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1988 Corvette: fuses..the cruise control module in the dast cluster

Customer Question

I have a 1988 Corvette/ the cruise control is not working(engaging) I''ve checked the cruise and lcd fuses and they are good and have power. I have also run a Servo Actuation test and that passed w/ flying colors. I suspect the cruise control lever/switch or the cruise control module in the dast cluster. PLEASE HELP!!       Thank You, XXXXX XXXXX
Submitted: 6 years ago.
Category: Chevy
Expert:  GM-Frank replied 6 years ago.

 

HelloCustomer

On your cruise control, one of the first checks is to be sure the brake switch and or clutch switch is adjusted correctly, as they will automatically dis-engage cruise if not in the correct adjustment. Let's check the easy stuff first.

  1. Turn ignition switch to ON position. Turn the Cruise switch to the ON position
  2. Connect test light to ground.
  3. Probe at both sides of brake switch connector (see schematic diagrams for color codes). Lamp should illuminate on one wire.
  4. If lamp did not illuminate on either wire, check wiring circuit and fuses going to the switch.
  5. Check switch adjustment by putting test lamp on wire that did not light in step 3. Depress brake pedal 1/8 - 1/2 inch. Light should go on.
  6. If lamp did not illuminate in step 5, and connections are good, replace the cruise control brake switch.

The clutch switch is used on vehicles equipped with manual transmission. When the clutch pedal is depressed, the cruise function is disconnected and will remain so after the pedal is released.

Below is the complete diagnostic for the cruise.

When performing the following tests, refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC DIAGRAMS for wiring diagram.

  1. Disconnect instrument cluster connector, turn ignition switch to Run position and cruise switch to Off position and measure voltage between terminals as follows:
    1. Measure between terminal D5 (orange wire) and ground.
    • If battery voltage is not available, check LCD fuse and orange wire (circuit 840) for an open.
    1. Measure between terminal C7 (gray/white wire) and ground.
    • If battery voltage is not available, replace multi-function lever.
    1. Place cruise switch in On position.
    2. Measure between terminal C7 (gray/white wire) and ground.
    • If battery voltage is not available, check cruise fuse, cruise switch, pink/black wire (circuit 539) and gray/white wire (circuit 397) for an open.
    1. Measure between terminal C12 (gray/black wire) and ground.
    • If battery voltage is not available, check TCC/cruise brake switch, cruise control clutch switch, gray/white wire (circuit 397) light blue wire (circuit 987) and/or gray/black wire (circuit 87) for an open.
    1. Measure between terminal C13 (dark blue wire) and ground.
    • If there is voltage available, replace multi-function lever.
    1. Depress set switch.
    2. Measure between terminal C13 (dark blue wire) and ground.
    • If battery voltage is not available, check set switch and dark blue wire (circuit 84) for an open.
    1. Measure between terminal C11 (dark green wire) and ground.
    • If voltage is available, replace multi-function lever.
    1. Place cruise switch in Resume/Accel position.
    2. Measure between terminal C11 (dark green wire) and ground.
    • If battery voltage is not available, check cruise switch and dark green wire (circuit 83) for an open.
  1. If battery voltage was available in steps a, b, d, e, h and k and there was no voltage available in steps f and i, disconnect instrument cluster connector and measure resistance as follows:
    1. Measure between terminal D3 (black/white wire) and ground.
    • If resistance is shown, check black/white wire (circuit 153) and black wire (circuit 150) for an open.
    1. Measure between terminal D9 (light green wire) and ground.
    • If reading is not 30-55 ohms, check vacuum valve coil in cruise control servo, light green wire (circuit 402) and black wire (circuit 150).
    1. Measure between terminal D8 (dark blue wire) and ground.
    • If reading is not 30-55 ohms, check vent valve coil in cruise control servo and dark blue wire (circuit 403).
    1. Measure between terminals C10 (tan wire) and C14 (dark blue/white wire).
    • If reading is not 15-30 ohms, check servo position sensor, dark blue/white and light blue/black wires (circuit 399) and tan wire (circuit 398).
    1. Measure between terminal C10 (tan wire) and ground.
    • If reading is not infinite, check servo position sensor and tan wire (circuit 398) for a short to ground.
  1. If reading was 0 ohms in step a, 30-55 ohms in steps b and c, 15-30 ohms in step d and infinite ohms in step e, disconnect cruise control servo connector and connect fused jumper between terminal C (black wire) of servo and ground and between terminal A (dark blue wire) of servo and battery and run engine for 1 minute, then turn engine off.
    1. Connect fused jumper between terminal E (light green wire) and battery.
    • If vacuum does not pull servo all the way in, proceed to step 4.
    1. Remove jumper from between terminal E and battery.
    • If vacuum does not hold servo all the way in, proceed to step 4.
  1. Plug vacuum release port and repeat step 3.
  2. If vacuum now holds servo all the way in, repair or replace brake switch or the hose to it.
  3. If test still fails, replace cruise control servo.

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This information should get you to your problem. I do agree, sounds like the lever/switch.

Take Care

Frank

Customer: replied 6 years ago.
Thanks GM-Frank, The test you sent me I have already tried as I have All-Data here at my shop, I was hoping you might have some other insight on this problem. I will go over the 1st test again and see if I missed anything.
Thank You
Expert:  GM-Frank replied 6 years ago.

 

OK Rey,

I understand. Way back, I had a tester for these I bought from Snap-on, but that won't help you on this one. I know the manual tests are a bit of a pain, but they do give us apretty good set of tests for the switch. I would check the voltages at the lever and see what you come up with.

Frank

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GM-Frank
GM-Frank
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37 Years Automotive Diagnosis and Repair. 25 Years of General Motors Dealer Experience