Exhaust Gas Recirculation: Testing and Inspection

Chart C-7:

EGR Circuit Wiring Diagram:

EGR SYSTEM CHECK

CIRCUIT DESCRIPTION:

The ECM operates the vacuum solenoid to control the EGR valve. The solenoid is normally closed. The ECM provides a ground path to energize the solenoid. This allows vacuum to flow to the EGR valve.
When the EGR is open, the ECM tests the EGR function by powering off the EGR solenoid, which blocks vacuum to the EGR valve diaphragm. Without the EGR, the system will sense a lean condition and increase the fuel integrator rate response. If an increase is below a specified value, the ECM will interpret that the test has failed. The failure indicates that closing the EGR valve, when it is normally open, does not make a significant change, and this indicates a problem in the EGR system.


TEST DESCRIPTION:

The diagnostic chart covers checks for the entire EGR system. If no trouble is found but a code 32 is present, an intermittent electrical condition or a sticky EGR valve is at fault.

NOTE: Once the test sequence is completed, clear codes and verify NO "SERVICE ENGINE SOON" light exists.



DIAGNOSTIC AIDS:

1. The vacuum switch in the EGR solenoid assembly is not used.
2. An EGR valve stuck open will cause a rough idle.
3. A plugged EGR solenoid vent filter could cause the EGR valve to remain open or close slowly.
4. An inoperative check valve, in the ported vacuum line, will cause a fault in the EGR system operation.




INCORRECT EGR OPERATION:

1. If too much EGR is flowing at idle, cruise, or cold operation,
any of the following conditions could exists:
a. The engine dies after cold start.
b. The engine stalls on deceleration.
c. The vehicle surges during cruise mode.
d. Rough idle.

2. If too little or no exhaust gases flow, the combustion chamber temperature may increase under acceleration or heavy load conditions. These conditions could cause:
a. Detonation (Spark Knock).
b. The engine to overheat.
c. The emissions test to fail.