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) commands the fans ON in either high speed or low speed, depending on cooling requirements. In low speed, both fans are turned ON at a reduced speed. High speed has both fans turned ON at full speed.

In low speed operation, the ECM applies ground to the coil side of the low speed fan relay. This energizes the coil and applies voltage directly to the main cooling fan through the switch side of the low relay. The main fan is connected in series to the auxiliary cooling fan through the de-energized series/parallel fan control relay. The series circuit operates both fans at low speed.

In high speed operation, the ECM applies a ground to the coil side of the low speed fan relay, the fan control relay, and the high speed fan relay. When energized, the high speed fan relay applies voltage directly to the auxiliary cooling fan through the switch side of the relay. Simultaneously, the low speed fan relay and the fan control relay provide ignition voltage and a direct path to ground for the main cooling fan. With both fans connected in a parallel circuit, each fan receives full voltage and operates at high speed.

### 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. Ignition ON, observe the DTC information with a scan tool. Verify that DTCs P0480, P0481, or P0482 are not set.

⇒ | If any of the above DTCs are set, refer to DTC P0480, P0481, or P0482.

2. Ignition ON, command the fan relays ON and OFF with a scan tool. The cooling fans should operate with the appropriate commands.
3. Ignition ON, command the appropriate fan relay ON and OFF with a scan tool. Verify that the fans turn ON and OFF when changing between the commanded states.

### Circuit/System Testing

1. Ignition OFF, disconnect the cooling fan relays.
2. Connect a 30 A fused jumper between the relay switch circuit terminal 30 and the ground circuit terminal 87 at the series/parallel fan control relay connector. This will complete the main fan ground circuit. Leave this jumper in place for the remainder of this procedure.

Note: The following test must be performed on both the high speed fan relay circuit and the low speed fan relay circuit.

3. Ignition ON, verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.

⇒ | If the test lamp does not illuminate, test the appropriate relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the relay.

Note: The following test must be performed first on the high speed fan relay circuit and next on the low speed fan relay circuit. Leave the jumper connected to the low speed fan relay circuit for the next test.

4. Connect a 30A fused jumper between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87. Verify the appropriate fan is activated

⇒ | If the appropriate fan does not activate, test the relay controlled output circuit for a short to ground or an open/high resistance. If the circuit tests normal, test the fan ground circuit for an open/high resistance. If the circuit tests normal, replace the fan.

5. Install the fan control relay. Verify both fans activate at low speed.

⇒ | If both fans do not activate, test the relay controlled output circuit terminal 87A of the fan control relay for a short to ground or an open/high resistance.

6. 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 Ω between terminals 85 and 86.

⇒ | If 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. Test for less than 2 Ω between the relay terminals 30 and 87A.

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

5. Install a 20 A fused jumper wire between relay terminal 85 and B+. Install a jumper wire between the 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

• | Engine Coolant Fan Replacement