Cooling Fan Always On (Dual Fan)

Cooling Fan Always On (Dual Fan)

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 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 one fan at a high speed
- Cooling Fan Relay 1, 2 and 3 operates both fans at a high speed

* KR20 cooling fan relay identification:

- KR20C cooling fan low speed FAN 1 Relay
- KR20D cooling fan high speed FAN 2 Relay
- KR20E cooling fan speed control FAN 3 or S/P Relay

* 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 ([1][2]Cooling System)
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 a DTC is set, refer to DTC P0480 or P0481 (V8 and V6-LF1, LGD - Dual Fan) (Engine Cooling)DTC P0480 or P0481 (V6-LF1) (V6-LF1).

2. Ignition ON, observe the scan tool FC Relay 1 and FC Relay 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.
2. Ignition ON, observe that the cooling fans are not activated.

• If the fans are activated, test for a short to voltage in the relay controlled output circuit.
• If the fans are not activated, test or replace the appropriate KR20 cooling fan 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 OL.

* 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 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 (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))