Can a bad temperature sensor cause a fan not working?

Author: Kayli Wuckert  |  Last update: Friday, August 15, 2025

A signal from the coolant temperature sensor is what triggers the ECU to turn on the radiator fan, and if it's faulty, it can prevent the fan from working at all. Test the fan relay. Since the relay operates as a switch for the fan's power, a defective cooling fan relay won't energize the circuit.

Would the heat temperature sensor cause the fan not working?

You can by pass the sensor, which should cause the fan motor to start working . If the motor runs, then it's the sensor that's faulty. The sensor is just a bi-metal switch, when it gets hot and expands it makes contact and turns on the fan. When it cools down the sensor breaks contact and the fan stops.

Does the temperature sensor control the fan?

The sensor only sends temperature data to the control module. The fan is controlled by the programming in the control module.

What happens if my temperature sensor goes bad?

So a bad coolant temp sensor can cause drivability issues, increased fuel consumption and increased engine wear. It will also likely mean that the coolant temperature gauge (if it has one, many cars now only have idiot lights) doesn't work.

Can a bad coolant temperature sensor cause a fan to stay on?

A failed/faulty coolant temp sensor can cause the fan to stay on as a safety measure. The ECU knows it isn't seeing the temp signal correctly so keeps the fan going for a bit to make sure the engine cools down correctly as a protective measure.

Most Common Symptoms of Bad Engine Coolant Temperature Sensor | Signs of failing ECT sensor

What causes a cooling fan to stay on?

In many modern cars, the engine control unit (ECU) monitors the temperature, and if it detects that the engine is still too hot after shutting down, the fan will stay on until the temperature lowers to a safe level. This is particularly common after driving in hot weather or if you've been sitting in heavy traffic.

What happens if I unplug coolant temperature sensor?

It's not recommended to unplug the coolant temperature sensor unless necessary for diagnostic purposes, as it can adversely affect engine operation and potentially cause damage if left unplugged for an extended period.

What are the symptoms of a bad coolant temperature sensor?

How to Spot a Faulty Coolant Temperature Sensor
  • Irregular reading of the dashboard gauge (should be 88-90°C when the engine is warmed up)
  • Overheating engine (highlighted by dashboard gauge)
  • Check Engine Light alert on dashboard.
  • Rough engine sound while idling.

Is it OK to drive with a bad coolant temp sensor?

Not usually, because it can lead to your engine overheating. If you see a red warning light or your car is overheating, do not continue to drive.

What are the symptoms of a bad air temperature sensor?

This can result in poor engine performance such as rough idle, hesitation, reduced power, or sluggish acceleration. If the IAT sensor provides inaccurate readings, the engine may have difficulty starting, especially in cold weather. It may also cause the engine to stall or die shortly after starting.

Why is my radiator fan not kicking on?

It could be a problem with the fan motor, temperature sensor, fan control relay, or wiring. The Check Engine Light might come on. With modern cars, a DTC will be triggered that illuminates the light on the dash when it exceeds normal operating temperatures. It might be accompanied by a message on the cluster too.

Why is the cooler fan not working?

If your air cooler isn't giving you the cooling you need, chances are the cooling pads are clogged with dust or debris. A quick clean with some mild detergent will have them working again in no time. Also, check if the water tank is full, since low water levels can make a big difference in cooling power.

Can a bad thermostat cause the radiator fan not to work?

Yes, a malfunctioning thermostat can indeed cause the fan not to work properly. The thermostat acts as the control center for your HVAC system, including the fan.

Why is the fan not coming on my thermostat?

If the fan does not operate automatically on a call for cooling, or after turning the thermostat fan switch to the "On" position, this may indicate either a bad blower motor or a bad capacitor (below). A failed blower motor will often be accompanied by a bad odor (like burning plastic or rubber).

Which temperature sensor controls the radiator fan?

The coolant temp sensor is the one the commands the radiator through the ecu . once the coolant temp sensor reads above 185–200 degrees the ecu will signal the radiator fan to engage in the on position until ideal temperature is achieved then will shut off.

Why is my HVAC fan not working?

An outside AC fan not spinning could be caused by power supply issues, a faulty capacitor, a burnt out motor, contactor issues, wiring problems, debris or obstruction, a faulty thermostat or control board, or frozen evaporator coils. Contact your local Carrier dealer to help troubleshoot the issue further.

How do I know if my thermostat or temperature sensor is bad?

Symptoms of bad temperature sensor
  1. Erratic Readings. Sudden jumps or drops in temperature readings. ...
  2. Open Circuit: Display shows a very high or infinite temperature. ...
  3. Short Circuit: Display shows a very low or negative temperature. ...
  4. Drift: ...
  5. Noise or Interference: ...
  6. Physical Damage:

What causes a coolant temperature sensor to fail?

Here are some common factors contributing to sensor malfunction: Wear and Tear: Over time, the sensor may deteriorate due to exposure to extreme temperatures and chemicals in the coolant. Corrosion: Corrosion or sediment buildup can affect the sensor's accuracy, leading to incorrect temperature readings.

How do you tell if you need a new coolant temperature sensor?

Pull on that auto mechanic detective cap: Here's how to spot the telltale signs that this senor isn't working well anymore.
  1. The Check Engine Light Is Triggered and Stays Lit. ...
  2. Fuel Is Being Guzzled at an Unusual Rate. ...
  3. Pros with Auto Mechanic Careers Know to Check the CTS When They See Black Smoke.

What happens if you drive with a bad coolant temperature sensor?

If the coolant temperature sensor malfunctions, it could cause your car engine to get overheated. While sometimes a faulty sensor sends a permanent cold signal to the engine, it can also send a permanent hot signal.

Does a coolant temperature sensor affect AC?

The AC uses that sensor to detect outside air temperature, and if it's reading too cold that could prevent the air conditioning from working. My suggestion would be to replace the ambient air temperature sensor and see if the AC starts working after that is replaced.

Can a bad coolant temperature sensor cause rough idle?

The fault with a coolant sensor can manifest in two ways- A coolant temperature sensor that always reads cold may cause the fuel management system to mix fuel with less oxygen and waste fuel. On the other hand, a sensor that always reads hot can cause problems such as stalling, hick-ups, and rough idling.

What to do after replacing the coolant temperature sensor?

After this is done, it's all a matter of refilling your cooling system with coolant (if you chose to drain it), reconnecting the battery (if you chose to disconnect it), and checking for leaks around the new sensor.

Will a temperature sensor throw a code?

If the 'Check Engine' light suddenly comes on, this could imply a hitch with the coolant temperature sensor. If the computer detects an unsavory development with the sensor's circuit or signal, it may set off the 'Check Engine' light. And the light will not go off until a specialist readily addresses the issue.

Why do cooling fans only work when the temperature sensor is unplugged?

With the temp sensor unplugged the ECU either goes into a fault mode and turns on the fans as a safety OR it falsely detects a temperature above 195F which is the approximate trigger temp to flip on your fans. I would recommend replacing the engine coolant temperature sensor and see if that solves your problem.

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