• | 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. |
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 | -- |
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.
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.
• | 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. |
The ECM detects an open circuit in the low speed cooling fan relay control circuit.
• | The ECM detects an open circuit in the high speed cooling fan relay control circuit. |
• | The above condition is present for 30 seconds. |
DTCs P0480 and P0481 are Type B DTCs.
DTCs P0480 and P0481 are Type B DTCs.
Cooling Fan Description and Operation
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Control Module References for scan tool information
Verify the cooling fan operation using the scan tool commands listed below:
• | 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. |
• | 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. |
• | 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. |
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.