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

* 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.
* 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)
* Electrical Center Identification Views (Application and ID)

Connector End View Reference

Component Connector End Views (Connector End Views By Name)
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. Ignition ON, observe the DTC information with a scan tool. Verify that DTC P0480 or P0481 is not set.

• If any cooling system DTCs are set, repair the DTC first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle).

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 fan is not activated.

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.

* KR20F cooling fan relay
* KR20B cooling fan low speed relay
* KR20A cooling fan medium speed relay
* KR20D cooling fan high speed relay

2. Ignition ON, observe that the fan is not activated after each relay is removed.

• If the fan is not activated, replace the appropriate KR20 relay.
• If the fan is activated, test the appropriate relay controlled output circuit for a short to voltage.

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 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 ohm between terminals 30 and 87.

• If greater than the specified range, replace the KR20 cooling fan relay.

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.