The engine control module (ECM) controls the low speed cooling fan operation by grounding the low speed fan relay control circuit with an internal solid state device called a driver. For high speed cooling fan operation, the ECM grounds the high speed and S/P relay control circuit at the same time the low speed control circuit is grounded. Battery positive voltage is supplied to the low speed, high speed and S/P fan relays. 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 potential of the control circuit should be high, near battery voltage.

DTCs P0693 and P0694 are type B DTCs.

DTCs P0693 and P0694 are type B DTCs.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Scan Tool Reference

Control Module References

Ignition ON, command each relay ON and OFF with a scan tool. Feel or listen to verify that each relay turns ON and OFF with each command.

1. Ignition OFF, disconnect the appropriate fan relay.
2. Ignition ON, verify that a test lamp does not illuminate between the earth terminal and a known ground.

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

3. Ignition ON, Connect a test lamp between the control circuit terminal and a known ground.

Command the 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 is always ON, test the relay control circuit for a short to voltage. If the circuit tests normal replace the ECM.

⇒	If the test lamp is always OFF, test the relay control circuit for a short to ground or an open/high resistance. If the circuit tests normal replace the ECM.

4. Connect a test lamp between the Battery + terminal and a known ground.

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

5. Connect a 30A fusible link wire between the battery positive post and the fan voltage supply circuit terminal and verify fan activation.

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

6. If all circuits test normal replace the affected relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Ignition ON, command the relay ON and OFF with a scan tool. Feel or listen to verify that the relay turns ON and OFF with each command.