GM Service Manual Online
For 1990-2009 cars only
Table 1: Cooling Fan 1 Relay
Table 2: Cooling Fan 2 Relay

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 powertrain control module (PCM) controls cooling fan operation in either high speed or low speed mode, depending on cooling requirements. To activate the fan, the PCM applies ground to the coil side of the applicable fan relay. This energizes the coil and pulls the switch side of the relay closed.

In low speed operation, the PCM applies ground to the coil side of the low speed fan 1 relay. This energizes the coil and applies voltage directly to the cooling fan through the switch side of the fan 1 relay. The cooling fan is connected in series to the fan resistor through the de-energized fan 2 relay. The series circuit operates the fan at low speed.

In high speed operation, the PCM applies a ground to the coil side of the low speed fan  relay and the high speed fan 2 relay. When energized, the fan 2 relay a provides a direct path to ground for the cooling fan through the switch side of the relay. Simultaneously, the fan 1 relay continues to provide ignition voltage to cooling fan which enables the fan to operate at high speed.

Diagnostic Aids

    • The fan relay electrical contacts may be pitted or sticking. Replace the relay, if tapping gently on the relay, or wiggling the relay causes a change in the relays operation.
    • The performance of the cooling relay may be affected by temperature. Check the relay after sitting outside overnight and after running the engine 30 minutes.

Use the following relay cavity table in order to locate the correct cavities to probe during diagnosis. The table layout corresponds to the cavity layout of the relay block.

Cooling Fan 1 Relay

Terminal Identification

Relay Controlled Output

Relay Switch B+

Relay Coil Control

Relay Coil Ignition

Front of Vehicle

Cooling Fan 2 Relay

Terminal Identification

Relay Controlled Input

Ground

Relay Coil Control

Relay Controlled Output

Relay Coil Ignition

Front of Vehicle

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Cooling System Connector End Views

Electrical Information Reference

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

DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

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

Circuit/System Verification

  1. Verify the HVAC system operates correctly.
  2. If an HVAC system condition is found, repair the HVAC condition first. Refer to Diagnostic Starting Point - Heating, Ventilation and Air Conditioning.
  3. Ignition ON, observe that the fan is not activated.

Circuit/System Testing

    Important: The following tests must be performed on each cooling fan 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 fan is activated, test for a short to voltage in the relay controlled output circuit.
    If the fan is not activated, test for a short to ground in the relay coil control circuits.
  4. If all circuits test normal, test or replace the cooling fan relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Cooling Fan Relay Replacement