System Diagnosis - Models With D.E.F.I.
Fig. 2 Cruise control diagnosis chart. Models w/D.E.F.I.:
The operation of the cruise control system is integrally linked with the Digital Electronic Fuel injection system (DEFI). The DEFI system control module includes a self-diagnostic function, and in order to diagnose malfunctions within the cruise control system this self-diagnosis system must be accessed. Refer to Fig. 2 and the following procedures in order to access trouble codes pertaining to the cruise control system and diagnose system malfunctions.
Codes other than those described below may be stored in the control module memory and displayed when the system is accessed to diagnose cruise control malfunctions. It may be necessary to identify and diagnose the failures caused by these additional codes in order to ensure proper system operation. For complete diagnosis of the DEFI system, refer to COMPUTERIZED ENGINE CONTROLS.
SELF-DIAGNOSIS SYSTEM
The DEFI control module is capable of monitoring microprocessor controlled sub-systems. By comparing the actual system operating conditions to standard values stored in the control module memory, the module can detect certain system malfunctions. When the module senses a malfunction a two digit failure code is stored in the memory, and these trouble codes can be displayed to aid in system diagnosis. Use the following procedures to operate the self-diagnosis system.
Entering Self-Diagnostic Mode
1. Turn ignition switch on.
2. Simultaneously depress the OFF and WARMER buttons on the climate control panel and hold buttons until all display panel segments are illuminated which indicates the beginning of the diagnostic readout. The purpose of illuminating the two display panels is to ensure that all segments are working. If any segments are are inoperative, the affected display panel must be replaced.
3. After the display segment check is completed, any stored trouble code will be displayed on the data center. These two-digit codes will be displayed with a prefix of either E or F to designate which computer sensed the malfunction. If a trouble code is displayed, or if the self-diagnostics system cannot be accessed, a defect has been sensed in the vehicle's electronic control system. To diagnose these malfunctions, refer to COMPUTERIZED ENGINE CONTROLS.
4. After all codes are displayed or if no trouble codes are stored, the code .7.0 will appear on the display.
Code .7.0
Code .7.0 is a decision point. When this code is displayed, the diagnostic feature relevant to the current malfunction can be selected. The two diagnostic modes relevant to cruise control diagnosis, ECM switch tests and ECM output cycling, are detailed below.
Clearing Trouble Codes
The trouble codes stored in the system memory can be cleared to aid in diagnosing intermittent conditions. To clear codes, proceed as follows:
1. Enter diagnostic mode as outlined.
2. To clear engine control module (ECM) codes, simultaneously depress the OFF and HI buttons on the climate control panel and hold the buttons until the code E.0.0 is displayed.
3. To clear body control module (BCM) codes, simultaneously depress the OFF and LO buttons on the climate control panel and hold until the code F.0.0 is displayed.
4. After E.0.0 and F.0.0 are displayed, the code .7.0 will be displayed. With this code displayed, turn off ignition and leave ignition off for at least 10 seconds before re-entering the diagnostic mode.
Exiting Self-Diagnostic Mode
To exit the self-diagnostic mode, depress the AUTO button on the climate control panel or turn of ignition for at least 10 seconds.
ECM SWITCH TEST SERIES
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.
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. With code E.7.1 displayed, depress and release brake pedal again to test cruise control brake switch circuit.
2. 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.
3. With code E.7.4 displayed, move transmission selector into reverse, then neutral to test operation of park/neutral switch.
4. With code E.7.5 displayed, move cruise control instrument panel switch from off to on, then back to off to test operation of switch.
5. With code E.7.6 displayed and with instrument panel cruise control switch on, then depress and release set/coast button to test set/coast button operation.
6. With code E.7.7 displayed and with instrument panel cruise control switch on, depress and release resume/acceleration switch to test operation of this switch.
7. 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.
8. When the switch tests are completed, the ECM will go back and display codes for switches which did not test properly.
9. Check circuit between each switch that failed and the ECM, test switches individually, repair as needed, then clear trouble codes and retest system.
10. If malfunction persists, refer to COMPUTERIZED ENGINE CONTROLS.
ECM OUTPUT CYCLING
ECM output cycling can be tested after code E.9.5 is displayed on the data center. Code E.9.5 can be reached by depressing the HI button on the climate control panel when code .7.0 is displayed. The ECM output cycling mode, code E.9.6, will then cycle ECM outputs on and off. To enter output cycling mode, proceed as follows:
1. With engine running, turn ignition off, then within 2 seconds turn ignition back on.
2. Enter self-diagnostic mode and obtain code E.9.5 as outlined above.
3. Depress and release accelerator pedal (open and close throttle switch), and the display code E.9.6 should appear. If not, check throttle switch signal as outlined.
4. Turn cruise control switch on and observe system operation. The cruise power solenoid should cycle on and off rapidly, and the cruise vacuum valve should cycle on and off every 3 seconds.
5. The output cycling mode will stop automatically after 2 minutes and the display code will return to E.9.5
6. If the system fails to operate as outlined, check wiring between effected component and ECM, test components individually, repair as needed, then clear trouble codes and repeat test. If malfunction persists, refer to COMPUTERIZED ENGINE CONTROLS.