Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit/System Description
The engine control module (ECM) 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 full speed.
In low speed operation, the ECM applies ground to the coil side of the auxiliary fan relay. This energizes the coil and applies voltage directly to the auxiliary cooling fan through the switch side of the relay. The auxiliary fan is connected in series to the main cooling fan through the de-energized series/parallel control fan relay. The series circuit operates both fans at low speed.
In high speed operation, the ECM applies a ground to the coil side of the auxiliary fan relay, the control fan relay, and the main fan relay. When energized, the main fan relay applies voltage directly to the main cooling fan through the switch side of the relay. Simultaneously, the auxiliary fan relay and the control fan relay provide ignition voltage and a direct path to ground for the auxiliary cooling fan. With both fans connected in a parallel circuit, each fan receives full voltage and operates at high speed.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Cooling Fan Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON, observe the DTC Information with a scn tool. Verify there are no DTCs set.
- Verify with a scan tool that the ECM is not commanding the fans ON.
- Ignition ON, observe that the fans are not activated.
| ⇒ | If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle . |
Circuit/System Testing
- Ignition OFF, disconnect each cooling fan relay one at a time.
- Ignition ON, observe that the cooling fans are not activated.
- If all circuits test normal, test or replace the cooling fan relay.
Important: The following tests must be performed on each cooling fan relay.
| ⇒ | If the fans are activated, test for a short to voltage in the relay switch controlled output circuit. |
| ⇒ | If the fans are not activated, test for a short to ground in the relay coil control circuit. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
