For 1990-2009 cars

## DTC P0480 or P0481 w/single fan

### 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
--- | --- | --- | --- | ---
Relay Coil Ignition Circuit | P0480, P0481 | P0480, P0481 | -- | --
Relay Switch Ignition Circuit | 1 | 1 | -- | --
Fan Low Control Circuit | P0480 | P0480 | P0480 | --
Fan High or Fan Control Circuit | P0481 | P0481 | P0481 | --
Relay Controlled Output Circuit | 1 | 1 | 2 | --

1. Fans inoperative without a DTC.
2. Fans always ON without a DTC.

### Circuit/System Description

The engine control module (ECM) commands the fans ON in either high speed or low speed, depending on cooling requirements.

In low speed operation, the ECM supplies a ground to the coil side of the low speed fan relay. This energizes the coil and applies voltage directly to the cooling fan through the switch side of the low relay. The fan is connected in series to the cooling fan resistor causing the fan to operate at low speed.

In high speed operation, the ECM supplies a ground to the coil side of the fan high or fan control relay. When energized, the fan high or control relay applies voltage directly to the cooling fan through the switch side of the relay. The ECM commands the low speed fan relay OFF and the cooling fan receives full voltage and operates at high speed.

### Conditions for Running the DTC

• | The engine is running.

• | The ignition voltage is between 11-18 volts.

• | The engine speed is greater 400 RPM.

• | The DTCs run continuously once the above conditions are met.

### Conditions for Setting the DTC

The ECM detects that the commanded state of the driver and the actual state of the control circuit do not match for greater than 2 seconds.

### Action Taken When the DTC Sets

DTC P0480 and P0481 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTC P0480 and P0481 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Cooling Schematics

#### Description and Operation

Cooling System Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | 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. Ignition ON, command the appropriate fan relay ON and OFF with a scan tool. You should hear the relay click when commanded ON and OFF.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. 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 appropriate cooling fan relay.
2. Ignition ON, verify that a test lamp illuminates between the relay coil ignition circuit terminal 85 and ground.

⇒ | If the test lamp does not illuminate, test the relay coil ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay coil ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.

3. Connect a test lamp between the relay coil control circuit terminal 86 and B+.
4. Command the fan relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒ | If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the ECM.

⇒ | If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

5. If all circuits test normal, test or replace the relay.

### Component Testing

1. Ignition OFF, disconnect the cooling fan relay.
2. Test for 70-110 ohms between terminals 85 and 86.

⇒ | If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

⇒ | If not the specified range, replace the relay.

4. Install a 20 A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 Ω between terminals 30 and 87.

⇒ | If greater than the specified range, replace the relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

• | Control Module References for ECM replacement, setup, and programming