Exhaust Gas Recirculation (EGR) System Check

Chart C-7:

EGR Wiring Diagram:

EGR SYSTEM CHECK

CIRCUIT DESCRIPTION:

The integrated electronic EGR valve functions similar to a standard EGR (ported vacuum) valve with a remote vacuum regulator. The internal solenoid is normally open (vacuum is vented to atmosphere when the ECM is not signalling the EGR). The EGR valve has a sealed cap. The solenoid valve opens and closes the vacuum signal, which varies the amount of vacuum vented to atmosphere and to the diaphragm. The electronic EGR valve contains a voltage regulator which converts the ECM signal to vary the amount of exhaust gas flow and current to the solenoid. The ECM controls exhaust gas flow with a pulse width modulated signal based on airflow, throttle position, and engine rpm.
This system also contains a pintle position sensor, similar to a TPS. As exhaust gas flow increases, the sensor output increases.




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

1. Whenever the solenoid is not powered, the solenoid valve should be open (the EGR diaphragm should NOT be moving). If the filter is plugged, the vacuum applied with a hand held pump will cause the diaphragm to move due to the vacuum not being allowed to vent.
2. This test determines if the EGR filter is plugged or if the EGR is at fault. Be carefull removing the filter to avoid damage to the EGR assembly (see MAINTENANCE PROCEDURES).
3. If the valve moves in this test, it is probably due to circuit 435 being shorted to ground.
4. Grounding the diagnostic terminal should energize the solenoid to close the vent, and allow the vacuum to move the EGR valve diaphragm.
5. The EGR assembly is designed to have some leakage. Seven inches (Hg) of vacuum is all that is necessary on the assembly, but if a large leak exists, less than 3" Hg, the EGR assembly is leaking and needs to be replaced.

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





DIAGNOSTIC AIDS:

The EGR position voltage can be used to determine if the pintle is moving. When zero duty cycle (no duty cycle) is commanded from the ECM, the position sensor should read between .5 to 1.5 volts. The voltage should increase as duty cycle increases.




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.