
d. TCC "ON"

Chart Description:
1. By grounding the diagnostic terminal, the EGR solenoid should be energized and allow vacuum to applied to the EGR valve and the vacuum should hold.
2. When the diagnostic terminal is ungrounded, the vacuum to the EGR valve should bleed off through a vent in the solenoid and the valve should close. The gage may or may not bleed off but this does not indicate a problem.
3. This test will determine if the electrical control part of the system is at fault or if the connector or solenoid is at fault.
4. This system uses a negative backpressure valve which should hold vacuum with engine "OFF".
5. If the test light goes "OFF" when ECM connector is disconnected, the ECM has to be replaced, as the quad driver inside the ECM is faulty.
6. When engine is started, exhaust backpressure should cause vacuum to bleed off and valve should fully close.

Diagnostic Aids:

Vacuum lines should be thoroughly checked for internal restrictions. The ECM uses the MAP sensor for checking EGR operation. If there is a question of MAP sensor accuracy use MAP output check.
If no problems are found, refer to Intermittent Section.(Diagnosis by symptom).