Exhaust Gas Recirculation (EGR) System Check

Chart C-7:

EGR Wiring Diagram:

EGR SYSTEM CHECK

CIRCUIT DESCRIPTION:

The digital EGR valve is designed to accurately supply exhaust gas to the engine without the use of manifold vacuum. The valve controls exhaust gas flow from the exhaust system to the intake manifold through three orifices, to produce seven combinations. When the solenoid is energized, the armature, combined with an attached shaft and swivel pintle, is raised and the orifice is opened.
The flow accuracy is dependent on the orifice size only, which results in improved EGR control.




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

1. EGR #1 should result in a small RPM change.
EGR #2 should result in a larger RPM change.
EGR #3 should result in the largest RPM change.
2. This checks for open circuits from the EGR to the ECM.

NOTE:

In the preceeding test the scan tool is grounding each EGR solenoid individually through a quad driver circuit in the ECM. Grounding the solenoids will open the passage and cause a drop in engine RPM.

NOTE:

If the digital EGR valve shows signs of excessive heat distortion, check the exhaust system for blockage (possibly a plugged converter) using the procedure in TESTING PROCEDURES, for CATALYTIC CONVERTER. If the exhaust system is restricted, repair the cause.




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.