Chart C-7 EGR System Check - Port Fuel Injection

Chart C-7:

Wiring Diagram:

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, IAT, TPS, and MAP sensors. The engine rpm and Park/Neutral switch also affect EGR. There should be NO EGR flow in Park/Neutral, TPS below Calibrated value, or at wide open throttle.
With the ignition "ON" and engine "OFF", 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 seated position.

3. The EGR will be inoperative if the Park/Neutral switch is mis-adjusted, or faulty. The EGR is disabled when in park or neutral. Use a computer diagnostic tool to check the Park/neutral switch. Refer to CHART C-1A.

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


DIAGNOSTIC AIDS:

Suction from shop exhaust hoses can alter backpressure and may affect the function check of the EGR valve.
Thoroughly check that the EGR vacuum harness is not plugged or restricted. If the vacuum harness is pushed on the solenoid too far, it may plug the end of the vacuum lines and cause the EGR to be inoperative. Make sure vacuum lines are at the right locations of the EGR solenoid.