Cooling Fan Inoperative
Cooling Fan Inoperative
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 consists of a cooling fan assembly containing two electric cooling fans. The engine control module (ECM) uses two fan control circuits and a series of three relays to command 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.
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 both fans at a low speed
- Cooling Fan Relay 2 and 3 operates the left fan at a high speed
- Cooling Fan Relay 1, 2 and 3 operates both fans at a high speed
* KR20 cooling fan relay identification:
- The KR20C cooling fan low speed relay is COOL FAN LOW Relay K613
- The KR20E cooling fan speed control relay is COOL FAN CNTRL Relay K614
- The KR20D cooling fan high speed relay is COOL FAN HI Relay K612
* When disconnecting or removing fuses and relays from a fuse block, always inspect the component electrical terminals for corrosion and the correct orientation in the fuse block. Test the mating electrical terminals for tightness.
Reference Information
Schematic Reference
Engine Cooling Schematics (Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
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 (Programming and Relearning) 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 or P0481 (P0480) or DTC P0480, P0481, P0691, P0692, P0693, or P0694 (P0480).
2. Ignition ON, command the appropriate fan relay ON and OFF with a scan tool. Verify that the fans turn ON and OFF when changing between the commanded states.
Circuit/System Testing
1. Ignition OFF, disconnect the cooling fan relays.
2. Connect a 30 A fused jumper between the KR20E relay K614 switch circuit terminal 30 and the ground circuit terminal 87. This completes the right 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:
* KR20C Relay K613, terminal 87
* KR20D Relay K612, terminal 87
• 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 KR20 cooling fan relay circuit terminals listed below. Verify the appropriate fan is activated.
* KR20D Relay K612, terminals 87 and 30
* KR20C Relay K613, terminals 87 and 30
• 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, replace the appropriate G10 cooling fan.
• If the corresponding cooling fan activates, replace the appropriate KR20 cooling fan relay.
5. Install the KR20E relay K614. Verify both fans activate at low speed.
• If both fans do not activate, test the KR20E relay controlled output circuit terminal 87A, for a short to ground or an open/high resistance.
6. If all circuits test normal, test or replace the KR20E cooling fan speed control relay.
Component Testing
1. Ignition OFF, disconnect the KR20 cooling fan relay.
2. Test for 70-110 ohm 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 O.L.
* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87
• If not the specified range, replace the KR20 cooling fan relay.
4. Test the KR20E relay for less than 2 ohm between terminals 30 and 87A.
• If greater than the specified range, replace the KR20E cooling fan relay.
5. Install a 20 A fused jumper wire between relay terminal 85 and 12 volts. Install 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 KR20 cooling fan relay.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Relay Replacement (Removal and Replacement)
* Engine Coolant Fan Motor Replacement (Service and Repair)