For 1990-2009 cars

### 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 P0480: Cooling Fan Relay 2 Control Circuit

### Diagnostic Fault Information

Circuit | Short to Ground | OFF/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Low Speed Cooling Fan Relay Control Circuit | P0480 | P0480 | P0480 | --
High Speed Cooling Fan Relay Control Circuit | P0481 | P0481 | P0481 | --

### Circuit/System Description

The engine control module (ECM) can command the fans ON at high speed or low speed. The fan completes a series circuit at low speed and a parallel circuit at high speed.

The ECM will ground the relay control side of the low speed fan relay (relay 1) at low speed. The ECM directly supplies power to the left side cooling fan through the solenoid side of low speed relay. The right side cooling fan is connected in series to the left side fan through the de-energized series/parallel relay, so that both fans operate at low speed.

The ECM ground the relay control side of the low speed fan relay (relay 1), S/P relay and the high speed relay (relay 2) together at high speed. Applied power directly to the right side cooling fan through the solenoid of the high speed relay. By connecting the S/P relay, the left side cooling fan ground to obtain the voltage.

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 potential of the control circuit should be high, near battery voltage.

### Conditions for Running the DTC

• | The system voltage is between 9-18 volts.

• | Engine RPM is more than 400 RPM.

### Conditions for Setting the DTC

• | The ECM detects that the commanded state of the relay control circuit and the actual state do not match.

• | At least 20 times out of 25 tests.

### Action Taken When the DTC Sets

DTC P0480, P0481 are the type B DTC.

### Conditions for Clearing the DTC

DTC P0480, P0481 are the type B DTC.

### Reference Information

#### Schematic Reference

• | Engine Cooling Schematics

• | Power Distribution Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Electrical Center Identification Views

#### Description and Operation

• | Engine Control Module Description

• | Cooling System Description and Operation

#### Electrical Information

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

• | Probing Electrical Connectors

• | Electrical Center Identification Views

#### Scan Tool Reference

• | Scan Tool Output Controls

• | Scan Tool Data List

• | Scan Tool Data Definitions

#### Special Tools

J 43244 Relay Puller Pliers

### Circuit/System Verification

1. Turn the ignition switch OFF and disconnect S/P connector.
2. Connect a 30A fused jumper between the normally-open switch connection terminals R15 and R16 at the S/P fan relay connector to ensure circuit integrity of the fan ground circuit, and keep it in the proper circuit position.
3. Turn the ignition switch OFF and disconnect the affected relay.
4. Turn the ignition switch ON and connect a test lamp between the battery positive terminal and the affected relay control circuit listed below:

• | Low Speed Fan Relay Terminal R42

• | High Speed Fan Relay Terminal R22

5. Use the scan tool to command the affected relay ON and OFF. The test lamp should turn ON or OFF with the change of the commanded states.

• | Fan relay 1 commands the low speed fan relay.

• | Fan relays 2 and 3 command the high speed fan relay

⇒ | If the test lamp remains illuminated at all times, test for a short to ground in the relay control loop. If the circuit tests normal, replace the ECM.

⇒ | If the test lamp stays OFF all the time, test relay circuit for a short to voltage, an open or high resistance. If the circuit tests normal, replace the ECM.

6. Connect a 30 A fused jumper between the battery positive voltage terminal and the fan feed circuit terminal of the affected relay connector listed below, and verify the activation of the fan.

• | Low Speed Fan Relay Terminal R41

• | High Speed Fan Relay Terminal R21

⇒ | If the fan does not activate, test the fan feed circuit for a short to ground or open/high resistance. If the circuits test normal, replace the fan.

7. Turn the ignition switch OFF, connect a 30A fused jumper between the relay solenoid feed circuit terminal and the fan feed circuit terminal of the affected relay connector listed below, and verify the activation of the fan.

• | Low Speed Fan Relay Terminal R41

• | High Speed Fan Relay Terminal R21

⇒ | If the fan does not activate, test the affected relay solenoid feed 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.

8. Turn the ignition switch ON, and verify that the test lamp between the affected relay coil feed circuit terminal and ground is ON.

• | Low Speed Fan Relay Terminal R39

• | High Speed Fan Relay Terminal R19

⇒ | If the test lamp is OFF, test the affected relay coil feed 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.

9. If all circuits and the ECM test normal, replace the affected relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Fan Replacement

• | Relay Replacement

• | Underhood Electrical Center or Junction Block Replacement

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