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OBD-II Trouble Shooting Got a code reader? Find out what your GM car's Check Engine light is trying to tell you (and then turn Check Engine light off).

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Old 11-09-2009, 11:29 PM   #1
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Default P0480


Cooling Fan Relay 1 Control Circuit

Output driver modules (ODMs) are used by the PCM to turn on many of the current-driven devices that are needed to control various engine and transaxle functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the devices which the PCM is commanding on. Unlike the quad driver modules (QDMS) used in prior model years, ODM’* have the capability of diagnosing each output circuit individually. DTC P0480 indicates an improper voltage level has been detected on the output circuit, which controls the fan 1 relay.

  • The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test was run and failed.
  • The PCM will store the conditions, which were present when the DTC set as Freeze Frame Failure Records Data.
  • An improper voltage level has been detected on the fan 1 relay control circuit.
  • The voltage conditions are present for at least 30 seconds.
Check for the following conditions:
  • A faulty connection at the PCM – inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connections.
  • Inspect the wiring harness for damage.
  • If the harness appears to be okay, disconnect the PCM, turn the ignition ON and observe a DMM connected between the fan 1 relay driver circuit and ground at the PCM harness connector while moving connectors and wiring harnesses related to the fan 1 relay. A change in voltage will indicate the location of the fault.
  • With the ignition off, disconnect the relay. Turn ignition ON (DO NOT START). Probe the coil feed circuit of the relay with a test lamp connected to ground.
    • Does the test lamp illuminate?
      • NO - Check the fuse. If blow check each branch of the circuit for a short and repair. If problem found and repaired, clear DTC.
      • YES – A scan tool will be needed to check the command ON and OFF with the control circuit.
  • Also test the control circuits of the rely for a short to voltage or an open. If problem found, repair.
  • Replace the relay if no shorts or an open on the feed circuit or control circuit is found.
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