GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0480: Cooling Fan Speed Output Circuit

Diagnostic Fault Information

Circuit

Short to Ground

High Resistance

Open

Short to Voltage

Signal Performance

Cooling Fan Speed Control Circuit

P0480

P0480

P0480

P0480

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Circuit/System Description

The engine cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated signal to the cooling fan speed control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the pulse width modulated signal. The cooling fan speed is affected by many different conditions and can be adjusted from 10-90 percent duty cycle. Ninety percent is considered high fan speed. When multiple cooling speed requests are received, the ECM uses the highest cooling fan speed of all the requests. During normal fan ON operation, the control circuit voltage will be low and near battery voltage when the fan is OFF.

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Circuit/System Verification

Engine running, command the cooling fan speed from 0-100 percent with a scan tool. The fan speed should transition with the commanded states.

Circuit/System Testing

Important: The Circuit/System Verification must be performed first or misdiagnosis may result.

  1. Ignition OFF, disconnect the connector from the cooling fan speed control module.
  2. Ignition OFF, install a test lamp between the cooling fan speed control circuit terminal 6 and B+. The lamp should be OFF.
  3. If the lamp is ON, test the cooling fan speed control circuit for a short to ground. If the circuit tests normal, replace the ECM.
  4. Ignition ON, command the cooling fan speed from 0-100 percent with a scan tool. The brightness of the lamp should change with the commanded states.
  5. If the lamp brightness does not change correctly, test the cooling fan speed control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  6. Ignition OFF, measure between the cooling fan speed control module ground circuit terminal 2 at the harness connector and ground for less than 1 ohm.
  7. If greater than the specified range, repair the module ground circuit for open/high resistance.
  8. Ignition OFF, verify that a test lamp illuminates between the B+ circuit terminal 3 and ground.
  9. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  10. Install appropriately fused jumpers between the cooling fan harness connector terminals 1 and 4 power and ground. The cooling fan should activate at full speed.
  11. If the cooling fan does not activate, replace the cooling fan.
  12. If the ECM, fan, and all circuits test normal, replace the cooling fan speed control module.

Repair Instructions

    •  Cooling Fan and Shroud Replacement
    •  Cooling Fan Control Module Replacement
    •  Control Module References for ECM replacement, setup, and programming

Repair Verification

Ignition ON, command the cooling fan speed from 0-100 percent with a scan tool. The fan speed should transition with the commanded states.