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Cruise Control Isolation Test

WARNING: This page is about a different car, the 1995 Cadillac Seville, 1995 Cadillac Eldorado, and 1995 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

Cruise control isolation test is designed to isolate the individual functional systems within the cruise control system. Before performing test procedures, perform self-diagnostics, record and diagnose any trouble codes. See ENTERING SELF-DIAGNOSTICS and DISPLAYING TROUBLE CODES in the appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section.

TESTS W/CODES - Eldorado

TESTS W/CODES - 4.6L - Concours

TESTS W/CODES - 4.9L - DeVille

TESTS W/CODES - 4.6L - Seville

Inspect cruise control servo throttle cable, cruise brake switch and Viscous Converter Clutch (VCC) brake switch for proper adjustment. Inspect vacuum hoses for kinks, leaks or restrictions.

  1. Slide cruise control switch to OFF position. PCM input PI82 display should read LO. If display does not read LO, check for short to voltage in circuits No. 86 (Brown wire) and No. 397 (Gray wire). Repair shorted wire(s) as necessary.
  2. Slide cruise control switch to ON position. PCM input PI82 display should read HI. If display does not read HI, Check fuse D5. Replace fuse, if necessary. Check for open in circuits No. 239 (Pink wire), No. 241 (Brown wire), and No. 397 (Gray wire). Repair wire(s) as necessary. Check circuits No. 86 (Brown wire), No. 239 (Pink wire), No. 241 (Brown wire), and No. 397 (Gray wire) for short circuit to ground. Repair wire(s) as necessary
  3. Leave cruise control switch on and select PCM input PI70. Depress brake pedal. PCM input PI70 display should read LO. If display does not read LO, check cruise brake switch adjustment. Adjust switch, if necessary. Check for short to voltage in circuit No. 86 (Brown wire). Repair short, if necessary.
  4. Release brake pedal. PCM input PI70 display should read HI. If display does not read HI, check cruise brake switch for adjustment or defect. Replace or adjust switch, if necessary. Check for open in circuits No. 86 (Brown wire) and No. 397 (Gray wire). Repair wire(s) as necessary.
  5. Leave cruise control switch on and select PCM input PI71. Depress brake pedal. PCM input PI71 display should read LO. If display does not read LO, see code P090 in PCM TROUBLE CODES table in the appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section.
  6. Release brake pedal. PCM input PI71 display should read HI. If display does not read HI, see code P090 in PCM TROUBLE CODES table.
  7. Leave cruise control switch on and select PCM input PI84. Slide cruise control switch to RESUME/ACCEL position. PCM input PI84 display should read HI. If display does not read HI, check for open in RESUME/ACCEL switch. Replace switch, if defective. Check for open in circuit No. 87 (Gray/Black wire). Repair wire, if necessary.
  8. Release cruise control switch. PCM input PI84 display should read LO. If display does not read LO, check for shorted RESUME/ACCEL switch. Replace switch, if defective. Also check for short to voltage in circuit No. 87 (Gray/Black wire).
  9. Depress SET/COAST button. PCM input PI84 display should read LO. If display does not read LO, check circuit No. 84 (Dark Blue wire) and circuit No. 87 (Gray/Black wire) for short to voltage. If Dark Blue and Gray/Black wires are okay, replace multifunction lever.
  10. Select PCM input PI83 and leave cruise control switch on. Depress SET/COAST button. PCM input PI83 display should read HI. If display does not read HI, check for open in cruise SET/COAST switch. Replace switch, if defective. Check for open in circuit No. 84 (Dark Blue wire). Repair wire, if necessary
  11. Release SET/COAST button. PCM input PI83 display should read LO. If display does not read LO, check for short in SET/COAST switch. If defective, replace switch. Check for short to voltage in circuit No. 84 (Dark Blue wire). Repair wire, if necessary.
  12. Slide cruise control switch to RESUME/ACCEL position. PCM input PI83 display should read LO. If display does not read LO, check circuit No. 84 (Dark Blue wire) and circuit No. 87 (Gray/Black wire) for short to voltage to each other. If Dark Blue and Gray/Black wires are okay, replace multifunction lever.
  13. Select PCM input P186. Depress brake pedal. PCM input P186 should read LO. If display does not read LO, brake switch may be misadjusted or defective. If switch is okay, check for short to voltage in circuit No. 847 (Gray wire).
  14. Release brake pedal. PCM input P186 should read HI. If display does not read HI, brake switch may be misadjusted or defective. If switch is okay, check for open or short to ground in circuits No. 741 (Brown wire) or No. 847 (Gray wire). If all results are normal, go to CRUISE CONTROL OUTPUT TEST.
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