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How Many Coolant Sensors Does a Car Have?

Coolant sensors detect variations in the temperature of your engine coolant and transmit this information to the temperature gauge on the instrument cluster and the engine ECU. 

More modern vehicles can have at least two coolant temperature sensors. This is so that the vehicle can complete several functions, such as controlling the electric cooling fans and providing data for the ECU and the temperature gauge in the instrument cluster.

Where Are My Coolant Sensors Located?

Coolant sensors are situated in the cylinder head or next to the thermostat.

Older vehicles typically have a single coolant sensor located near the thermostat.

Other older vehicles may have a coolant sensor located in the radiator’s top hose. This is usually an aftermarket modification to eliminate a faulty engine temperature gauge.

How to Diagnose Which Sensor is Faulty?

To diagnose, first, you need to know the symptom of a failed temperature sensor.

Is your temperature gauge not working correctly? Is your car using a lot more fuel than it usually does, or is it running not quite right?

You will need a digital multimeter set to Ohms to test the temperature gauge. Test the sensor’s resistance by placing the multimeter’s black lead on earth and the red lead onto the pin of the temperature sensor.

Test the values when your engine is cold and record the result, then warm the engine up and check the resistance again. There should be a 200-ohm decrease from the initial reading. 

If you do not have approximately 200 ohms decrease, your temperature sensor is faulty. Alternatively, modern vehicles will illuminate the check engine light. Once connected to a scan tool, the fault code will direct you to which temperature sensor is at fault.

What Happens When a Coolant Sensor Fails? 

The first indicator of a faulty coolant sensor is that the temperature gauge reads either cold or hot even though the engine is hot or cold respectively.

More often than not, the gauge will not move at all on the gauge or will go right up past completely hot. Modern vehicles will illuminate the check engine light. 

You may also notice your vehicle overheating despite the gauge on your dash reading cool or lower than usual. You may have trouble starting your car, have poor idle, and your car may blow black smoke.

Your fuel economy may also be poor. This is due to the engine ECU thinking that the car is still cold, where it requires more fuel to run. If the opposite is occurring, your vehicle will be running lean. Prolonged driving on an engine constantly running lean can lead to piston failure.

Manufacturers’ fault codes can vary, but some common codes that you may find relating to the coolant sensors are:

P0115 – Engine Coolant Temperature (ECT) sensor circuit.

P0116 – Engine Coolant Temperature (ECT) sensor performance.

P0117 – Engine Coolant Temperature (ECT) sensor circuit low voltage.

P0118 – Engine Coolant Temperature (ECT) sensor circuit high voltage.

P0119 – Engine Coolant Temperature circuit intermittent.

P0125 – Engine Coolant Temperature (ECT) insufficient for closed-loop fuel control

P0126 – Insufficient ECT for stable operation.

It is also a good idea to check the connectors and wiring harness if the resistance test is inconclusive. A break in the wire or disconnected temperature sensor will read like the sensor is faulty.

How Long Does a Coolant Sensor Last?

Coolant temperature sensors are quite robust; as such, they don’t fail often. If you have bought your new car, you should not expect your coolant temperature sensor to fail, saying that they can and do fail from time to time.

Coolant temperature failures are more common in older vehicles.

Cost to Replace a Coolant Temperature Sensor

Depending on your vehicle, a coolant temperature sensor can cost anywhere from $30 – $200 plus labor.

Most sensors are easily accessible on the engine and, with the right tools, can be replaced by the DIYer. Don’t forget to get some suitable coolant for your vehicle to top up your engine after replacing the sensor.

Is a Car Safe to Drive with A Bad Coolant Sensor?

I would advise excising caution if you decide to continue driving with a faulty coolant temperature sensor. If your gauge is not working correctly, you will not know if an overheating problem occurs with your engine while driving. 

The worst-case scenario of an overheated engine could require an engine rebuild! Continued use of a modern vehicle with a faulty coolant temperature sensor long-term will result in spark plugs fouling and excess carbon build-up in your engine and exhaust.

Though these may be fairly minor repercussions, your vehicle’s long-term performance and fuel economy will be affected, and replacement spark plugs can be quite costly.

In Summary

  • Modern cars usually have more than one coolant temperature sensor.
  • They are usually positioned on the top hose by the radiator or near the thermostat. So modern cars have them fitted on the cylinder head too. 
  • A bad sensor sign is either the car is running cold and not warming up or overheating. This depends on what faulty reading is being sent to the ECU.
  • Coolant sensors don’t usually fail but are an easy fix that a DIY mechanic should be able to do easily enough.
  • Expect to pay at least $30 for a sensor and an additional $100 for labor at a car shop.

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