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Home >> Hummer >> 2008 >> H2 4D Utility Wagon >> Repair and Diagnosis >> External Pages >> Different car >> Section 319 (Engine Cooling System) >> Diagnostic Information and Procedures >> DTC P0480 or P0481 (without HP2) >> Circuit/System Testing

Circuit/System Testing

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  1. Ignition OFF, disconnect the 3 cooling fan relays listed below.
    • FAN LO relay
    • FAN CNTRL relay
    • FAN HI relay
  2. Ignition ON, verify that a test lamp illuminates between ground and the ignition circuit terminal 85 of each relay.
    • If the test lamp does not illuminate, test the ignition circuit for an open/high resistance.
  3. Set the DMM on the diode setting. Connect the black lead to ground. Connect the red lead of the DMM to a control circuit terminal listed below:
    • FAN LO Relay terminal 86
    • FAN CNTRL Relay terminal 86
    • FAN HI Relay terminal 86

      The DMM should display OL.

    • If less than the specified range, test the appropriate relay coil control circuit for a short to ground. If the circuit tests normal, replace the K20 ECM.
  4. Command the appropriate cooling fan relay ON and OFF with a scan tool. The DMM should transition from OL when commanded OFF to less than 1 V when commanded ON.
    • If the circuit voltage does not correspond to the specified values, test the control circuit for an open/high resistance or for a short to voltage. If the circuit tests normal, replace the K20 ECM.
  5. If all circuits test normal, test or replace the appropriate KR20 relay.
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