OBD Testing - Switch Tests

To perform the switch test series, the engine must be running and the code .7.0 must be displayed on the data center panel. To begin the test sequence, depress and release the brake pedal, and the test will begin as soon as the display changes from code .7.0 to code E.7.1. If the code does not change, check brake switch feed to the ECM and check for defective ECM refer to, SYSTEM DIAGNOSTIC CHARTS and SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC DIAGRAMS/ELECTRICAL CONNECTORS.
The ECM will display a code for each switch, in sequence, and if the switch does not operate properly, the ECM will store the code as a trouble code. In addition, the appropriate switch must be cycled within 10 seconds after its code is displayed or the ECM will store a trouble code associated with that switch. Perform switch tests as follows:
1. When performing the following tests, refer to wiring diagrams and connector points under Cruise Control/Diagrams/Electrical.
2. With code E.7.1 displayed, depress and release brake pedal again to test cruise control brake switch circuit.
3. With code E.7.2 displayed, depress accelerator pedal from idle position to open throttle, then slowly release pedal. As throttle is moved the ECM tests throttle switch for proper operation.
4. On 1990 models, with code 7.3 displayed, operate the transmission in 3rd gear to test 3rd gear pressure switch.
5. On 1991 models, with code E.7.3 displayed, move transmission selector into reverse, then neutral to test operation of park/neutral switch.
6. On 1989 models, with code E.7.4 displayed, move transmission selector into reverse, then neutral to test operation of park/neutral switch.
7. On all models, with code E.7.5 displayed, turn cruise control instrument panel switch from off to on, then back to off to test operation of switch. Refer to SYSTEM DIAGNOSTIC CHARTS for further testing procedure. For intermittent codes proceed as follows:
a. The amber cruise-on indicator can be used to monitor the cruise dash switch status. Turn dash switch on and wiggle wiring and connectors. If switch or circuit from the fuse to switch are open, the amber light will blink out.
b. If cruise fuse blows intermittently, turn switch on, then wiggle wiring, connectors and cruise steering column switch. If circuit becomes grounded, fuse will blow.
8. With code E.7.6 displayed and with instrument panel cruise control switch on, depress and release set/coast button to test set/coast button operation. Refer to SYSTEM DIAGNOSTIC CHARTS for further testing procedure. For intermittent codes proceed as follows:
a. Turn cruise dash switch to on and backprobe ECM B4 with a voltmeter to ground. B4 should show 12 volts with set/coast depressed and 0 volts with switch released. While observing meter, cycle switch and wiggle wiring and connectors.
9. With code E.7.7 displayed and with instrument panel cruise control switch on, depress and release resume/acceleration switch to test operation of switch. Refer to SYSTEM DIAGNOSTIC CHARTS for further testing procedure. For intermittent codes proceed as follows:
a. Turn cruise dash switch to on and backprobe ECM B6 with a voltmeter to ground. B6 should show 12 volts with resume/acceleration switch depressed and 0 volts with switch released. While observing meter, cycle switch and wiggle wiring and connectors.
10. With code E.7.8 displayed, turn steering wheel to full lock in both directions, then return wheel to straight ahead position to test power steering pressure switch operation.
11. When the switch tests are completed, the ECM will go back and display codes for switches which did not test properly.
12. Check circuit between each switch that failed and the ECM, test switches individually, repair as needed, then clear trouble codes and retest system.
13. If malfunction persists, check Fuel Injection.