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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1555 (Battery, Charging System And Starting System - Non-Hybrid) >> Diagnostic Information and Procedures >> DTC P0621 (Diesel) >> Circuit/System Testing - Dual Generators (K76)

Circuit/System Testing - Dual Generators (K76)

WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 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 connectors at both generators.
  2. Ignition ON, engine OFF, test for less than 1 V between the signal circuit terminal 1 of either generator harness 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. Ignition OFF, connect the X1 harness connector at the auxiliary generator.
  5. Ignition ON, engine OFF, test for less than 1 V between the signal circuit terminal 1 of the primary generator harness and ground.
    • If greater than the specified range, replace the auxiliary generator.
  6. Engine running, test for greater than 3.5 V between the signal circuit terminal 1 and ground.
    • If less than the specified range, replace the auxiliary generator.
  7. If all circuits test normal, test or replace the generator.
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