The powertrain control module (PCM) controls cooling fan operation in either high speed or low speed mode, depending on cooling requirements. To activate the fan, the PCM applies ground to the coil side of the applicable fan relay. This energizes the coil and pulls the switch side of the relay closed.

In low speed operation, the PCM applies ground to the coil side of the low speed fan 1 relay. This energizes the coil and applies voltage directly to the cooling fan through the switch side of the fan 1 relay. The cooling fan is connected in series to the fan resistor through the de-energized fan 2 relay. The series circuit operates the fan at low speed.

In high speed operation, the PCM applies a ground to the coil side of the low speed fan  relay and the high speed fan 2 relay. When energized, the fan 2 relay a provides a direct path to ground for the cooling fan through the switch side of the relay. Simultaneously, the fan 1 relay continues to provide ignition voltage to cooling fan which enables the fan to operate at high speed.

Use the following relay cavity table in order to locate the correct cavities to probe during diagnosis. The table layout corresponds to the cavity layout of the relay block.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Cooling System Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Verify the HVAC system operates correctly.

⇒	If an HVAC system condition is found, repair the HVAC condition first. Refer to Diagnostic Starting Point - Heating, Ventilation and Air Conditioning .

2. Ignition ON, command the cooling fan 1 relay ON and OFF with a scan tool. Verify that the fan turns ON and OFF when changing between the commanded states.

1. Ignition OFF, remove the cooling fan relays.

Important:  The following test must be performed on both cooling fan relay circuits.

2. Ignition ON, verify that a test lamp illuminates between the relay coil ignition circuit terminal 1 and ground.

⇒	If the test lamp does not illuminate, test the relay coil ignition circuit for a short to ground or an open/high resistance.

3. Connect a test lamp between the Fan 1 Relay coil control circuit terminal 2 and the relay coil ignition circuit terminal 1.
4. Command the cooling fan 1 relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp does not turn ON and OFF, test the relay coil control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the PCM.

5. Connect a test lamp between the Fan 2 Relay coil control circuit terminal 2 and the relay coil ignition circuit terminal 1. The test lamp should not illuminate.

⇒	If the test lamp illuminates, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the PCM.

Important: An engine coolant temperature (ECT) sensor fault will cause the engine cooling fan to turn ON at high speed.

6. Disconnect the engine coolant temperature (ECT) sensor electrical connector. Verify the test lamp illuminates when the ECT sensor is disconnected.

⇒	If the test lamp does not illuminates, test the relay coil control circuit for an open/high resistance. If the circuit tests normal, replace the PCM.

7. Verify that a test lamp illuminates between the fan 1 relay switch B+ circuit terminal 5 and ground.

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If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the RDI FAN fuse is open, test the relay controlled output circuit terminal 3 for a short to ground. If the circuit tests normal, test or replace the relay.

8. Connect a 30A fused jumper between the Fan 2 Relay switch circuit terminal 3 and the relay switch output circuit terminal 4. This will complete the low speed fan ground circuit.
9. Connect a 30A fused jumper between the Fan 1 Relay switch B+ circuit terminal 5 and the relay controlled output circuit terminal 3. Leave this jumper in place for the remainder of this procedure. Verify the cooling fan turns ON at low speed.

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If the fan is OFF, test the fan 1 relay controlled output circuit terminal 3 and the fan 2 relay controlled output circuit terminal 4, including the fan resistor, for an open/high resistance. If the circuits and resistor test normal, test the cooling fan ground circuit for an open/high resistance. If the circuit tests normal, replace the cooling fan.

10. Connect the 30A fused jumper between the Fan 2 Relay switch circuit terminal 3 and the ground circuit terminal 5. Verify the cooling fan turns ON at high speed.

⇒	If the fan is OFF, test the relay ground circuit terminal 5 for an open/high resistance. If the circuit tests normal, replace the cooling fan.

11. If all circuits test normal, test or replace the cooling fan relay.

1. Ignition OFF, disconnect the relay.
2. Test for 85-120 ohms at 20°C (68°F) between terminals 1 and 2.

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

3. Test for infinite resistance between the following terminals:

•

5 and 1

•

5 and 2

•

5 and 3

•

1 and 3

•

2 and 3

⇒	If not the specified range, replace the relay.

4. Test for less than 2 ohms between terminals 3 and 4.

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

5. Install a 20A fused jumper wire between relay terminal 1 and 12 volts. Install a jumper wire between relay terminal 2 and ground. Test for less than 2 ohms between terminals 3 and 5.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.