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 fan 1 relay. Voltage is applied directly to the right 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 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 fan 1 relay, the fan 2 relay, and the fan 3 relay. Voltage is applied directly to the left cooling fan through the switch side of the fan 3 relay. The left cooling fan obtains voltage through the fan 1 relay and ground through the fan 2 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, a DTC will set and the affected ECM driver will be disabled.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling System 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 a DTC is set, repair the DTC first. Refer to DTC P0480, P0481, P0691, P0692, P0693, or P0694.

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.

1. Ignition OFF, disconnect the cooling fan relays.
2. Connect a 30A fused jumper between the relay switch circuit terminal 30 and the ground circuit terminal 87 at the fan 2 relay connector. This will complete the left 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 3 relay circuit and the low speed fan 1 relay circuit.

3. Ignition ON, verify that a test lamp illuminates between ground and the relay switch B+ circuit terminal 30.

⇒

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 relay.

Note:  The following test must be performed first on the high speed fan 3 relay circuit and next on the low speed fan 1 relay circuit. Leave the jumper connected to the low speed fan 1 relay circuit for the next test.

4. Connect a 30A fused jumper between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87. Verify the appropriate fan is activated

⇒	If the appropriate fan does not activate, test the relay controlled output circuit for a short to ground or an open/high resistance. If the circuit tests normal, test the fan ground circuit for an open/high resistance. If the circuit tests normal, replace the fan.

5. Install the fan 3 relay. Verify both fans activate at low speed.

⇒	If both fans do not activate, test the relay controlled output circuit terminal 87A of the fan 2 relay for a short to ground or an open/high resistance.

6. If all circuits test normal, test or replace the appropriate relay.

1. Ignition OFF, disconnect the appropriate cooling fan relay.
2. Test for 70-110 ohms of resistance between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified range, replace the relay.

Note: This test only applies to 5 terminal relays.

4. Test for less than 2 ohms of resistance between terminals 30 and 87A.

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

5. Install a 20A 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 ohms of resistance between terminals 30 and 87.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.