Circuit/System Testing

2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2008 Chevrolet Malibu Classic. However, it is still accessible from the selected car via links, so may be relevant.
IMPORTANT: Electromagnetic interference (EMI) on the speed sensor signal circuit may cause erratic cruise control operation.
  1. Ignition OFF, remove the inflatable restraint steering wheel module. Refer to Inflatable Restraint Steering Wheel Module Replacement (Non-SS) or Inflatable Restraint Steering Wheel Module Replacement (SS) .
  2. Disconnect the harness connector at the steering wheel controls switch - left.
  3. Ignition ON, test for greater than 10 volts between the supply voltage circuit terminal 4 and ground.
    • If less than the specified range, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  4. Verify the scan tool Cruise Control Switch parameter is OFF.
    • If not the specified value, test the signal circuit terminal 5 for a short to voltage. If the circuit tests normal, replace the BCM.
  5. Ignition OFF, connect the harness connector at the steering wheel controls switch - left.
  6. Ignition ON, with the cruise control switch in the ON position, observe the scan tool Cruise Control Switch parameter. The parameter should display ON.
    • If not the specified value, test the signal circuit terminal 5 for a short to ground, a short to voltage or an open/high resistance. If the circuit tests normal, test or replace the steering wheel controls switch - left.
  7. Observe the scan tool Cruise Control Switch parameter while pressing the RES + portion of the cruise control switch. The parameter should display Resume.
    • If not the specified value, test or replace the steering wheel controls switch - left.
  8. Observe the scan tool Cruise Control Switch parameter while pressing the SET - portion of the cruise control switch. The parameter should display Set.
    • If not the specified value, test or replace the steering wheel controls switch - left.
  9. Observe the scan tool Cruise Control Switch parameter while pressing the Cancel portion of the cruise control switch. The parameter should display Cancel.
    • If not the specified value, test the cruise control cancel signal for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the steering wheel controls switch - left.
  10. If all circuits test normal, test or replace the ECM.
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When to See a Mechanic

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

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