GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 STS 🢒 Engine 🢒 Engine Cooling 🢒 Cooling Fan Always On

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 low speed fan relay. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the low relay. The left fan is connected in series to the right cooling fan through the de-energized series/parallel (S/P) 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 low speed fan relay, the S/P fan relay, and the high speed fan relay. When energized, the high speed fan relay applies voltage directly to the right cooling fan through the switch side of the relay. Simultaneously, the low speed fan relay and the S/P fan relay provide ignition voltage and a direct path to ground for the left cooling fan. With both fans connected in a parallel circuit, each fan receives full voltage and operates at high speed.

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

    •  Cooling System Connector End Views
    •  Cooling System Component Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification
  1. Verify that DTCs P0480, P0481, P0691, P0692, P0693 and P0694 are not set.
    2. ⇒If any cooling system DTCs are set, repair the DTC first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  2. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
  3. Ignition ON, observe that the fan is not activated.

Circuit/System Testing

    Important: The following tests must be performed on each relay.

  1. Ignition OFF, disconnect each cooling fan relay one at a time.
  2. Ignition ON, observe that the cooling fans are not activated.
    3. ⇒If the fans are activated, test for a short to voltage in the relay controlled output circuit.
    ⇒If the fans are not activated, test or replace the appropriate cooling fan relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Relay Replacement