Cooling Fan Comes on When Car Is Cold (Causes & Fixes)

Hasan Amjad
Cooling Fan Turns ON When the Car is Cold

Car engines generate a lot of heat due to combustion, so a cooling system is in place to keep the engine running at an optimal temperature. However, when your cooling fan comes on, even when the car is cold, it’s a sign that something is not quite right.

The cooling fan can activate for various reasons that may not necessarily be positive. Potential issues include a malfunctioning fan relay, a non-functioning ECU, and inaccurate temperature sensor readings, causing the fan to operate continuously despite temperature changes.

This information might seem limited, but there’s no need to worry. In the rest of the article, we will delve into multiple potential causes and help you diagnose and address the problem.

car dashboard

Cooling Fan Turns ON When the Car is Cold [6 Causes and Fixes]

The cooling fan circulates the air around the radiator keeping the engine fluid levels within an optimal temperature range (195°F to 220°F). Usually, the fan only turns on when the engine is hot.

When it turns on when the engine is cold, it indicates some underlying issues that must be addressed immediately. Here are a few potential causes and fixes to help you deal with this common problem:

1. Bad Fan Relay

A fan relay controls the power supply to the cooling fan. It acts as a switch, activating the fan when the engine temperature reaches a certain point and deactivating it once the temperature drops back down.

Over time, when it turns bad due to exposure to extreme temperatures, it can cause the cooling fan to run continuously as it fails to terminate the power supply even during cold temperatures.

How to fix a bad relay?

A bad relay only has one fix, a replacement. Here are the steps to do that:

  1. Find the relay within your vehicle’s fuse box or relay panel by consulting the wiring diagrams in the owner’s manual.
  2. Make sure you disconnect the battery.
  3. Carefully remove the existing relay.
  4. Install a new relay, ensuring all the pins are securely positioned in their respective slots.

2. Stuck Thermostat

The thermostat is a valve that regulates the coolant flow through the engine. When the engine is cold, the thermostat remains closed, which allows the coolant to heat up faster.

Once the engine reaches a predetermined temperature, the thermostat opens, letting the coolant circulate and maintain a consistent operating temperature.

A stuck thermostat may cause the cooling fan to come on when the car is cold because the engine temperature is not accurately regulated.

How to fix a stuck thermostat?

  1. Locate it in your vehicle (usually near the water pump or the upper radiator hose).
  2. Drain the coolant and remove the thermostat housing.
  3. Inspect the thermostat for damage or corrosion and replace it if necessary.
  4. Refill the coolant and test the system to ensure proper operation.
Car interior on display
Photo by Oleksandr Pidvalnyi on

3. Malfunctioning Temperature Sensor

The coolant temperature sensor, or the engine temperature sensor, keeps track of the engine’s temperature and sends this information to the ECU. Based on the temperature readings, the ECU adjusts the cooling fan operation.

A malfunctioning temperature sensor will cause the cooling fan to come on when the car is cold due to inaccurate readings.

How to fix it?

  1. Find the sensor on your vehicle. Usually, it is near the thermostat housing or in the cylinder head.
  2. You can either use the sensor using a multimeter or scan ECU with OBII to get a faulty error code (P0118).
  3. Please take out the sensor and replace it with a fresh one.

4. Problems with ECU/ECM

Cars have either an engine control unit (ECU) or engine control module (ECM) that controls various aspects of your vehicle’s engine, including the cooling system.

It uses input from the temperature sensors to adjust the cooling fan’s operation, keeping the engine at the optimal temperature.

Software glitches or hardware failure can cause the ECU to malfunction. When that happens, it behaves erratically, and it can cause the cooling fan to come on when the car is cold. You may also witness other signs, such as warning lights on the dashboard.  

How to Fix a Bad ECU?

Resolving problems with the ECU/ECM can be more complex than other issues. So, an electrician or company dealerships are usually recommended when addressing software issues.

They scan your vehicle for diagnostic trouble codes (DTCs) using an OBD-II scanner. This helps them identify if there is a specific issue with the ECU/ECM. In some cases, simply clearing the DTCs may resolve the problem.

They will update the ECU software or replace the unit if the issue persists.

5. Faulty Cooling Fan Motor

The cooling fan motor powers the fan blades, which draw air through the radiator to dissipate heat from the coolant. The ECM controls the motor based on the engine’s temperature.

A faulty cooling fan motor may cause the cooling fan to come on when the car is cold due to internal electrical problems. When that happens, the fan behavior is absurd. It may turn on and off on its own and produce a different noise.

How to Fix the Cooling Fan Motor?

  1. Make sure the engine is cold. Then, remove the battery terminals.
  2. Disconnect the electrical connector and take out the cooling fan assembly.
  3. Test the motor using a multimeter, battery, and jumper wires, checking for proper operation.
  4. If the motor is faulty, replace it with a new one and reassemble the cooling fan assembly.

6. Damaged Wiring or Connectors

Wiring and connectors ensure proper electrical communication between the various components of the cooling system, such as the temperature sensors, fan relay, and ECM.

Damaged wiring or connectors can cause the cooling fan to come on when the car is cold due to electrical shorts or intermittent connections.

How to fix it?

First, check the cooling system’s electrical connections to fix damaged wiring or connectors for signs of wear, corrosion, or damage.

Suppose you find any issues, repair or replace the affected wiring or connectors. After the repairs are done, test the system to ensure proper operation.

Frequently Asked Questions

Finally, we have some FAQs related car’s cooling system.

What is the normal operating temperature for a car engine?

The normal operating temperature for a car engine is within the range of 195°F to 220°F (90°C to 104°C). The engines are designed to run optimally within this temperature range, allowing for efficient combustion, reduced emissions, and minimal wear on the engine components.

At what temperature the cooling fan turns on?

This setting may vary based on the make and variant of your vehicle. However, the fan is generally activated when the engine coolant temperature reaches around 200°F.

Final Words

The activation of the cooling fan when the engine is cold suggests the presence of one or more wiring issues within the vehicle. Potential culprits include a faulty fan relay, a malfunctioning ECU, or a bad thermostat.

We trust that our key insights will assist you in pinpointing the cause and addressing the problem accordingly. You can also check out tutorials to see how these repairs can be performed effectively visually.

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