Exhaust Gas Recirculation: Testing and Inspection

Three EGR system problems will cause the ECM to illuminate the "CHECK ENGINE" light:

1. Excessive temperature will cause the ECM to shut down the system and store a fault code.
2. EGR system not operating in programmed speed/load range will store a fault code.
3. EGR system operating at too low temperature will cause the ECM to shut down the system and store a fault code.

EGR system fault codes are 37 and 39. Code 37 sets if ECM output to the vacuum control solenoid is incorrect. Code 39 sets if the ECM detects EGR temperature sensor readings out of programmed ranges. Incorrect temperatures indicate system malfunctions.

ROUGH IDLE CHECK

1. Warm engine to operating temperature. Set parking brake, block wheels and place gear selector in "D."
2. Remove vacuum hose from EGR valve.
3. Raise engine speed to 1100 rpm.
4. Check for vacuum at open hose end.
5. If vacuum is detected below 1100 rpm, hoses at vacuum solenoid may be connected backward. Reverse connections and recheck.

EGR VALVE DIAPHRAGM CHECK

NOTE: A split or porous diaphragm is the most common cause of EGR valve failure.

1. Remove vacuum hose from EGR valve.
2. From beneath valve, push diaphragm up and hold in position. Block vacuum hose connection on top of valve. Release diaphragm and it should remain in position. If not, diaphragm is leaking and EGR valve assembly should be replaced.