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Circuit/System Testing

WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the TCM harness connector.
  2. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal 25 and ground.
    • 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 ECM.
    • If greater than the specified range, test the 5 volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  3. If all the circuits test normal, replace the TCM.
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