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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1301 (Battery, Charging System And Starting System) >> Diagnostic Information and Procedures >> DTC P0621 (Gasoline) >> Circuit/System Testing (Gasoline)

Circuit/System Testing (Gasoline)

WARNING: This page is about a different car, the 2009 GMC 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 X1 harness connector at the generator.
  2. Ignition ON, test for less than 1 V between the signal circuit terminal 1 and ground.
    • If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  3. Engine running, test for greater than 3.5 V between the signal circuit terminal 1 and ground.
    • If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
  4. If all circuits test normal, test or replace the generator.
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