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Common Symptoms of a Faulty Cooling Fan Control (FC) Relay

By R&D
Published on February 3rd, 2025

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Cooling fans in most vehicles use electronic motors to assist in drawing air through the radiator to maintain engine cooling. Cooling fans need to use an electrically operated switch that can turn them ON and OFF and a Cooling Fan Control (FC) Relay serves as the critical component for this task.

This relay is activated when the vehicle’s temperature approaches an excessive threshold temperature, typically 176 – 194°F (80 – 90°C). If the Cooling FC Relay fails, it cannot control the operation of the cooling fan. This leads to engine temperature being too high or too low, which causes negative impacts on engine performance. This article highlights the common symptoms of a malfunctioning Cooling FC Relay, providing insight into potential problems and their underlying causes.

Common Symptoms of a Faulty Cooling Fan Control (FC) Relay

What Causes Cooling Fan Control (FC) Relay Failures?

Physical Damage: Physical damage from vibrations and collisions, such as cracking of the relay housing, and loose connections, can contribute to Cooling FC Relay failures in vehicles, ultimately leading to relay failure.

Electrical Issues: Electrical problems such as electrical overload, and loose connectors can prevent the Cooling FC Relay from functioning properly. If the cooling fan draws more current than the relay is rated for, it can cause the relay to overheat and fail. This overload can result from a short circuit or a fan motor that is drawing too much power due to age or a mechanical problem.

Age and Wear: Over time, the Cooling FC Relay degrades because of the repeated on and off cycling. This leads to poor performance or complete failure of the relay.

Common Symptoms of a Faulty Cooling Fan Control (FC) Relay

Malfunction Indicator Light (MIL) or Check Engine Light (CEL) Illuminates

If the Cooling FC Relay is malfunctioning, the Onboard Diagnostics Generation 2 (OBD2) system in the vehicle will detect a fault. This triggers the vehicle's OBD2 system to illuminate the MIL and store a corresponding Diagnostic Trouble Code (DTC) in its memory. You can use an Innova Scan Tool to identify which DTC has caused the MIL to illuminate.

Cooling Fan Malfunction

When the Cooling FC Relay fails, it cannot supply power to the cooling fan, or it may cause the cooling fan to operate incorrectly. This prevents the engine from operating at the optimal temperature. As a result, it causes abnormal noises, reduces engine performance, drains the battery, and may even cause engine knocking.

Overheating engine

The Cooling FC Relay is responsible for activating the cooling fan when the engine temperature surpasses the maximum threshold. If it malfunctions, it can lead to engine overheating issues because the cooling system fails to work effectively in reducing the engine temperature to the proper operating temperature.

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Identify a Faulty Cooling Fan Control (FC) Relay with the Innova Scan Tool

The Innova Scan Tool is an invaluable diagnostic device that quickly identifies vehicle system issues. It aids in diagnosing and resolving problems related to the Cooling FC Relay by retrieving and identifying associated DTCs. This tool effectively addresses Cooling FC Relay-related issues, helping you easily pinpoint and resolve problems.