Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

The powertrain control module (PCM) commands 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 a higher speed.

In low speed operation, the PCM applies ground to the coil side of the COOL/FAN Relay 1. This energizes the coil and applies voltage to the left cooling fan through the switch side of the relay, which is fed by the COOL/FAN fuse. After voltage has passed through the left cooling fan, it continues through the COOL/FAN Relay 3, which acts as a series/parallel relay, controlling fan speed. In low speed, the COOL/FAN Relay 3 passes voltage to the right cooling fan, effectively operating both fans in a series circuit. From the right cooling fan, a ground path is given through G115.

In high speed operation, the PCM applies a ground to the coil side of the COOL/FAN Relay 1, COOL/FAN Relay 2, and COOL/FAN Relay 3. On the COOL/FAN Relay 2, the energized coil closes the switch side of the relay and applies voltage to the right cooling fan. The energized COOL/FAN Relay 3 pulls the switch side over, providing a direct path to ground for the left cooling fan, which has voltage applied through the energized COOL/FAN Relay 1. In high speed mode, the fans are operated as a parallel circuit with full voltage applied to each.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Cooling System Connector End Views

Description and Operation

Cooling System Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, command the Fan Relay 1 output control ON and OFF with a scan tool. Verify both fans low speed function turns ON and OFF with each command.

⇒	If the fan low speed does not turn ON and OFF with each command or only the left cooling fan turns ON and OFF with each command, proceed with the Low Speed Inoperative diagnostic.

⇒	If the fan low speed remains ON at all times when commanding ON and OFF, proceed with the Fans Always ON diagnostic.

2. Command the Fan Relays 1, 2 & 3 output control ON and OFF with a scan tool. Verify the fan high speed function turns ON and OFF with each command.

⇒	If the fan high speed does not turn ON and OFF with each command, proceed with the High Speed Inoperative diagnostic.

⇒	If the fan high speed remains ON at all times when commanding ON and OFF, proceed with the Fans Always ON diagnostic.

Low Speed Inoperative

1. Ignition OFF, disconnect the COOL/FAN Relay 1.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal F3 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit terminal E5 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal E3 for a short to ground. If the circuit tests normal, test or replace the left cooling fan.

4. Verify that a test lamp illuminates between the B+ circuit terminal F5 and ground.

⇒	If the test lamp does not illuminate, test the B+ for a short to ground or an open/high resistance.

5. Connect a test lamp between the B+ circuit terminal E5 and the control circuit terminal F3.
6. Command the Fan Relay 1 output 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 is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the PCM.

7. Connect a 40-amp fused jumper wire between the B+ circuit terminal F5 and the control circuit terminal E3.
8. Disconnect the harness connector at the left cooling fan.
9. Connect a test lamp between the control circuit terminal B and ground. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the COOL/FAN Relay 1.

10. Reconnect the harness connector at the left cooling fan.
11. Disconnect the COOL/FAN Relay 3.
12. Test for B+ between the control circuit terminal B3 and ground.

⇒	If less than B+, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the left cooling fan motor.

13. Reconnect the COOL/FAN Relay 3.
14. Disconnect the harness connector at the right cooling fan.
15. Ignition OFF, test for less than 1.0 ohm of resistance between the right cooling fan ground circuit terminal A and ground.

⇒	If greater than 1.0 ohm, test the ground circuit for an open/high resistance.

16. Ignition ON, test for B+ between the control circuit terminal B and ground.

⇒	If less than B+, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the COOL/FAN Relay 3.

17. If all circuits test normal, test or replace the right cooling fan.

High Speed Inoperative

1. Ignition OFF, disconnect the COOL/FAN Relay 2.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal B6 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify a test lamp illuminates between the B+ circuit terminal B8 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal A6 for a short to ground. If the circuit tests normal, test or replace the COOL/FAN Relay 2.

4. Verify that a test lamp illuminates between the B+ terminal A8 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Connect a test lamp between the B+ circuit terminal B8 and the control circuit terminal B6.
6. Command the Fan Relays 2 & 3 output 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 is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the PCM.

7. Disconnect the COOL/FAN Relay 3.
8. Verify that a test lamp does not illuminate between the control circuit terminal A3 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

9. Verify a test lamp illuminates between the B+ circuit terminal A2 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test or replace the COOL/FAN Relay 3.

10. Connect a test lamp between the B+ circuit terminal A2 and the control circuit terminal A3.
11. Command the Fan Relays 2 & 3 output 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 is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the PCM.

12. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal A1 and ground.

⇒	If greater than 1.0 ohm, test the ground circuit for an open/high resistance.

13. Disconnect the harness connector at the right cooling fan.
14. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal A and ground.

⇒	If greater than 1.0 ohm, test the ground circuit for an open/high resistance.

15. Connect the harness connector at the right cooling fan.
16. Ignition ON, connect a 40-amp fused jumper wire between the B+ circuit terminal A8 and the control circuit terminal A6. Verify the right cooling fan is activated.

⇒	If the right cooling fan does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the right cooling fan.

17. If all circuits test normal, test or replace the COOL/FAN Relay 2.

Fans Always ON

1. Ignition OFF, disconnect the COOL/FAN Relay 2.
2. Ignition ON, verify that a test lamp does not illuminate between the B+ circuit terminal B8 and the control circuit terminal B6.

⇒	If the test lamp illuminates, test the control circuit for a short to ground. If all circuits test normal, replace the PCM.

3. Reconnect the COOL/FAN Relay 2.
4. Disconnect the harness connector at the left cooling fan.
5. Disconnect the COOL/FAN Relay 3.
6. Verify that a test lamp does not illuminate between the B+ circuit terminal A2 and the control circuit terminal A3.

⇒	If the test lamp illuminates, test the control circuit for a short to ground. If all circuits test normal, replace the PCM.

7. Verify that a test lamp does not illuminate between the control circuit terminal A3 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to B+. If the circuit tests normal, replace the COOL/Fan Relay 2.

8. Verify that a test lamp does not illuminate between the control circuit terminal B3 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to B+.

9. Disconnect the COOL/FAN Relay 1.
10. Verify that a test lamp does not illuminate between the B+ circuit terminal E5 and the control circuit terminal F3.

⇒	If the test lamp illuminates, test the control circuit for a short to ground. If all circuits test normal, replace the PCM.

11. Verify a test lamp does not illuminate between the control circuit terminal E3 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to B+.

12. If all circuits test normal, test or replace the COOL/FAN Relay 1.

1. Ignition OFF, disconnect the affected relay.
2. Test for 60-180 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 less than infinite, replace the relay.

4. Install a 20-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2.0 ohms of resistance between terminals 30 and 87.

⇒	If greater than 2.0 ohms, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.