Diagnostic Test Procedures

Fig. 17 Entering Diagnostic Service Mode:

Fig. 18 Entering Diagnostic Service Mode:

Fig. 19 Entering Diagnostic Service Mode:

After trouble codes have been displayed, the diagnostic service mode can be used to test the speed control system by referring to Figs. 17 through 19 and performing the following:
1. On models less CRT, proceed as follows:
a. Following the display of trouble codes, the first available system level will be displayed, which is the ECM. On 1989 models, depress Lo fan button (secondary display) to enter into BCM system. On 1990 models, depress fan down button to enter BCM system.
b. On 1989 models, depress Hi fan button (secondary display). On 1990 models, depress fan up button. This will display the first available test type.
c. On 1989 models, press Lo fan button (secondary display), on 1990 models, depress fan down button to change the display to ``Inputs,'' the test level required for speed control system testing.
d. On 1989 models, depress Hi fan button (secondary display) and on 1990 models, depress fan up button. This will display the first test type. At this point, press Hi button until the correct test type appears as listed below under the applicable model and year.
2. On models with CRT, proceed as follows:
a. Following the display of trouble codes, the first available system level will be displayed, which is the ECM. Depress No button on secondary display to enter into BCM system.
b. Depress Yes button on secondary display. This will display the first available test type.
c. Press No button on secondary display to change the display to ``Inputs,'' the test level required for speed control system testing.
d. Depress Yes button on secondary display. This will display the first test type. At this point, press Yes button until the correct test type appears as listed below under the applicable model and year.
When performing the following tests, refer to applicable wiring diagram and connector pin locations, SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC DIAGRAMS.
1. Enter BCM diagnostics, turn ignition switch to Run position, select BCM input BI75 and operate cruise switch.
2. If BCM BI75 display reads Lo with cruise switch on, proceed as follows:
a. Check fuse No. 18.
b. Disconnect multi-function lever connector and, using test lamp, check for voltage at terminal A (pink/white wire). If there is no voltage check pink/white wire (circuit 350) for open.
c. Connect fused jumper between terminals A (pink/white wire) and B (gray wire) of multi-function lever. If display reads Hi, replace multi-function lever.
d. If display reads Lo, reconnect multi-function lever connector and, with cruise switch on, backprobe BCM terminal 1C11 (gray/white wire) with a test lamp to ground.
e. If lamp does not illuminate, on 1989 models, check gray/white wire (circuit 397) for open. On 1990 models, check gray wire (circuit 397) for open.
f. If lamp illuminates, check contact terminal 1C11 and, if terminal is satisfactory, replace BCM.
3. If BI75 display reads Hi with cruise switch off, proceed as follows:
a. Disconnect multi-function lever. If display reads Lo, replace multi-function lever.
b. If display reads Hi, check gray wire (circuit 397) or, on 1990 models, check brown wire (circuit 86) for short to battery and, if wire is satisfactory, replace BCM.
4. If BCM BI75 displays Lo with cruise switch off and Hi with cruise switch on, turn ignition switch to Run position, place cruise control switch in On position, select BCM input BI71 and operate brake pedal.
5. If BI71 displays Lo with cruise switch in On position and brake pedal released, proceed as follows:
a. Connect test lamp between terminal A (gray/white wire) of connector C2 of brake switch and ground. If lamp illuminates proceed to step c.
b. If lamp does not illuminate, backprobe terminal B (gray wire) of multi-function lever. If lamp illuminates, check gray and gray/white wires (circuit 397) for an open. If lamp does not illuminate, repeat test.
c. If lamp illuminated in step a, on 1989 models, connect jumper wire between terminals A (gray/white wire) and B (brown wire) of brake switch. On 1990 models, connect jumper wire between terminals A (gray wire) and B (brown wire) of brake switch. On all models, if display reads Hi, check brake switch adjustment and, if adjustment is correct, replace brake switch.
d. If display reads Lo, backprobe BCM terminal 1C1 (brown wire) with a test lamp to ground. If lamp does not illuminate, check brown wire (circuit 86) for an open. If lamp illuminates, check BCM terminal contact 1C1 and, if terminal is satisfactory, replace BCM.
6. If BI71 displays Hi with cruise switch in On position and brake pedal depressed, disconnect brake switch.
7. If display reads Lo, adjust or replace brake switch.
8. If display reads Hi, check brown wire (circuit 86) for short to battery and, if short is not found, replace BCM.
9. If BCM BI71 display reads Lo with cruise switch on and brake pedal depressed, and reads Hi with cruise switch on and brake pedal released, turn ignition switch to Run position, place cruise switch in On position, select BCM input BI76 and operate set switch.
10. If B176 display reads Lo with cruise switch on and set switch depressed, proceed as follows:
a. Check fuse No. 18
b. Disconnect multi-function lever connector and, using test lamp, check for voltage at terminal A (pink/white wire). If there is no voltage, check pink/white wire (circuit 350).
c. Connect jumper wire between terminals A (pink/white wire) and D (dark blue wire) of multi-function lever. If display reads Hi, replace multi-function lever.
d. If display reads Lo, reconnect multi-function lever connector and, with cruise switch on and set switch depressed, connect test lamp to ground and backprobe BCM connector 1C4 (dark blue wire). If lamp does not illuminate, repair dark blue wire (circuit 84). If lamp illuminates, check BCM terminal contact 1C4 and, if contact is satisfactory, replace BCM.
11. If B176 display reads Hi with cruise switch on and set switch released, disconnect multi-function switch connector.
12. If display reads Lo, replace multi-function lever.
13. If display reads Hi, check dark blue wire (circuit 84) for short to battery and, if short is not found, replace BCM.
14. If BCM BI76 display reads Lo with cruise switch on and set switch released and reads Hi with cruise switch on and set switch depressed, turn ignition switch to Run position, select BCM input BI77 and operate cruise switch.
15. If BI77 display reads Lo with cruise switch on and resume switch depressed, proceed as follows:
a. Check fuse No. 18.
b. Disconnect multi-function lever connector and, using test lamp, check for voltage at terminal A (pink/white wire). If there is no voltage check pink/white wire (circuit 350).
c. Connect jumper wire between terminals A (pink/white wire) and C (gray/black wire) of multi-function lever. If display reads Hi, replace multi-function lever.
d. If display reads Lo, reconnect multi-function lever connector and, with cruise switch on and resume switch depressed, connect test lamp to ground and backprobe BCM connector 1C14 (gray/black wire). If lamp does not illuminate, repair gray/black wire (circuit 87). If lamp illuminates, replace BCM.
16. On 1989 models, if B177 display reads Hi with cruise switch on and resume switch released, disconnect multi-function lever connector.
17. If display reads Lo, replace multi-function lever.
18. If display reads Hi, check gray/black wire (circuit 87) for short to battery and, if wire is satisfactory, replace BCM.

Fig. 12 Code B667:

19. On 1990 models, if display reads Hi, with cruise switch on, refer to test B667, Fig. 12, for procedure.
20. On all models, if BCM BI77 display reads Lo with cruise switch off, or with cruise switch on and resume switch released, and reads Hi with cruise switch on and resume switch depressed, enter BCM output BO01 and place cruise switch in On position. BCM BO01 display and vent valve solenoid should both cycle. (a clicking should be heard as relay cycles).

Fig. 14 Code B672:

21. If vent valve does not cycle (no clicking is heard) refer to code B672, Fig. 14.
22. If vent valve cycles (clicking is heard) enter BCM output BO02 and place cruise switch in On position. BCM BO02 and vacuum valve solenoid should both cycle. (Clicking noise should be heard as relay cycles).

Fig. 15 Code B673:

23. If vacuum valve solenoid does not cycle (clicking noise is not heard) refer to code B673, Fig. 15.
24. If vacuum valve solenoid cycles (clicking noise is heard) start engine and run for 2 minutes, turn engine off, turn ignition switch to Run position and select BCM override BS05.
25. With override cycling from 0 to 99 and back to 0, cruise control servo should pull fully in and then release. If so, replace BCM.
26. If cruise control servo does not pull fully in and then release, check vacuum source and hoses for leaks, kinks and/or restrictions and check cruise control servo for mechanical binding.
27. If vacuum and mechanism are satisfactory, replace cruise control servo.