Exhaust Gas Recirculation (EGR) Diagnosis

EGR System Check:

EGR System 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 monitors EGR effectiveness by de-energizing the EGR solenoid, thereby, shutting "OFF" vacuum to the EGR valve diaphragm. With the EGR valve closed and O2 sensor fluctuating normally, fuel integrator counts will be greater than they were during normal EGR operation. If the change is not within the calibrated window, a Code 32 will be set.

The ECM will check EGR operation when:
- Engine speed is above 2000 rpm.
- Engine vacuum is between 8 and 30 kPa (2" and 9" Hg).
- No change in throttle position while test is being performed.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. By grounding the diagnostic terminal, the EGR solenoid should be energized to allow vacuum to be 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 gauge 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. Negative backpressure EGR valve should hold vacuum with engine OFF.
5. When engine is started, exhaust backpressure should cause vacuum to bleed off and valve should fully close.

DIAGNOSTIC AIDS
Before replacing ECM use ohmmeter and check resistance of each ECM controlled relay and solenoid coil.
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.