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Home >> Hummer >> 2010 >> H3 Base, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 23 (Battery, Charging System And Starting System) >> Diagnostic Information and Procedures >> DTC P0621 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2010 GMC Canyon and 2010 Chevrolet Colorado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Verify that a test lamp illuminates between the generator B+ terminal AX2 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  2. Ignition OFF, disconnect the X1 harness connector at the generator.
  3. Ignition ON, test for less than 1 V between the control circuit terminal 1 and ground.
    • If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the GBCM.
  4. Engine running, test for greater than 3 V between the control circuit terminal 1 and ground.
    • If less than the specified range, test the control circuit for a short to ground, or an open/high resistance. If the circuit tests normal, replace the GBCM.
  5. If all circuits test normal, test or replace the generator.
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