Circuit/System Testing

2006 Isuzu Ascender S, 5.3 M, 4WDSECTION Circuit/System Testing
WARNING: This page is about a different car, the 2007 Isuzu Ascender, 2007 GMC Envoy, 2007 Chevrolet TrailBlazer, and 2007 Buick Rainier. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the fan clutch at the shroud.
  2. Measure between the low reference circuit terminal and ground for less than 3 ohms.
    • If more than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the control module.
  3. Ignition ON, measure between the 5-volt reference and the low reference circuit terminals for 4.8-5.2 volts.
    • If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the control module.
    • If more than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the control module.
  4. Install jumper wires in the 5-volt reference and low reference circuits between the harness and pigtail connectors at the shroud.
  5. Measure DC voltage between the signal circuit terminal at the sensor pigtail connector and the 5-volt reference circuit jumper wire terminal.
  6. Ignition ON, rotate the fan by hand. The voltage should toggle between approximately 5 volts and 0 volts.
    • If the voltage does not toggle correctly, test the 3 circuits in the pigtail harness for a short to ground, a short to voltage or an open/high resistance. If the circuits test normal, replace the clutch.
  7. Leave the jumpers from the previous step in place. Measure voltage between the signal circuit terminals at the harness and pigtail connectors at the shroud.
  8. Rotate the fan by hand. The voltage should toggle between approximately 5 volts and 0 volts.
    • If the voltage does not toggle correctly, test the signal circuit for a short to ground or a short to voltage. If the circuit tests normal, replace the control module.
  9. If all circuits and the speed sensor test normal, replace the engine control module (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.