• | 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 |
---|---|---|---|---|
Low Speed Cooling Fan Relay Control Circuit | P0480 | P0480 | P0480 | -- |
High Speed Cooling Fan Relay Control Circuit | P0481 | P0481 | P0481 | -- |
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
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.
• | Low speed fan relay terminal R69 |
• | High speed fan relay terminal R82 |
• | Fan 1 relay commands the low speed fan relay |
• | Fan 2 and 3 relays command the high speed fan relay |
⇒ | If the test lamp is always ON, test the relay control circuit for a short to ground. If the circuit tests normal, replace the ECM. |
⇒ | If the test lamp is always OFF, test the relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
• | Low speed fan relay terminal R70 |
• | High speed fan relay terminal R83 |
⇒ | 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. |
• | Low speed fan relay terminal R37 to R70 |
• | High speed fan relay terminal R80 to R83 |
⇒ | If the fan does not activate, test the affected relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary. |
• | Low speed fan relay terminal R68 |
• | High speed fan relay terminal R81 |
⇒ | If the test lamp does not illuminate, test the affected relay coil voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary. |
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.