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 Descriptor

DTC P0480: Cooling Fan 1 Control Circuit Malfunction
DTC P0481: Cooling Fan 2 Control Circuit Malfunction

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage
--- | --- | --- | ---
Low Speed Cooling Fan Relay Control Circuit | P0480 | P0480 | P0480
Low Speed Cooling Fan Relay Coil Voltage Supply Circuit | P0480 | P0480 | P0480
High Speed Cooling Fan Relay Control Circuit | P0481 | P0481 | P0481
High Speed Cooling Fan Relay Coil Voltage Supply Circuit | P0481 | P0481 | P0481

### Circuit/System Description

The engine control module (ECM) grounds the cooling fan relay control circuits through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line that is monitored by the ECM. When the ECM is commanding a component ON the voltage potential of the control circuit should be low, near 0 volts. When the ECM is commanding the control circuit to a component OFF the voltage potential of the circuit should be high near battery voltage. If the ECM detects that the actual state of the control circuit does not match the expected state, a DTC will set.

### Conditions for Running the DTC

• | The ignition is ON.

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

### Conditions for Setting the DTC

• | An imcorrect voltage level has been detected on the cooling fan relay control circuit.

• | The condition must be present for a minimum of 30 seconds.

### Action Taken when the DTC Sets

DTCs P0480 and P0481 are type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0480 and P0481 are type B DTCs.

### Reference Information

#### Schematic Reference

Engine Cooling Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References

### Circuit/System 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.

### Circuit/System Testing

1. Ignition OFF, disconnect the fan relay.
2. Ignition ON, verify that a test lamp does not illuminate between the earth terminal and a known ground.

⇒ | If the test lamp illuminates, test the control circuit for a short to voltage.

3. Ignition ON, Connect a test lamp between the control circuit terminal and a known ground.

Command the 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 control circuit for a short to voltage. If the circuit tests normal replace the ECM.

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

4. Connect a test lamp between the Battery + terminal and a known ground.

⇒ | If the test lamp does not illuminates, test the Battery + for a short to ground or an open/high resistance.

5. Connect a 30-A fusible link wire between the battery positive post and the fan voltage supply circuit terminal and verify fan activation.

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

6. If all circuits test normal replace the affected relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

### Repair Verification

Ignition ON, command the relay ON and OFF with a scan tool. Feel or listen to verify that the relay turns ON and OFF with each command.