• | 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 | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Cooling Fan Relay 1 Control Circuit for the Fan 1 Relay | P0480 | P0480 | P0480 | -- |
FAN 1 Relay Coil Voltage Supply Circuit | P0480 | P0480 | P0480 | -- |
Cooling Fan Relay 2 and 3 Control Circuit for the Fan 2 and FAN 3 Relays | P0481 | P0481 | P0481 | -- |
FAN 2 and FAN 3 Relays Coil Voltage Supply 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. 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, which is the FAN 2 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, the series/parallel relay, and the high speed relay. 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. If the ECM detects that the actual voltage of the relay control circuit is different than the expected voltage, DTC P0480 or P0481 will set and the affected ECM driver will be disabled.
• | 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. |
• | An improper voltage level has been detected on the cooling fan relay control circuit. |
• | The condition must be present for a minimum of 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
Verify cooling fan operation using the scan tool commands listed below:
• | Fan Relay 1 ON--Both fans run at low speed. |
• | Fan Relays 2 and 3 ON--The right fan runs at high speed, the left fan is OFF. |
• | Fan Relays 1, 2 and 3 ON--Both fans run at high speed. |
• | FAN 1 relay |
• | FAN 2 relay |
• | FAN 3 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 LO relay, use the scan tool Fan Relay 1 command. |
• | For the FAN CNTRL and FAN HI 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. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for ECM replacement, setup, and programming |