Exhaust Gas Recirculation: Testing and Inspection

Chart C-7:

EGR Circuit:

CIRCUIT DESCRIPTION:

The EGR valve is controlled by a normally open, Pulse Width Modulated (PWM) solenoid. The ECM turns 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, CTS, 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 a 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 but 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. Use a "Scan" tool to check the Park/neutral switch. Chart C-1 Park/Neutral Switch Diagnosis