Circuit/System Testing

2006 Isuzu Ascender S, 5.3 M, 4WDSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2008 Isuzu Ascender, 2008 GMC Envoy, and 2008 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
IMPORTANT: In order to avoid misdiagnosis, inspect for the following:
  1. Ignition OFF, disable the SIR system. Refer to SIR Disabling and Enabling .
  2. Disconnect the turn signal multifunction switch harness connector X4.
  3. Ignition ON, verify the Cruise Control On/Off Switch parameter displays Off.
    • If the Cruise Control On/Off Switch parameter displays On, test the cruise ON switch signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Test for B+ between the turn signal multifunction switch harness connector X4 terminal A and ground.
    • If the reading is less than specified, test the cruise control switch voltage supply circuit for an open or high resistance.
  5. Connect a 3-amp fused jumper between terminals A and B of the turn signal multifunction switch harness connector X4. Verify the Cruise Control On/Off Switch parameter displays On.
    • If the Cruise On/Off Switch parameter displays Off, test the cruise control ON switch signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
  6. Verify the Cruise Control Resume/Accel. Switch parameter displays Off.
    • If the Cruise Control Resume/Accel. Switch parameter displays On, test the cruise control resume/accel. switch signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  7. Connect a 3-amp fused jumper between terminals A and C of the turn signal multifunction switch harness connector X4. Verify the Cruise Control Resume/Accel. Switch parameter displays On.
    • If the Cruise Resume/Accel. Switch parameter displays Off, test the cruise control resume/accel. switch signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
  8. Verify the Cruise Control Set/Coast Switch parameter displays Off.
    • If the Cruise Control Set/Coast Switch parameter displays On, test the cruise control set/coast switch signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  9. Connect a 3-amp fused jumper between terminals A and D of the turn signal multifunction switch harness connector X4. Verify the Cruise Control Set/Coast Switch parameter displays On.
    • If the Cruise Control Set/Coast Switch parameter displays Off, test the cruise control set/coast switch signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
  10. If all circuits test normal, replace the cruise control switch.
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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.