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 FAN 1 relay. This energizes the coil and applies voltage to the left cooling fan through the switch side of the FAN 1 relay, which is fed by the FAN 1 fuse. After voltage has passed through the left cooling fan, it continues through the FAN 2 relay, which acts as a series/parallel relay, controlling fan speed. In low speed, the FAN 2 relay 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 G100.

In high speed operation, the PCM applies a ground to the coil side of the FAN 1 relay, FAN 2 relay, and FAN 3 relay. On the FAN 3 relay, the energized coil closes the switch side of the relay and applies voltage to the right cooling fan. The energized FAN 2 relay pulls the switch side over, providing a direct path to ground for the left cooling fan, which has voltage applied through the energized FAN 1 relay. 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

When checking the schematics and there are no pinout numbers for the relays or relay connector end views, the following must be understood:

Due to the amount of diagnostic circuit call-outs within the underhood fuse block and the number of relays involved, confusion may result if the above circuit naming guide is not followed. This vehicle carries no schematic pinout call outs per relay to make the diagnostic naming easier. Understanding is based upon circuit function naming.

1. Ignition ON, command the Fans Low Speed output control ON and OFF with a scan tool. Verify the fan low speed function turns ON and OFF with each command.

⇒	If the fan low speed does not turn 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 High Speed 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 FAN 1 relay.
2. Verify that a test lamp illuminates between the FAN 1 relay coil B+ circuit terminal and ground.

⇒

If the test lamp does not illuminate, test the relay coil 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 relay controlled output circuit terminal for a short to ground or a high resistance. If the circuit tests normal, test or replace the FAN 1 relay.

3. Verify that a test lamp illuminates between the FAN 1 relay switch B+ circuit terminal and ground.

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

4. Connect a test lamp between the FAN 1 relay coil B+ circuit terminal and the Low Speed Cooling Fan Relay Control circuit terminal.
5. Ignition ON, command the Fans Low Speed output control ON with a scan tool. The test lamp should turn illuminate.

⇒	If the test lamp does not illuminate, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the PCM.

6. Ignition OFF, connect the FAN 1 relay.
7. Disconnect the harness connector at the left cooling fan.
8. Connect a test lamp between the left cooling fan motor supply voltage circuit terminal B and ground
9. Ignition ON, command the Fans Low Speed output control ON with a scan tool. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the cooling fan motor supply voltage circuit for an open/high resistance. If the circuit tests normal, test or replace the FAN 1 relay.

10. Ignition OFF, connect the harness connector at the left cooling fan.
11. Disconnect the Fan 2 relay.
12. Ignition ON, verify that a test lamp does not illuminate between the Fan 2 relay coil control circuit and B+.

⇒	If the test lamp illuminates, test the Fan 2 relay coil control circuit for a short to ground. If the circuit tests normal, replace the PCM.

13. Command the Fans Low Speed output control ON with a scan tool. Test for B+ between the relay controlled output circuit and ground.

⇒	If less than the specified value, test the relay controlled output circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the left cooling fan.

14. Ignition OFF, reconnect the Fan 2 relay.
15. Disconnect the harness connector at the right cooling fan.
16. 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 the specified range, test the ground circuit for an open/high resistance.

17. Ignition ON, command the Fans Low Speed output control ON with a scan tool. Test for B+ between the right cooling fan supply voltage circuit terminal B and ground.

⇒	If less than the specified value, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the Fan 2 relay.

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

High Speed Inoperative

1. Ignition OFF, disconnect the FAN 3 relay.
2. Verify a test lamp illuminates between the relay coil B+ circuit terminal and ground.

⇒

If the test lamp does not illuminate, test the relay coil 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 relay controlled output circuit terminal for a short to ground or a high resistance. If the circuit tests normal, test or replace the FAN 3 relay.

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

⇒	If the test lamp does not illuminate, test the FAN 3 relay switch B+ circuit for an open/high resistance.

4. Connect a test lamp between the FAN 3 relay coil B+ circuit terminal and the relay coil control circuit terminal.
5. Ignition ON, command the Fan High Speed output control ON with a scan tool. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the High Speed Cooling Fan Relay Control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the PCM.

6. Disconnect the Fan 2 relay.
7. Verify that a test lamp does not illuminate between the Fan 2 relay coil control circuit and ground.

⇒	If the test lamp illuminates, test the Fan 2 relay coil control circuit for a short to voltage.

8. Verify that a test lamp illuminates between the Fan 2 relay coil B+ circuit terminal and ground.

⇒	If the test lamp does not illuminate, test the Fan 2 relay coil B+ circuit for a short to ground or an open/high resistance.

9. Connect a test lamp between the Fan 2 relay coil B+ circuit terminal and the relay coil control circuit terminal.
10. Command the Fan High Speed output control ON with a scan tool. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the High Speed Cooling Fan Control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the PCM.

11. Ignition OFF, test for less than 1.0 ohm of resistance between the Fan 2 relay ground circuit terminal and ground.

⇒	If greater than the specified range, test the Fan 2 relay ground circuit for an open/high resistance.

12. Disconnect the harness connector at the right cooling fan.
13. 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 the specified range, test the ground circuit for an open/high resistance.

14. Connect the harness connector at the right cooling fan.
15. Ignition ON, connect a 40-amp fused jumper wire between the Fan 3 relay switch B+ circuit terminal and the relay controlled output circuit terminal. Verify the right cooling fan is activated.

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

16. If all circuits test normal, test or replace the Fan 3 relay.

Fans Always ON

1. Ignition OFF, disconnect the Fan 3 relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay coil B+ circuit terminal and the High Speed Cooling Fan Relay Control circuit terminal.

⇒	If the test lamp illuminates, test the High Speed Cooling Fan Relay Control circuit for a short to ground. If the circuit tests normal, replace the PCM.

3. Reconnect the Fan 3 relay.
4. Disconnect the Fan 2 relay.
5. Disconnect the harness connector at the right cooling fan.
6. Verify a test lamp does not illuminate between the supply voltage circuit terminal B and ground.

⇒	If the test lamp illuminates, test the supply voltage circuit for a short to voltage. If the circuit tests normal, test or replace the Fan 3 relay.

7. Disconnect the Fan 1 relay.
8. Verify that a test lamp does not illuminate between the relay coil B+ circuit terminal and the Low Speed Cooling Fan Relay Control circuit terminal.

⇒	If the test lamp illuminates, test the Low Speed Cooling Fan Relay Control circuit for a short to ground. If the circuit tests normal, replace the PCM.

9. Reconnect the Fan 1 relay.
10. Disconnect the harness connector at the left cooling fan.
11. Verify a test lamp does not illuminate between the supply voltage circuit terminal B and ground.

⇒	If the test lamp illuminates, test the supply voltage circuit for a short to voltage. If the circuit tests normal, test or replace the Fan 1 relay.

12. Verify a test lamp does not illuminate between the ground circuit terminal A and ground.

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

13. If all circuits test normal, test or replace the Fan 2 relay.

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.