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 Descriptors

DTC P0480: Cooling Fan Relay 1 Control Circuit

DTC P0481: Cooling Fan Relay 2 Control Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Low Speed Cooling Fan Relay Control Circuit for Cool/Fan 1 Relay 28

P0480

P0480

P0480

--

Low Speed Cooling Fan Relay Coil Voltage Supply Circuit for Cool/Fan 1 Relay 28

P0480

P0480

P0480

--

High Speed Cooling Fan Relay Control Circuit for Cool/Fan 2 Relay 30

P0481

--

P0481

--

High Speed Cooling Fan Relay Coil Voltage Supply Circuit Cool/Fan 2 Relay 30

P0481

P0481

P0481

--

High Speed Cooling Fan Relay Control Circuit for Cool/Fan SER/PAR Relay 29

P0481

--

P0481

--

Series/Parallel Relay Coil Voltage Supply Circuit for Cool/Fan SER/PAR Relay 29

P0481

P0481

P0481

--

Circuit/System Description

The engine control module (ECM) commands the fans ON in high speed or low speed. In low speed, the fans are configured in series. In high speed, the fans are configured in parallel.

In low speed operation, the ECM applies ground to the coil side of the low speed fan relay, which is the cool/fan 1 relay 28. Voltage is applied directly to the left cooling fan through the switch side of the low speed fan relay. The right fan is connected in series to the left fan through the series/parallel relay, which is cool/fan SER/PAR relay 29, so that both fans operate at low speed.

In high speed operation, the ECM applies a ground to the coil side of the low speed fan relay, the series/parallel relay, and the high speed fan relay, which is the cool/fan 2 relay 30. Voltage is applied directly to the right cooling fan through the switch side of the high speed fan relay. The left cooling fan obtains voltage through the low speed fan relay and ground through the series/parallel relay.

When the ECM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding a fan relay OFF, the voltage of the control circuit should be high, near battery voltage.

Conditions for Running the DTC

    • The ignition is ON.
    • The system voltage is between 9-18 volts.
    • The relay control circuit is transitioned from OFF to ON, or ON to OFF.

Conditions for Setting the DTC

    • An improper voltage level has been detected on the cooling fan relay control circuit.
    • The condition must be present for a minimum of 30 seconds.

Action Taken When the DTC Sets

DTCs P0480 and P0481 are Type B DTCs.

Conditions for Clearing the DTC

DTCs P0480 and P0481 are Type B DTCs.

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

  1. Verify with a scan tool that the ECM is not commanding fan relay activation.
  2. Ignition ON, command each relay ON and OFF with a scan tool. Feel or listen to verify that each relay turns ON and OFF with each command.
  3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

  1. Ignition OFF, disconnect the series/parallel relay, which is cool/fan SER/PAR relay 29.
  2. Connect a 30A fused jumper between the normally-open switch contact terminals 30 and 87 the series/parallel relay connector in order to complete the fan ground circuit. Leave this jumper in place for the remainder of this procedure.
  3. Ignition OFF, disconnect the affected relay.
  4. Verify that a test lamp does not illuminate between B+ and the affected relay control circuit terminal 85.
  5. Remove the test lamp.
  6. Command the affected relay ON with a scan tool. Verify the scan tool Relay Control Ckt. Short Volts Test Status Parameter is OK.
  7. If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  8. Install a 3A fused jumper wire between the control circuit terminal 85 and B+. Command the affected relay ON with a scan tool. Verify the scan tool Relay Control Ckt Short Volts Test Status Parameter is Fault.
  9. If not the specified value, test the control circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  10. Remove the 3A fused jumper wire.
  11. Connect a 30A fused jumper between the positive voltage terminal at the battery and the fan voltage supply circuit terminal at the affected relay connector and verify fan activation.
  12. Ignition ON, connect a 30A fused jumper between the relay switch voltage supply circuit terminal 30 and the fan voltage supply circuit terminal 87 at the affected relay connector and verify fan activation.
  13. If the fan does not activate, test the affected relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.
  14. Ignition ON, verify that a test lamp illuminates between the affected relay coil voltage supply circuit terminal 86 and ground.
  15. If the test lamp does not illuminate, test the affected relay coil voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.
  16. If all circuits and the ECM test normal, replace the affected relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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