Powertrain Controls - ECM/PCM

CIRCUIT DESCRIPTION
The ECM operates a vacuum solenoid to control the Exhaust Gas Recirculation (EGR) valve. This solenoid is normally closed. By providing a ground path, the ECM energizes the solenoid, allowing vacuum to reach the EGR valve.

Under certain conditions, when the EGR valve is normally open, the ECM tests the EGR function by deenergizing the EGR control solenoid, blocking vacuum to the EGR valve diaphragm. Without EGR, the system will sense a lean condition and will increase the fuel integrator rate in response. The ECM monitors the amount of fuel delivery increase. If the increase is below a specified value, the ECM will interpret that the test was failed. The failure indicates that closing the EGR valve when it would normally be open does not make a significant change, indicating a problem in the EGR system.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
The diagnostic chart covers checks for the entire EGR system. If no trouble is found but Code 32 was set, an intermittent electrical condition or a sticky EGR valve is at fault.

DIAGNOSTIC AIDS
The vacuum switch in the EGR solenoid assembly is not used.

An EGR valve stuck open will cause a rough idle.

A plugged EGR solenoid vent filter could cause the EGR valve to remain open or to close slowly.

An inoperative check valve in the ported vacuum line will result in faulty EGR system operation.