System Diagnosis - EGR

Fig. 36 Emission control system wiring circuit:

1. Run engine until normal operating temperature is reached. Increase engine speed from idle to approximately 2000 RPM and observe EGR valve diaphragm.
2. If EGR valve diaphragm moves as engine speed is increased, proceed as follows:
a. With engine running, push up on underside of EGR valve and note change in engine speed.
b. If engine speed decreases, the EGR system is functioning properly. If there is no change in engine speed, clean EGR passages or replace valve as needed.
3. If EGR valve diaphragm does not move as engine speed is increased, proceed as follows:
a. Turn ignition on and enter Code .9.6. Disconnect EGR solenoid electrical connector and connect a test lamp between harness connector pins.
b. If test lamp does not light, proceed to step 3c. If test lamp lights steady, proceed to step 3d. If test lamp flashes in three second intervals, proceed to step 3e.
c. Check condition of 10 amp IGN fuse. If fuse is blown, repair short to ground in circuit 639 and replace fuse. If fuse is satisfactory, check circuits 435 and 639, Fig. 36, for an open. If circuits are satisfactory, measure resistance across EGR solenoid in both directions. If both readings are less than 20 ohms, replace solenoid and ECM. If either reading is greater than 20 ohms, fault is in ECM or ECM connector. Repair or replace as necessary.
d. Check circuit 435 for a short to ground. If circuit is satisfactory, fault is in ECM or ECM connector. Repair or replace as necessary.
e. Reconnect EGR solenoid electrical connector and disconnect EGR valve vacuum supply line. Connect suitable vacuum gauge to vacuum supply line and note change in vacuum when engine speed is increased from idle to approximately 2000 RPM. If vacuum never falls below 3 inches Hg, replace EGR solenoid. If vacuum never rises above 7 inches Hg, check vacuum hoses for leaks or restrictions. If vacuum hoses are satisfactory, replace EGR solenoid. If vacuum rises above 7 and falls below 3 inches Hg, replace EGR valve.