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Home >> GMC >> 1993 >> Forward Control 4.3 Z, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 153 (Cruise Control System) >> Self-Diagnostic Tests >> Test SC-1A - Checking Speed Control System
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Test SC-1A - Checking Speed Control System

WARNING: This page is about a different car, the 1995 Plymouth Voyager, 1995 Plymouth Grand Voyager, 1995 Dodge Grand Caravan, 1995 Dodge Caravan, and 1995 Chrysler Town & Country. However, it is still accessible from the selected car via links, so may be relevant.
  1. Turn ignition on. Using DRB, monitor speed (cruise) control switch inputs. While observing DRB, press speed control switch on. If DRB does not display speed control switch ON, perform TEST SC-2A. If DRB displays speed control switch ON, while observing DRB, press set switch several times.
  2. If DRB does not display set switch PR and RE, replace speed control switch. Perform TEST SC-VER  . If DRB displays set switch PR and RE, while observing DRB, press resume switch several times. If DRB does not display resume switch PR and RE, replace speed control switch. Perform TEST SC-VER  .
  3. If DRB displays resume switch PR and RE, while observing DRB, press brake pedal several times. If DRB does not display brake switch PR and RE, perform TEST SC-3A  .
  4. If DRB displays brake switch PR and RE, while observing DRB, place gear selector in Drive. If DRB does not display Park/Neutral (P/N) switch D/R, perform test SC-4A. If DRB displays P/N switch D/R, go to next step.
  5. Turn ignition off. Disconnect speed control servo connector. Check connector for damaged, pushed out or miswired terminals. Repair as necessary. Perform TEST SC-VER  . If connector is okay, check resistance of speed control servo connector terminal No. 1, ground circuit (Black wire) using DRB in ohmmeter mode.
  6. If resistance is greater than 5 ohms, repair open in Black wire. Perform TEST SC-VER  . If resistance is less than 5 ohms, turn ignition on. Press speed control switch on. Using DRB in voltmeter mode, check voltage of speed control servo connector terminal No. 2, speed control brake switch output circuit (Dark Blue/Red wire).
  7. If voltage is less than 10 volts, perform TEST SC-1B. If voltage is greater than 10 volts, reconnect speed control servo connector. Start engine and idle for one minute. Turn engine off, leaving ignition on. Using DRB, actuate speed control servo solenoids. If throttle opens and closes, perform TEST SC-5A  .
  8. If throttle does not open and close, turn ignition off. Disconnect vacuum supply to speed control servo. Attach a vacuum gauge to disconnected hose and start engine. If vacuum gauge does not read manifold vacuum, repair leak or restriction in vacuum supply. Perform TEST SC-VER  .
  9. If vacuum gauge reads manifold vacuum, turn engine off. Observe vacuum gauge for 10 seconds. If vacuum does not hold for 10 seconds, replace vacuum reservoir. Perform TEST SC-VER  . If vacuum holds for 10 seconds, inspect throttle cable. If throttle cable is disconnected or damaged, repair as necessary. Perform TEST SC-VER  . If throttle cable is okay, replace speed control servo. Perform TEST SC-VER  .
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