Cooling Fan Always On
Cooling Fan Always On
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 the diagnostic category.
Circuit/System Description
The engine cooling fan system is composed of one cooling fan, a series of 5 relays, the engine control module (ECM), and the associated wiring. The cooling fan assembly includes two resistors. This combination of components enables the ECM to operate the cooling fan at 3 speeds using two fan control circuits.
Diagnostic Aids
* The scan tool cooling fan output control operates as follows:
- Cooling Fan Relay 1 operates the fan at a low speed
- Cooling Fan Relay 2 and 3 operates the fan at a medium speed
- Cooling Fan Relay 1, 2 and 3 operates the fan at a high speed
* Certain resistance conditions with IAT or ECT sensors may cause unwarranted cooling fan activation. If the ECM is commanding the cooling fans ON for no apparent reason and without any component or system DTCs set, the IAT or ECT sensor may be skewed. If this condition is suspected, refer to the Temperature Versus Resistance tables in the appropriate engine controls subsection.
* If the cooling fan operates at high speed when the ECM is requesting medium speed operation, test or replace the KR20E Cooling Fan Speed Control Relay.
Reference Information
Schematic Reference
Engine Cooling Schematics [1][2]Cooling System
Connector End View Reference
* Component Connector End Views Sunshade - Left (D61)
* Electrical Center Identification Views X50A Fuse Block - Underhood Label
Description and Operation
Cooling Fan Description and Operation Cooling Fan
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.
2. Verify that there are no cooling system DTCs set.
• If any DTCs are set
Refer to Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle.
• If no DTCs are set
3. Verify the scan tool parameters listed below display OFF.
* Cooling Fan Relay 1 Command
* Cooling Fan Relays 2 and 3 Command
• If a scan tool parameter displays ON
Refer to Diagnostic Aids and Symptoms - Engine Cooling Symptoms - Engine Cooling for further diagnosis.
• If both scan tool parameters display OFF
4. Verify that the fan is not activated.
• If the fan is operating
Refer to Circuit/System Testing.
• If the fan is OFF
5. All OK.
Circuit/System Testing
Note: The following tests must be performed on each cooling fan relay.
1. Ignition OFF, disconnect each KR20 cooling fan relay one at a time, in the order listed below, ignition ON:
* KR20F Cooling Fan Relay
* KR20C Cooling Fan Low Speed Relay
* KR20P Cooling Fan Medium Speed Relay
* KR20D Cooling Fan High Speed Relay
2. Verify that the cooling fan is not activated after each relay is removed.
• If the cooling fan is ON with all of the listed relays removed
1. Ignition OFF, disconnect the harness connector at the G10 Cooling Fan Motor, ignition ON.
2. Test for less than 1 V between ground and the relay controlled output circuit terminal listed below:
* KR20C Cooling Fan Low Speed Relay terminal 87
* KR20P Cooling Fan Medium Speed Relay terminal 5
* KR20D Cooling Fan High Speed Relay terminal 3
• If 1 V or greater, repair the short to voltage in the appropriate circuit.
• If the cooling fan is OFF after a listed relay is removed
3. Replace the appropriate KR20 Cooling Fan Relay.
Component Testing
1. Ignition OFF.
2. Disconnect a KR20 Cooling Fan Relay.
3. Test for 70-110 ohms between terminals 85/2 and 86/1. 95-135 ohms for the KR20F Cooling Fan Relay.
• If less than or greater than the specified range
Replace the KR20 Cooling Fan Relay.
• If within the specified range
4. Test for infinite resistance between the following terminals:
* 30/3 and 86/1
* 30/3 and 87/5
* 30/3 and 85/2
* 85/2 and 87/5
• If less than infinite resistance
Replace the KR20 Cooling Fan Relay.
• If infinite resistance
5. Install a 20 A fused jumper wire between relay terminal 85/2 and 12 V.
6. Install a jumper wire between relay terminal 86/1 and ground.
7. Test for less than 2 ohms between terminals 30/3 and 87/5.
• If 2 ohms or greater
Replace the KR20 Cooling Fan Relay.
• If less than 2 ohms
8. All OK.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)