Exhaust Gas Recirculation: Testing and Inspection

Chart C-7 Wiring Diagram:

Chart C-7 - EGR System Check:

CIRCUIT DESCRIPTION
The EGR valve is controlled by a normally closed solenoid (allows vacuum to pass when energized). The ECM signals the solenoid to control the amount of air bleed. As more air is allowed to bleed, less vacuum can be applied to the EGR valve, resulting in less EGR. The ECM diagnoses the system using an internal EGR test procedure.
The ECM control, of the EGR, is based on the following inputs:
- Engine coolant temperature - above 25° C
- TPS - "OFF" idle
- MAP

If Code 24 is stored, use that chart first.

Code 32 will detect a faulty solenoid, vacuum supply, EGR valve or plugged passage. This chart checks for plugged EGR passages, a sticking EGR valve, or a stuck open or inoperative solenoid.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. With the ignition "ON," engine stopped, the solenoid should not be energized and vacuum should not pass to the EGR valve.
2. Grounding the diagnostic terminal will energize the solenoid and allow vacuum to pass to valve.
3. Checks for plugged EGR passages. If passages are plugged, the engine may have severe detonation on acceleration.
4. The EGR solenoid will not be energized in PARK or NEUTRAL. This test will determine if the switch input is being received by the ECM.