System Test

Chart C-7:

EGR Wiring Diagram:

EGR SYSTEM CHECK

CIRCUIT DESCRIPTION:

The EGR valve is controlled by a normally open, Pulse Width Modulated (PWM) solenoid. The ECM powers the solenoid off, to allow vacuum to flow to the EGR. The ECM turns the solenoid on to prohibit EGR operation.
The duty cycle is calculated by the ECM based upon information from the coolant temperature, MAT, TPS, and MAF sensors. The engine speed and Park/Neutral switch also affect EGR. There should be NO EGR flow in Park/Neutral, below TPS Calibrated value, or at wide open throttle.
With the ignition on and engine not running, the EGR solenoid is de-energized. The solenoid should be energized if the diagnostic terminal is grounded with the ignition on and engine off.



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

1. This tests the solenoid value to determine if it is capable of closing off the vacuum from the EGR valve. The vacuum can bleed off slowly (this should not be considered as a fault).
2. As soon as backpressure is present at the EGR valve, the bleed portion, in the valve, should open and allow the valve to move to its heated position.
3. The EGR will be inoperative if the Park/Neutral switch is mis-adjusted, or faulty. Use a computer diagnostic tool to check the Park/neutral switch.

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





INCORRECT EGR OPERATION:

1. If too much EGR is flowing at idle, cruise, or cold operation,
any of the following conditions could exist:
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.