• | 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 |
---|---|---|---|---|
Low Speed Cooling Fan Relay Control Circuit for Fan 1 Relay 33 | P0480 | P0480 | P0480 | -- |
Fan 1 Relay 33 Coil Voltage Supply Circuit | P0480 | P0480 | P0480 | -- |
High Speed Cooling Fan Relay Control Circuit for Fan 2 Relay 31 | P0481 | -- | P0481 | -- |
Fan 2 Relay 31 Coil Voltage Supply Circuit | P0481 | P0481 | P0481 | -- |
High Speed Cooling Fan Relay Control Circuit for Fan 3 Relay 32 | P0481 | -- | P0481 | -- |
Fan 3 Relay 32 Coil Voltage Supply Circuit | P0480 | P0480 | P0480 | -- |
The engine cooling fan system consists of 2 electrical cooling fans and three fan relays. The relays are arranged in a series/parallel (S/P) configuration that allows the powertrain control module (PCM) or engine control module (ECM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.
During low speed operation, the PCM supplies the ground path for the fan 1 relay 33, which is low speed fan relay, through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the fan 1 fuse 27 through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the fan 3 relay 32, which is series/parallel relay, and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation, the PCM or ECM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. The PCM supplies a ground path for the series/parallel and the fan 2 relay 31, which is high speed fan relay, through the high speed cooling fan relay control circuit. This energizes the high speed fan relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time, the series/parallel relay coil is energized closing the relay contacts, and provides battery positive voltage from the fan 2 fuse on the cooling fan motor supply voltage circuit, to the right cooling fan. During high speed fan operation, both engine cooling fans have their own ground path. The result is a parallel circuit with both fans running at high speed.
When the request for fan activation is withdrawn, the fan may not turn OFF until the ignition switch is moved to the OFF position or the vehicle speed exceeds approximately 10 mph. This is to prevent a fan from cycling ON and OFF excessively at idle.
• | 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 coding 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
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.
⇒ | If the test lamp is always ON, test the relay control circuit for a short to ground. If the circuit tests normal, replace the PCM. |
⇒ | 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 PCM. |
⇒ | 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. |
⇒ | 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. |
⇒ | 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. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for PCM replacement, setup, and programming |