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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 838 (CRUISE CONTROL SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESCRUISE CONTROL INOPERATIVE/MALFUNCTIONING (L81)DIAGNOSTIC AIDS
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Aids

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Aids
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION: Refer to SIR CAUTION in Cautions and Notices.

Disable the inflatable restraint steering wheel module when performing this diagnostic table. Refer to DISABLING & ACTIVATING AIR BAG SYSTEM in SIR.

Perform the following in order to avoid misdiagnosis:

  • Inspect for proper adjustment of the stop lamp switch. Refer to Stop Lamp Switch Adjustment in Lighting Systems.
  • Inspect for proper adjustment of the cruise control release switch. Refer to Cruise Release Switch Adjustment .
  • Inspect for proper operation of the stop lamps. Refer to Exterior Lighting Systems Description and Operation in Lighting Systems.
  • Observe the Cruise Set/Coast and Cruise Resume/Accel parameters in the scan tool ECM General Info - Inputs data list while rotating the steering wheel to both steering stops and pressing and holding the steering wheel control switches. This will eliminate the possibility of a internally open or shorted inflatable restraint steering wheel module coil.
  • Ensure that the set/coast switch or the resume/accel switch are not stuck in the engaged position.
  • Electromagnetic interference on the vehicle speed sensor signal circuit may cause erratic cruise control operation.

For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.