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Home >> Hummer >> 2008 >> H3 Base, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 467 (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 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.

LLT Engine

  1. Verify that a test lamp illuminates between the G13 generator B+ terminal X2 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 harness connector X1 at the generator.
  3. Ignition ON, test for less than 1 V between the control circuit terminal 1 X1 and ground.
    • If greater than the specified range, test the control circuit signal for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Engine running, test for greater than 3.5 V between the control circuit terminal 1 X1 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 ECM.
  5. If the circuit tests normal, test or replace the generator.

LH2 or LC3 Engine

  1. Verify that a test lamp illuminates between the generator B+ terminal X2 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 harness connector X1 at the generator.
  3. Ignition ON, test for 4.5-5.5 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 ECM.
    • 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 ECM.
  4. If the circuits test normal, replace the generator.
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