GM Service Manual Online
For 1990-2009 cars only

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.

DTC Descriptor

DTC P0495: Cooling Fan Speed High

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Cooling Fan Relay Ground

--

P0483

--

--

Cooling Fan Relay Voltage Supply

P0480, P0483, P0493

P0480, P0483

--

--

Cooling Fan Relay Control

P0480

P0480

--

--

Hall Effect Sensor Low Reference

--

P0483, P0526

--

--

Hall Effect Sensor 5-Volt Reference

P0642

P0526

P0401, P0643

--

Hall Effect Sensor Cooling Fan Speed Signal

P0526

P0526

P0526

--

Cooling Fan Clutch Fluid Solenoid Valve Ground

--

P0483

--

--

Cooling Fan Clutch Control

P0483

P0483

P0483, P0495

--

Circuit/System Description

The cooling fan relay sends a pulse width modulation (PWM) signal of 12-14 volts to the cooling fan by the cooling fan clutch supply voltage circuit. The control module uses the PWM signal, which controls the speed of the cooling fan clutch by controlling the position of the oil control valve inside the clutch. If the cooling fan clutch RPM is to high when the control module is commanding 0 percent, DTC P0495 will set.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

Cooling fan RPM exceeds 1,700 RPM for 90 seconds.

Action Taken When the DTC Sets

DTC P0495 is a Type C DTC.

Conditions for Clearing the DTC

DTC P0495 is a Type C DTC.

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

    •  Cooling System Connector End Views
    •  Engine Control Module Connector End Views for the 6.6L (LMM) engine

Electrical Information Reference

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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

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

Circuit/System Verification

Engine OFF, verify the fan clutch is not binding by turning the fan by hand.

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the fan shroud.
  2. Operate the engine at 1,500 RPM for 2 minutes. The fan should be quiet to indicate the clutch is disengaged.
  3. If disengaged, test or replace the relay.
    If not disengaged, test the cooling fan clutch supply voltage circuit for a short to voltage. If the circuit tests normal, replace the clutch.

Component Testing

Relay Test

  1. Connect the relay ground terminal to ground and the voltage supply terminal to appropriately fused power to energize the relay.
  2. Test for less than 1 volt between the load voltage supply terminal and ground.
  3. Connect the relay control circuit terminal to ground.
  4. Test for B+ between the load voltage supply terminal and ground.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Fan Clutch Replacement
    •  Control Module References for replacement, setup, and programming