Cooling Fan Inoperative
Cooling Fan Inoperative
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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 engine control module (ECM) commands the fans ON in either high speed or low speed, depending on cooling requirements. In low speed, both fans are turned ON at a reduced speed. High speed has both fans turned ON at full speed.
In low speed operation, the ECM applies ground to the coil side of the fan 1 relay. This energizes the coil and applies voltage directly to the right cooling fan through the switch side of the fan 1 relay, which is fed by the fan 1 fuse. The right fan is connected in series to the left fan through the de-energized fan 2 relay so that both operate at low speed.
In high speed operation, the ECM applies a ground to the coil side of the fan 1 relay, the fan 2 relay , and the fan 3 relay. On the fan 3 relay, the energized coil closes the switch side of the relay and applies voltage directly to the left cooling fan through the switch side of the relay, which is fed by the fan 2 fuse. At the same time, the ECM energizes fan 2 relay pulling the switch side over, providing a direct path to ground for the right cooling fan, which has voltage applied through the energized fan 1 relay. In high speed mode, the fans are operated as a parallel circuit with full voltage applied to each.
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
Description and Operation
Cooling Fan Description and Operation
Connector End View Reference
Cooling System Connector End Views
Electrical Information Reference
* Circuit Testing
* Connector Repairs
* Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs
Scan Tool Reference
Scan Tool Data List
Circuit/System Verification
1. Verify that DTCs P0480 or P0481 are not set.
^ If either 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
1. Ignition OFF, disconnect fan 3, fan 1, and fan 2 relays.
2. Connect a 30-amp fused jumper between the normally-open switch contact terminals at the fan 2 relay connector in order to complete the right fan ground circuit. Leave this jumper in place for the remainder of this procedure.
3. One at a time, connect a 30-amp 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.
4. Ignition ON, connect a 30-amp 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.
5. If the circuits and fans test normal, replace the relay.
Repair Instructions
* Engine Coolant Fan Motor Replacement
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)
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.