Cooling Fan Inoperative
Cooling Fan Inoperative (w/ LFA)
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 provides an overview of each diagnostic category.
Circuit/System Description
The hybrid engine cooling fan system consists of two electrical cooling fans, two resistors, three engine control module (ECM) fan output control drivers, and five fan relays. The relays are arranged in a series/parallel configuration that allows the ECM to operate the fans at low, medium, or high speed depending on engine cooling requirements. The ECM controls the five relays by grounding the relay control circuits.
During low speed operation, the ECM supplies the ground path for the low fan relay control circuit. This energizes the low fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the de-energized fan control relay, through the right cooling fan in-line resistor, and through the right cooling fan. The result is a series circuit with both fans running at low speed.
During medium speed operation the ECM grounds one control circuit that energizes a bank of three relays consisting of the FAN Mid 1 relay, the fan control relay, and the FAN Mid 2 relay. When these three relays are energized the Mid 1 relay supplies battery voltage to the left cooling fan through the left cooling fan resistor. A ground path is provided for the left fan through the energized fan control relay. At the same time the Mid 2 relay is energized which applies battery voltage to the right cooling fan through the right cooling fan resistor. The result is a parallel circuit where each fan has voltage applied through a resistor which causes each fan to operate at reduced speed.
During high speed operation the ECM grounds all three relay control circuits which activates all five relays. This allows full battery voltage to be applied to the right cooling fan from the high fan relay, and full battery voltage to be applied to the left fan from the low fan relay. The left fan is grounded through the fan control relay. In this arrangement each fan has full battery voltage applied and each fan has its own ground path. The result is a parallel circuit with both fans running at high speed.
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.
Diagnostic Aids
The ECM has the capability of providing command to the fan relays even while a scan tool output control is being used. Always refer to the fan control command parameters on the scan tool to know which fans are being commanded ON by the ECM.
Reference Information
Schematic Reference
Engine Cooling Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views
Description and Operation
Cooling Fan Description and Operation (w/o LFA) (Description and Operation)Cooling Fan Description and Operation (w/ LFA) (Description and Operation)
Electrical Information Reference
* Circuit Testing
* Connector Repairs
* Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Special Tools
Control Module References
Circuit/System Verification
1. Verify that the following DTCs are not set: P0480, P0481, or P0482.
• If any of the DTCs are set, repair the DTC first.
2. Ignition ON, command high and low speed fans ON and OFF with a scan tool. Observe to verify that the fans turn ON and OFF when changing between the commanded states.
Circuit/System Testing
Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
1. Ignition OFF, disconnect the fan control relay.
2. Ignition ON, activate the low cooling fan using the Relay 1 command on a scan tool. The fan should be OFF.
• If the fan is activated, test the left fan ground circuit for a short to ground.
3. Ignition OFF, disconnect the remaining fan relays.
4. Connect a 30A fused jumper between the normally-open switch contact terminals at the fan control relay connector in order to complete the left fan ground circuit. Leave this jumper in place for the remainder of this procedure.
5. One at a time, connect a 30A fused jumper between the positive terminal at the battery and the fan voltage supply circuit terminal at each relay connection and verify the appropriate fan activation.
• If the appropriate fan does not activate, test the fan voltage supply circuit for a short to ground or open/high resistance. If the circuit tests normal, test the fan ground circuit for open/high resistance. If the circuits test normal, replace the fan.
6. Ignition ON, connect a 30A fused jumper between the relay switch voltage supply circuit terminal and the fan voltage supply circuit terminal at the low speed and then the high speed relay connections and verify the appropriate fan activation.
• If the appropriate fan does not activate, test the relay switch voltage supply circuit for a short to ground or high resistance.
7. If the circuits and fans test normal, replace the relay.
Repair Instructions
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)
* Underhood Electrical Center or Junction Block Replacement
Repair Verification
Ignition ON, command the fan relay ON and OFF with a scan tool. Observe to verify that the appropriate fan turns ON and OFF with each command.