Entering Diagnostic Service Mode

Fig. 16 Entering Diagnostic Service Mode:

Fig. 18 Entering Diagnostic Service Mode:

On 1989 models, to enter the diagnostic service mode, turn ignition on, then depress Off and Warm pads on the CRT's Climate Control page simultaneously. Hold until a double beep is heard or a page entitled Service Mode is displayed.

On 1990 models, to enter the diagnostic service mode, turn ignition on, then depress Off and Temp Up pads on the Electronic Climate Control Panel (ECCP) simultaneously. Hold until all display segments have been lite.

Operating vehicle in diagnostic service mode for extended time periods without the engine running will cause the battery to run down and possibly relate false diagnostic information. To ensure proper operation do not operate in diagnostic service mode for longer than 1/2 hour.


After trouble codes have been displayed, the diagnostic service mode can be used to test the speed control system by referring to Figs. 16 and 18 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 diagrams and connector pin locations.
1. Turn ignition switch to Run position, enter BCM diagnostics, select BCM input test BI75 and operate cruise switch.

2. If BI75 displays Hi with cruise switch off, proceed as follows:
a. Disconnect multi-function lever harness electrical connector.
b. If display reads Lo, replace multi-function lever.
c. If display reads Hi, reconnect multi-function lever assembly, and backprobe BCM terminal 1C11 (gray/white wire) to ground with voltmeter.
d. If battery voltage is present, on 1989 models, check gray/white wire (circuit 397) for short to battery. On 1990 models, check gray wire (circuit 397) or brown wire (circuit 86) for short to battery.
e. On all models, if battery voltage is not available, on 1989 models, check BCM terminal 1C11 (gray/white wire) for a good and clean connection and, on 1990 models, check BCM terminal 1C11 (gray wire) for a good and clean connection then, on all models, if terminal is satisfactory, replace BCM.

3. If BI75 displays Lo with cruise switch on, proceed as follows:
a. Check fuse No. 8.
b. If fuse is not blown, proceed to step h.
c. If fuse is blown, place cruise switch in Off position and replace fuse No. 8.
d. If fuse blows, check pink/white wire (circuit 350) for short to ground.
e. If fuse does not blow, hold brake pedal in depressed position and place cruise switch in On position.
f. If fuse blows, check gray/white wire (circuit 397) for short to ground.
g. If fuse does not blow, proceed to step 4.
h. If fuse did not blow in step b, disconnect multi-function lever assembly and connect a test lamp between terminal BC11 (pink/white wire) and ground.
i. If lamp does not illuminate, check pink/white wire (circuit 350) for an open.
j. If lamp illuminates, on 1989 models, connect fused jumper between terminals BC11 (pink/white wire) and BC10 (gray/white wire) of multi-function lever assembly. On 1990 models, connect fused jumper between terminals A (pink/white wire) and B (gray wire) of multi-function lever assembly.
k. On all models, if display reads Hi, replace multi-function lever assembly.
l. If display reads Lo, reconnect multi-function lever assembly, place cruise switch in On position and backprobe BCM terminal 1C11 (gray/white wire) to ground with a voltmeter.
m. If battery voltage is not available, on 1989 models, check gray/white wire (circuit 397) for an open. On 1990 models, check gray wire (circuit 397) for an open.
n. On all models, if battery voltage is available, check BCM terminal 1C11 (gray/white wire) for good terminal contact and, if contact is good, replace BCM.

4. If BCM display reads Hi with cruise switch on and Lo with cruise switch off, place ignition switch in Run position, place cruise switch in On position, enter BCM diagnostics, select BCM input test BI71 and operate brake pedal.

5. If BI71 displays Hi with brake pedal depressed, proceed as follows:
a. Remove brake switch connector C2.
b. If display reads Lo, check brake switch adjustment and, if adjustment is satisfactory, replace brake switch.
c. If display reads Hi, disconnect BCM and connect voltmeter between BCM terminal 1C1 (brown wire) and ground.
d. If battery voltage is available, check brown wire (circuit 86) for short to battery.
e. If battery voltage is not available, check BCM terminal 1C1 (brown wire) for a good clean connection and, if connection is good, replace BCM.

6. On 1989 models, if BI71 displays Lo with brake pedal released, proceed as follows:
a. Check fuse No. 8.
b. If fuse is blown, disconnect BCM and replace fuse No. 8.
c. If fuse does not blow, check BCM terminal 1C1 (brown wire) for a good and clean connection and, if connection is good, replace BCM.
d. If fuse blows disconnect brake switch connector C2, replace fuse No. 8 and connect test lamp between terminals A (gray/white wire) and B (brown wire).
e. If lamp does not illuminate, replace brake switch.
f. If lamp illuminates, check brown wire (circuit 86) for a short to ground.
g. If fuse is not blown in step a, remove brake switch connector C2 and connect test lamp between terminal A (gray/white wire) and ground.
h. If lamp does not illuminate, check gray/white wire (circuit 397) between splice S233 and brake switch for open.
i. If lamp illuminates, connect terminals A (gray/white wire) and B (brown wire) of brake switch connector with a fused jumper.
j. If display reads Hi, replace brake switch.
k. If display reads Lo, reconnect brake switch connector and backprobe BCM terminal 1C1 (brown wire) to ground with a voltmeter.
l. If battery voltage is available, check brown wire (circuit 86) for an open.
m. If battery voltage is available, check BCM terminal 1C1 (brown wire) for good terminal contact and, if contact is good, replace BCM.

7. On 1990 models, if B171 displays Lo with cruise switch on and brake released, proceed as follows:
a. Connect a fused jumper wire between terminal A (gray wire) and terminal B (brown wire) of brake switch connector.
b. If display reads Hi, ensure proper brake switch adjustment. I adjustment is good, replace brake switch.
c. If display reads Lo, with jumper wire still connected, back probe BCM terminal 1C1.
d. If test lamp does not light, check brown wire (circuit 86) for open.
e. If test lamp lights, check BCM terminal contact. If terminal contact is good, replace BCM.

8. On all models, if BCM display reads Lo with brake pedal depressed and Hi with brake pedal released, turn ignition switch to Run position, place cruise switch in On position, enter BCM diagnostics, select BCM input test BI76 and operate set/coast switch.

Fig. 12 Code B667:

9. If BI76 displays Hi with set/coast switch released refer to code B667, Fig. 12.

10. On 1989 Riviera, if BI76 displays Lo with set/coast switch depressed, proceed as follows. If cruise On indicator does not illuminate, repeat test.
a. Disconnect cruise switch assembly and connect test lamp between gray/white wire terminal connector and ground.
b. If lamp does not illuminate, check gray/white wire (circuit 397) between splice S233 and cruise switch assembly.
c. If lamp illuminates, connect test lamp between gray/white wire terminal and dark blue wire terminal of cruise switch assembly.
d. If display reads Hi, replace cruise switch assembly.
e. If display reads LO, reconnect cruise switch assembly and backprobe BCM terminal 1C4 (dark blue wire) to ground with a test lamp while depressing set/coast switch.
f. If lamp does not illuminate, check dark blue wire (circuit 84).
g. If lamp illuminates, check BCM terminal 1C4 (dark blue wire) for good terminal contact and, if contact is good, replace BCM.

11. On 1989 Reatta, if BI76 displays Lo with set/coast switch depressed, perform steps 4 through 6, then proceed as follows:
a. Disconnect C217 and connect test lamp between terminal W (brown wire) and terminal Z (dark blue wire).
b. If lamp does not illuminate, check brown wire (circuit 86) between splice S271 and connector C217.
c. If lamp illuminates, connect test lamp between terminal W (brown wire) and terminal Z (dark blue wire).
d. If display reads Hi, replace cruise switch assembly.
e. If display reads Lo, reconnect connector C217 and backprobe BCM terminal 1C4 (dark blue wire) with test lamp while depressing set/coast switch.
f. If lamp does not illuminate, check dark blue wire (circuit 84).
g. If lamp illuminates, check BCM terminal 1C4 (dark blue wire) for good terminal contact and, if contact is good, replace BCM.

12. On 1990 Reatta and Riviera, if B176 displays Lo with cruise switch on and set switch depressed, proceed as follows:
a. Connect fused jumper wire between terminal A (pink/white wire) and terminal D (dark blue wire) at multi-function lever connector.
b. If display reads Hi, replace multi-function lever if terminal contact is good.
c. If display reads Lo, reconnect multi-function lever connector, then with cruise switch on and set switch depressed, connect test lamp to ground and backprobe BCM terminal 1C4.
d. If test lamp does not light, check dark blue wire (circuit 84) for open.
e. If test lamp lights, check BCM terminal connector 1C4, if contact is good, replace BCM.

13. On all models, if BCM display reads HI with set/coast switch depressed and Lo with set/coast switch released, turn ignition switch to Run position, place cruise switch in On position, enter BCM diagnostics, select BCM input test BI77 and operate resume/accel switch.

14. If BI77 displays Hi with resume/accel switch released, refer to code B667, Fig. 12.

15. On 1989 Riviera, if BI77 displays Lo with resume/accel switch depressed, proceed as follows. If cruise On indicator does not illuminate, repeat test.
a. Disconnect cruise switch assembly and connect test lamp between gray/white wire terminal connector and ground.
b. If lamp does not illuminate, check gray/white wire (circuit 397) between splice S233 and cruise switch assembly.
c. If lamp illuminates, connect test lamp between gray/white and gray/black wire terminals of cruise switch assembly.
d. If display reads Hi, replace cruise switch assembly.
e. If display reads Lo, reconnect cruise switch assembly and backprobe BCM terminal 1C14 (gray/black wire) to ground with a test lamp while depressing resume/accel switch.
f. If lamp does not illuminate, check gray/black wire (circuit 87).
g. If lamp illuminates, check BCM terminal 1C14 (gray/black wire) for good terminal contact and, if contact is good, replace BCM.

16. On 1989 Reatta, if BI77 displays Lo with resume/accel switch depressed, proceed as follows. Before proceeding, perform steps 4 through 6.
a. Disconnect connector C217 and connect a test lamp between terminal W (brown wire) and ground.
b. If lamp does not illuminate, check brown wire (circuit 86) between splice S271 and connector C217.
c. If lamp illuminates, connect test lamp between terminals W (brown wire) and Y (gray/black wire).
d. If display reads Hi, replace cruise switch assembly.
e. If display reads Lo, reconnect connector C217 and backprobe BCM terminal 1C14 (gray/black wire) to ground while depressing resume/accel switch.
f. If lamp does not illuminate, check gray/black wire (circuit 87).
g. If lamp illuminates, check BCM terminal 1C14 (gray/black wire) for good terminal contact and, if contact is good, replace BCM.

17. On 1990 models, if B177 displays Lo with cruise switch on and resume switch depressed, proceed as follows:
a. Ensure steps 1 through 4 of this procedure are verified.
b. Connect fused jumper wire between multi-function lever connector terminals A and C.
c. If display reads Hi, replace multi-function lever.
d. If display reads Lo, reconnect multi-function lever, with cruise switch on and resume switch depressed, connect test lamp to ground and backprobe BCM connector 1C14.
e. If test lamp does not light, check gray/black wire (circuit 87) for open.
f. If test lamp lights, check BCM connector 1C14. If contact is good, replace BCM.

18. On all models, if BCM displays Hi with resume/accel switch depressed and Lo with resume/accel press released, enter BCM diagnostics and select BCM output test BO01.

19. With ignition switch in Run position and cruise switch in On position, BCM display and vent valve solenoid should both cycle. (A clicking noise should be heard at vent valve solenoid).

Fig. 14 Code B672:

20. If vent valve solenoid does not cycle (clicking noise is not heard) refer to code B672, Fig. 14.

21. If vent valve solenoid cycles (clicking noise is heard) enter BCM diagnostics and select BCM output test BO02.

22. With ignition switch in Run position and cruise switch in On position, BCM display and vacuum valve solenoid should both cycle.

23. If vacuum valve solenoid does not cycle, refer to code B673.

24. If vacuum valve cycles, start engine and run for 2 minutes, turn engine off, turn ignition switch to Run position, enter BCM diagnostics and select BCM override test BS05.

25. Vary override cycle from 0 to 99 and back to 0.

26. If cruise control servo pulls fully in and then releases, replace BCM.

27. If cruise control servo does not pull all the way in and then release, check vacuum source and hoses for leaks, kinks or restrictions and check cruise control servo for mechanical binding. If vacuum source and hoses are satisfactory and there is no binding, replace cruise control servo.