Cooling Fan Always On
Cooling Fan Always On (w/LFA)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (with HP2) (Initial Inspection and Diagnostic Overview)Diagnostic System Check - Vehicle (without HP2) (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) 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.
Reference Information
Schematic Reference
Engine Cooling Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Cooling Fan Description and Operation (Gas w/o LFA) (Description and Operation)Cooling Fan Description and Operation (w/ LFA) (Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Verify that the following DTCs are not set: P0480, P0481, P0482.
• If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions).
2. Verify with a scan tool that the ECM is not commanding fan relay activation.
3. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
4. Ignition ON, observe that the fans are not activated.
Circuit/System Testing
Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description ().
2. Ignition ON, verify the scan tool hood position parameter displays Open.
• If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions) for DTC P254F.
3. Ignition OFF, leave the fan control relay in place while disconnecting the other relays.
4. Ignition ON, observe that the fans are not activated.
• If the fans are not activated, replace the faulty relay.
• If a fan is activated, test the fan voltage supply circuits for a short to voltage.
Repair Instructions
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Underhood Electrical Center or Junction Block Replacement (Underhood Electrical Center or Junction Block Replacement)
Repair Verification
1. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
2. Ignition ON, observe that the fan is not activated.