Exhaust Gas Recirculation: Testing and Inspection

Chart C-7A - EGR Check:

Wiring Diagram for EGR Check:

CHART C-7A EXHAUST GAS RECIRCULATION (EGR) CHECK


Circuit Description:

The Exhaust Gas Recirculation (EGR) valve is controlled by a normally open pulse width modulated (PWM) solenoid. The ECM turns the solenoid "OFF" to allow vacuum to pass to the EGR and turns the solenoid "ON" to prohibit EGR operation. When EGR is commanded, the solenoid is turned "ON" and "OFF" many times a second (duty cycle).

The duty cycle is calculated by the ECM based on information from the coolant, MAT, TPS, and MAF sensors. Also, engine rpm's and the P/N switch input affect EGR. There should be no EGR when in park or neutral, TPS below a calibrated value or TPS indicating WOT.

With the ignition "ON" and engine stopped, the EGR solenoid is de-energized. The solenoid should be energized if the diagnostic terminal is grounded with the ignition "ON" and engine not running.





Test Description: Numbers below refer to circled numbers on the diagnostic chart.


1. This will test the solenoid value to determine if it is capable of closing off the manifold vacuum from the EGR valve. The vacuum may bleed off slowly but this should not be considered faulty.






2. As soon as back pressure is available at the EGR valve, the bleed portion in the valve should open and cause the valve to go to its seated position.

3. The EGR will be inoperative if the P/N switch is misadjusted or faulty. Use "Scan" tool and check P/N switch. Refer to CHART C-1A in Computerized Engine controls.