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 each diagnostic category.
Circuit/System Description
The engine cooling fan system is composed of one cooling fan, a series of 3 relays, the engine control module (ECM), and the associated wiring. The cooling fan motor assembly includes two resistors. This combination of components enables the ECM to operate the cooling fan at 3 speeds using two fan control circuits. The underhood fuse block supplies the cooling fan relays with B+ at the switch side, and ignition voltage at the coil side of the relays through separate fuses. When the cooling fan is commanded ON, the ECM grounds the appropriate relay control circuit, which energizes the relay coil. The magnetic field, created within the relay by the energized relay coil, overcomes the spring tension of the bi-metal switch armature causing the relay switch to close. When the relay switch closes, B+ is supplied to the cooling fan motor through the relay controlled output circuit, causing the cooling fan motor to operate. A dedicated ground is supplied to the cooling fan motor to complete the circuit.
Diagnostic Aids
* The ECM has the capability of providing command to the fan relays even when 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:
- 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. Refer to Temperature Versus Resistance (Engine Coolant Temperature Sensor) Temperature Versus Resistance (Engine Coolant Temperature Sensor) if this condition is suspected.
Reference Information
Schematic Reference
Engine Cooling Schematics [1][2]Cooling System
Connector End View Reference
* Component Connector End Views Outside Rearview Mirror - Driver
* Electrical Center Identification Views X50A Fuse Block - Underhood Label
Description and Operation
Cooling Fan Description and Operation (Single Fan, 3 Speed) Cooling Fan Description and Operation (Single Fan, 3 Speed)
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Wiring Repairs Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Engine Control Module Scan Tool Information (LEA) Scan Tool Testing and Procedures for scan tool information
Circuit/System Verification
1. Verify that DTC P0480, P0481, P0691, P0692, P0693, or P0694 is not set.
• If a DTC is set, refer to DTC P0480, P0481, P0691, P0692, P0693, or P0694 P0480.
2. Ignition ON, observe the scan tool Cooling Fan Relay 1 and Cooling Fan Relays 2 and 3 Command parameters. The parameters should display OFF.
3. Ignition ON, observe that the G10 engine cooling fans are not ON.
Circuit/System Testing
1. Ignition OFF, disconnect the KR20C cooling fan relay.
2. Ignition ON, observe that the cooling fan is not activated.
• If the fan is not activated, test or replace the KR20C cooling fan relay.
3. Ignition OFF, disconnect the KR20P cooling fan relay.
4. Ignition ON, observe that the cooling fan is not activated.
• If the fan is activated after the relays are removed, test for a short to voltage in the appropriate relay controlled output circuit.
5. If the circuits test normal, test or replace the KR20P cooling fan relay.
Component Testing
1. Ignition OFF, disconnect the KR20 cooling fan relay.
2. Test for 70-110 ohms between terminals 85 and 86.
• If not within the specified range, replace the KR20 cooling fan relay.
3. Measure the resistance between the terminals listed below. The DMM should display OL.
* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87
• If less than the specified range, replace the KR20 cooling fan relay.
4. 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 ohms between terminals 30 and 87.
• If greater than the specified range, replace the KR20 cooling fan relay.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)