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 provide an overview of each diagnostic category. |
DTC Descriptors
DTC P0480: Cooling Fan Relay 1 Control CircuitDTC P0481: Cooling Fan Relay 2 Control Circuit
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Cooling Fan Relay Control Circuit for Fan 1 Relay | P0480 | P0480 | P0480 | -- |
Fan 1 Relay Coil Voltage Supply Circuit | P0480 | P0480 | P0480 | -- |
Cooling Fan Relay Control Circuit for Fan 2 Relay | P0481 | P0481 | P0481 | -- |
Fan 2 Relay Coil Voltage Supply Circuit | P0481 | P0481 | P0481 | -- |
Circuit/System Description
One Cooling Fan-3 Relays
The engine cooling fan system consists of one electrical cooling fan, two resistors, and three fan relays. The relays are arranged in a configuration that allows the engine control module (ECM) to operate the fan at low, medium, or high speeds, depending on cooling requirements. These speeds are obtained by three separate circuits within the cooling fan. Each circuit contains a unique resistance value. The cooling fan and fan relays receive battery positive voltage from the underhood fuse block. The ECM controls the 3 relays by grounding the relay control circuit.
Two Cooling Fans-3 Relays
The engine control module (ECM) commands the fans ON in high speed or low speed. In low speed, the fans are configured in series. In high speed, the fans are configured in parallel.
In low speed operation, the ECM applies ground to the coil side of the low speed relay, which is relay 1. Voltage is applied directly to the left cooling fan through the switch side of the low speed relay. The right fan is connected in series to the left fan through the de-energized series/parallel relay so that both fans operate at low speed.
In high speed operation, the ECM applies a ground to the coil side of the low speed relay, which is relay 1, the series/parallel relay, and the high speed relay, which is relay 2. Voltage is applied directly to the right cooling fan through the switch side of the high speed relay. The left cooling fan obtains voltage through the low speed relay and ground through the series/parallel relay.
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 of the control circuit should be high, near battery voltage.
A vehicle equipped with the trailer package option will get 2 puller and 2 pusher electric fans. During low speed operation, all 4 electric fans will operate at low speed. During high speed operation, all 4 electric fans will operate at high speed.
Conditions for Running the DTC
| • | The ignition is ON. |
| • | The system voltage is between 9-18 volts. |
| • | The relay control circuit is transitioned from OFF to ON or ON to OFF. |
Conditions for Setting the DTC
P0480
The ECM detects an open circuit in the low speed cooling fan relay control circuit.
P0481
| • | The ECM detects an open circuit in the high speed cooling fan relay control circuit. |
| • | The above condition is present for 30 seconds. |
Action Taken When the DTC Sets
DTCs P0480 and P0481 are Type B DTCs.
Conditions for Clearing the DTC
DTCs P0480 and P0481 are Type B DTCs.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Cooling Fan Description and Operation
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Verify the cooling fan operation using the scan tool commands listed below:
One Fan System
| • | Fan relay 1 is ON, fan runs at low speed. |
| • | Fan relays 2 and 3 are ON, fan runs at medium speed. |
| • | Fan relays 1, 2, and 3 are ON, fan runs at high speed. |
Two Fan System
| • | Fan relay 1 is ON--Both fans run at low speed. |
| • | Fan relays 2 and 3 are ON--The right fan runs at high speed, the left fan is OFF. |
| • | Fan relays 1, 2 and 3 are ON--Both fans run at high speed. |
Circuit/System Testing
- Ignition OFF, disconnect the 3 cooling fan relays listed below:
- Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 85 of each relay and ground.
- Verify that a test lamp does not illuminate between the ignition circuit terminal 85 and the control circuit terminal 86 of each relay.
- Remove the test lamp.
- Ignition ON, command the affected relay ON using a scan tool. Verify the affected scan tool FC Relay Control Ckt. Short Volts Test Status parameter is OK.
- Install a 3A fused jumper wire between the control circuit terminal 86 and the ignition circuit terminal 85. Command the affected relay ON with a scan tool. Verify the scan tool Relay Control Ckt Short Volts Test Status parameter is Fault.
- If all circuits and the ECM test normal, replace the affected relay.
| • | Fan 1 relay |
| • | Fan 2 relay |
| • | S/P fan relay |
| ⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. |
| ⇒ | If the test lamp illuminates, test the control circuit for a short to ground. If the circuit test normal, replace the ECM. |
| • | For the Fan 1 relay, use the scan tool Fan Relay 1 command. |
| • | For the fan 2 and the S/P fan relays, use the scan tool Relay 2 and 3 command. |
| ⇒ | If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM |
| ⇒ | If not the specified value, test the control circuit for an open/high resistance. If the circuit tests normal, replace the ECM. |
Repair 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.
