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 provide 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

Cooling Fan Relay Control Circuit for Fan 1 Relay

P0480

P0480

P0480

--

Fan 1 Relay Coil Voltage Supply Circuit

P0480

P0480

P0480

--

Cooling Fan Relay Control Circuit for Fan 2 Relay

P0481

P0481

P0481

--

Fan 2 Relay Coil Voltage Supply Circuit

P0481

P0481

P0481

--

Circuit/System Description

One Cooling Fan-3 Relays

The engine cooling fan system consists of one electrical cooling fan, two resistors, and three fan relays. The relays are arranged in a configuration that allows the engine control module (ECM) to operate the fan at low, medium, or high speeds, depending on cooling requirements. These speeds are obtained by three separate circuits within the cooling fan. Each circuit contains a unique resistance value. The cooling fan and fan relays receive battery positive voltage from the underhood fuse block. The ECM controls the 3 relays by grounding the relay control circuit.

Two Cooling Fans-3 Relays

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 relay, which is relay 1. Voltage is applied directly to the left cooling fan through the switch side of the low speed relay. The right fan is connected in series to the left fan through the de-energized series/parallel relay 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 relay, which is relay 1, the series/parallel relay, and the high speed relay, which is relay 2. Voltage is applied directly to the right cooling fan through the switch side of the high speed relay. The left cooling fan obtains voltage through the low speed 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.

A vehicle equipped with the trailer package option will get 2 puller and 2 pusher electric fans. During low speed operation, all 4 electric fans will operate at low speed. During high speed operation, all 4 electric fans will operate at high speed.

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

P0480

The ECM detects an open circuit in the low speed cooling fan relay control circuit.

P0481

    • The ECM detects an open circuit in the high speed cooling fan relay control circuit.
    • The above condition is present for 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
    •  Electrical Center Identification Views

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs
    •  Probing Electrical Connectors
    •  Electrical Center Identification Views

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Verify the cooling fan operation using the scan tool commands listed below:

One Fan System

    • Fan relay 1 is ON, fan runs at low speed.
    • Fan relays 2 and 3 are ON, fan runs at medium speed.
    • Fan relays 1, 2, and 3 are ON, fan runs at high speed.

Two Fan System

    • Fan relay 1 is ON--Both fans run at low speed.
    • Fan relays 2 and 3 are ON--The right fan runs at high speed, the left fan is OFF.
    • Fan relays 1, 2 and 3 are ON--Both fans run at high speed.

Circuit/System Testing

  1. Ignition OFF, disconnect the 3 cooling fan relays listed below:
  2. • Fan 1 relay
    • Fan 2 relay
    • S/P fan relay
  3. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 85 of each relay and ground.
  4. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  5. Verify that a test lamp does not illuminate between the ignition circuit terminal 85 and the control circuit terminal 86 of each relay.
  6. If the test lamp illuminates, test the control circuit for a short to ground. If the circuit test normal, replace the ECM.
  7. Remove the test lamp.
  8. Ignition ON, command the affected relay ON using a scan tool. Verify the affected scan tool FC Relay Control Ckt. Short Volts Test Status parameter is OK.
  9. • For the Fan 1 relay, use the scan tool Fan Relay 1 command.
    • For the fan 2 and the S/P fan relays, use the scan tool Relay 2 and 3 command.
         ⇒If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM
  10. Install a 3A fused jumper wire between the control circuit terminal 86 and the ignition circuit terminal 85. Command the affected relay ON with a scan tool. Verify the scan tool Relay Control Ckt Short Volts Test Status parameter is Fault.
  11. If not the specified value, test the control circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  12. If all circuits and the ECM test normal, replace the affected relay.

Repair Verification

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.