With 4L80-E Automatic Transmission

EGR System Check:

EGR Control Solenoid Wiring Diagram:

Circuit Description:
The PCM operates a solenoid to control the Exhaust Gas Recirculation (EGR) valve. This solenoid is normally closed. By providing a ground path, the PCM energizes the solenoid which then allows vacuum to pass to the EGR valve.

The PCM monitors EGR effectiveness by de-energizing the EGR control 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 PCM 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.

. By grounding the diagnostic terminal, the EGR solenoid should be energized and allow vacuum to be applied to the EGR valve and the vacuum should hold.

. 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.

. This test will determine if the electrical control part of the system is at fault or if the connector or solenoid is at fault.

. This system has a negative backpressure EGR valve which should hold vacuum with engine "OFF".

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

Diagnostic Aids:
Before replacing PCM, use ohmmeter and check resistance of each PCM controlled relay and solenoid coil. Refer to "PCM Wiring Diagram" for coil terminal identification of solenoids and relays to be checked. Replace any relay or solenoid if the coil resistance measures less than 20 ohms.