Cooling Fan Always On with V8

One Cooling Fan-3 Relays

The engine cooling fan system consists of one electrical cooling fan, two resistors, and three fan relays. The relays are arranged in a configuration that allows the engine control module (ECM) to operate the fan at low, medium, or high speeds, depending on cooling requirements. These speeds are obtained by three separate circuits within the cooling fan. Each circuit contains a unique resistance value. The cooling fan and fan relays receive battery positive voltage from the underhood fuse block. The ECM controls the 3 relays by grounding the relay control circuit.

Two Cooling Fans-3 Relays

The engine control module (ECM) commands the fans ON in high speed or low speed. In low speed, the fans are configured in series. In high speed, the fans are configured in parallel.

In low speed operation, the ECM applies ground to the coil side of the low speed relay, which is R1 cool/fan 1 relay. Voltage is applied directly to the left cooling fan through the switch side of the low speed relay. The right fan is connected in series to the left fan through the de-energized series/parallel relay, which is R7 cool/fan 2 relay, so that both fans operate at low speed.

In high speed operation, the ECM applies a ground to the coil side of the low speed relay, the series/parallel relay, and the high speed relay, which is relay R2 cool/fan relay. Voltage is applied directly to the right cooling fan through the switch side of the high speed relay. The left cooling fan obtains voltage through the low speed relay and ground through the series/parallel relay.

When the ECM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding a fan relay OFF, the voltage of the control circuit should be high, near battery voltage. If the ECM detects that the actual voltage of the relay control circuit is different than the expected voltage, DTC P0480 or P0481 will set and the affected ECM driver will be disabled.

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Verify that DTCs P0480, P0481, P0691, P0692, P0693 and P0694 are not set.

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

2. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
3. Ignition ON, observe that the fan is not activated.

Important: The following tests must be performed on each relay.

1. Ignition OFF, disconnect each cooling fan relay, one at a time.
2. Ignition ON, observe that the fan is not activated.

⇒	If the fan is activated, test for a short to voltage in the relay controlled output circuit.

⇒	If the fan is not activated, test or replace the appropriate cooling fan relay.

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.

Cooling Fan Always On with V6

The engine cooling fan system consists of one electrical cooling fan, a serviceable resistor module mounted in the cooling fan shroud, and three fan relays. The relays are arranged in a series parallel (S/P) configuration that allows the engine control module (ECM) to operate the fan at low, medium, or high speeds, depending on cooling requirements. The resistor module is a self-contained unit providing a specific resistance through three individual circuits. To activate the fan, the ECM applies ground to the coil side of the applicable fan relays. The cooling fan and fan relays receive battery voltage from the underhood fuse block. The ground path for the operation of the cooling fan is provided at G104.

When disconnecting electrical connectors 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.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Verify that DTC P0480, P0481, P0691, P0692, P0693 or P0694 is not set.

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

2. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
3. Ignition ON, observe that the fan is not activated.

Note: The following tests must be performed on each cooling fan relay.

1. Ignition OFF, disconnect each cooling fan relay one at a time.
2. Ignition ON, observe that the cooling fan is not activated.

⇒	If the fan is activated, test for a short to voltage in the relay controlled output circuits.

⇒	If the fans is not activated, test or replace the appropriate cooling fan relay.

1. Ignition OFF, disconnect the appropriate cooling fan relay.
2. Test for 200-240 Ω between terminals 85 and 86 of the relay.

⇒	If not within the specified range, replace the 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 value, replace the relay.

4. Test for less than 2 Ω between terminals 30 and 87A.

⇒	If greater than the specified range, replace the relay.

5. Install a 20 A fused jumper wire between B+ and relay terminal 85. Connect a jumper wire between relay terminal 86 and ground. Test for less than 2 Ω between terminals 30 and 87.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Relay Replacement