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.

### Circuit/System Description

The engine control module (ECM) controls cooling fan operation in either high speed or low speed mode, depending on cooling requirements. To activate a fan, the ECM applies ground to the coil side of the applicable fan relay. This energizes the coil and applies voltage directly to the cooling fan through the switch side of the relay.

### Reference Information

#### Schematic Reference

Engine Cooling Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Cooling System Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Verify that DTCs P0480 and P0481 are not set.

⇒ | If any cooling system DTCs are set, repair the DTC first. Refer to DTC P0480 or P0481.

2. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.

⇒ | If the fan is commanded ON, diagnose the ECM first. Refer to DTC P0480 or P0481.

3. Ignition ON, observe that the fan is not activated.

### Circuit/System Testing

Important: The following tests must be performed on each cooling fan relay.

1. Ignition OFF, disconnect each cooling fan relay one at a time.
2. Ignition ON, observe that the cooling fans are not activated.

⇒ | If the fans are activated, test for a short to voltage in the relay controlled output circuit.

⇒ | If the fans are not activated, test for a short to ground in the relay coil control circuit.

3. If all circuits test normal, test or replace the cooling fan relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Relay Replacement