Cooling Fan Inoperative
Cooling Fan Inoperative (without HP2)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The engine cooling fan system consists of 2 electric cooling fans and 3 fan relays. The cooling fan relays are arranged in a series/parallel (S/P) configuration. This allows the engine control module (ECM) to operate both fans together at low or high speeds using 2 fan control circuits. The cooling fans receive positive voltage from the cooling fan relays, which receive battery positive voltage from the underhood fuse block. The cooling fans are supplied a ground at G100 and G101.
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.
* The scan tool cooling fan output control operates as follows:
- Fan Relay 1 operates both fans at a low speed
- Fan Relay 2 and 3 operates one fan at high speed
- Fan Relay 1, 2, and 3 operates both fans at high speed
Reference Information
Schematic Reference
Engine Cooling Schematics (Diagrams)
Description and Operation
Cooling Fan Description and Operation (Gas) (Description and Operation)Cooling Fan Description and Operation (Diesel) ()
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Control Module References)for scan tool information
Circuit/System Verification
1. Ignition ON, observe the DTC information with a scan tool. Verify that DTC P0480 or P0481 is not set.
• If a DTC is set, refer to DTC P0480 or P0481 (without HP2) (Without HP2).
2. Ignition ON, command high and low speed fans ON and OFF with a scan tool. Verify that both fans turn ON and OFF when changing between the commanded states.
Circuit/System Testing
Note: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
1. Ignition OFF, disconnect the cooling fan relays.
2. Connect a 30 A fused jumper between the Fan Control relay switch circuit terminal 30 and the relay ground circuit terminal 87. This will complete the left side fan ground circuit. Leave this jumper in place for the remainder of this procedure.
Note: The following test must be performed on both the high speed fan relay circuit and the low speed fan relay circuit.
3. Ignition ON, verify that a test lamp illuminates between ground and the relay switched ignition circuit terminal listed below:
* Fan Low Relay terminal 30
* Fan High Relay terminal 30
• If the test lamp does not illuminate, test the appropriate relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the appropriate G10 cooling fan.
Note: The following test must be performed first on the high speed fan relay circuit and next on the low speed fan relay circuit. Leave the jumper connected to the low speed fan relay circuit for the next test.
4. Connect a 30 A fused jumper between the cooling fan relay circuit terminals listed below:
* Fan High Relay terminals 87 and 30
* Fan Low Relay terminals 87 and 30
Verify the appropriate fan is activated.
• If the corresponding cooling fan does not activate, test the relay controlled output circuit and the cooling fan ground circuit for an open/high resistance. If the circuits tests normal, test or replace the appropriate G10 cooling fan.
• If the corresponding cooling fan activates, replace the appropriate cooling fan relay.
5. Install the Fan Control Relay. Verify both fans activate at low speed.
• If both fans do not activate, test the Fan Control Relay switched output circuit terminal 87A for a short to ground or an open/high resistance.
6. If all the circuits test normal, test or replace the Fan Control Relay.
Component Testing
1. Ignition OFF, disconnect the cooling fan relay.
2. Test for 70-110 ohm between terminals 85 and 86.
• If not within the specified range, replace the cooling fan relay.
3. Measure the resistance between the terminals listed below:
* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87
The DMM should display OL.
• If less than the specified range, replace the cooling fan relay.
4. Test the Fan Control Relay for less than 2 ohm between terminals 30 and 87A.
• If greater than the specified range, replace the cooling fan relay.
5. Connect a 20 A fused jumper wire between relay terminal 85 and B+. Connect a jumper wire between relay terminal 86 and ground. Test for less than 2 ohm between terminals 30 and 87.
• If greater than the specified range, replace the cooling fan relay.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Engine Coolant Fan Motor Replacement (Non-HP2) (Service and Repair)
* 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)