Symptom Related Diagnostic Procedures

System tester J-34185 can be used to diagnose system malfunctions. The tester replaces the electronic cruise controller (module) in the system and is used to isolate defective components. If tester is not available, use following procedures to diagnose malfunctions.

PRELIMINARY CHECK
Perform these checks as the first step in diagnosing any cruise control complaint.
1. Road test vehicle for system operation and verify complaint.
2. Inspect vacuum hoses and fittings. Repair all loose connections, damaged fittings or hoses, and kinked, plugged or improperly routed hoses.
3. Inspect wiring harness, connectors and grounds. Repair loose or improper connections and damaged wiring or connectors.
4. Inspect servo and throttle linkage for binding or sticking, and repair as needed. Ensure that linkages are properly adjusted.
5. Recheck system operation.

VEHICLE SURGES IN CRUISE MODE
1. Perform preliminary checks.
2. Test servo as outlined in ``Component Testing.''
3. Perform electrical and vacuum system tests. If no system malfunction is noted, replace module and recheck system operation.

CRUISE SPEED ABOVE OR BELOW SET SPEED
1. Perform preliminary checks.
2. Perform electrical and vacuum system checks. If no system malfunction is noted, replace module and recheck system operation.

EXCESSIVE LOSS OF SPEED ON INCLINE
1. Check vacuum system for leaks and repair as needed.
2. Test check valve, if equipped, and replace as needed.

TAP-UP OR TAP-DOWN INOPERATIVE
If all other system functions operate correctly, replace cruise controller (module).

Fig. 3 Cruise control system diagnostic chart:

CRUISE CONTROL INOPERATIVE
Refer to Fig. 3 to diagnose an inoperative cruise control system.