BAD COOLANT TEMP SENSOR SYMPTOMS: Everything You Need To Know

Bad coolant temp sensor symptoms are a change in the car’s mileage, an illuminating check engine, a cloud of black smoke coming from the exhaust pipe, and warnings of engine overheating.

 

Your vehicle’s engine must stay within a specific temperature range to perform properly. However, if the engine’s temperature got very high, your engine can get overheated and damaged completely.

To do the job, your vehicle pushes a certain fluid called the ‘coolant’ to maintain the engine’s temperature. This coolant can also get very hot and should be monitored continuously. Thanks to the coolant temp sensor. With the car getting older, the coolant temp sensor can get damaged or become faulty. If this happens, you must get your car diagnosed by a trained mechanic and get the problem solved. 

In this article, we will walk you through bad coolant temp sensor symptoms along with a list of frequently asked questions related to the coolant temp sensor. 

 

What is the coolant temp sensor?

 

In any vehicle, the engine has to stay within a specific range of temperature to work properly and avoid overheating. To achieve this goal, a mix of fluids passes through the radiator and then around the engine to maintain its required temperature. 

That been said, any engine has to have the optimum amount of coolant fluid around it, and the temperature has to be monitored continuously to avoid overheating and engine failure. That’s why in every engine, there is a coolant temp sensor to measure the engine’s fluid temperature and make sure it is at the right level. 

Once the coolant temperature sensor measures the temperature, it will send a signal to the on-board control system. This system gives a signal to the computer to keep or alter how the engine is functioning. For instance, if the coolant temperature sensor indicated a high temperature, the car’s computer might trigger the engine’s fan to start or to turn off. 

Bad coolant temp sensor symptoms

 

Similar to any car’s part, the coolant temp sensor can get damaged or go bad for a variety of reasons over time. Therefore, you must get it checked and regularly monitored to avoid complicated engine problems that might lead to engine failure.

Here is a list of common bad coolant temp sensor symptoms:

 

• Low vehicle mileage

 

 

If the coolant temperature sensor has a problem, it will send wrong information to the car’s computer that might cause severe damages. For example, say that the coolant temperature sensor said that the engine is cold, this will cause the vehicle to push more fuel to the engine, so it burns it. As a result, the engine can get overheated very fast, which might damage it completely in a very short period. 

 

• Illuminating check engine light

 

 

The car’s computer uses the check engine light to indicate the internal car’s problems. These problems do not necessarily mean an issue with the coolant temperature sensor. 

To know for sure what is the cause of check engine light illuminating, you need to use a code reader tool. This tool grabs the information from the car’s computer and translates it into a code number. Each code number means a certain problem.

For example, the codes below re related to problems with the coolant temperature:

• P0128: This code means that the coolant temperature is below the thermostat regulating temperature.
• P0115: This code indicates an issue with the engine coolant temperature circuit
• P0116: This code means an issue with the engine coolant temperature circuit range
• P0117: This code means that there is a low input in the engine coolant temperature circuit
• P0118: however, this code means that there is a high input in the engine coolant temperature circuit

 

• There is black smoke coming out of the exhaust pipe

 

 

If the coolant temperature sensor indicates a cold engine, the car’s computer will push more fuel to the combustion system. Having a rich fuel mixture, or a lot of fuel in the combustion system will cause black smoke to come out from the exhaust pipe.

 

• Engine overheating problems

 

 

Not surprising, if the coolant temperature sensor keeps indicating cold engine, the engine will perform continuous combustion operations. As a result, the engine will get to a point where it is very hot without any action from the car’s computer to trigger the fan or any ways to cool down the engine. 

 

• Problems with the car’s idling

 

 

If the car’s computer gets the wrong information about the engine’s temperature, causing problems with the fuel mixture adjustments. If the fuel mixture is not adjusted correctly, the car will start experiencing vibration or shaking.

 

• Engine misfire

 

 

Any small problem with the coolant temperature sensors can result in wrong signals sent to the car’s computer and, therefore, poor engine performance or “engine misfire.”

How can I fix the coolant temp sensor’s problems?

 

You might be thinking that the best solution to any coolant temperature sensor is to replace it. Sometimes fixing the problem doesn’t need replacing the piece itself. Therefore, it is recommended that you make a full diagnosis for the coolant temperature sensor using a first digital multimeter, scan tool, or oscilloscope.

For example, it is well-known that the coolant temperature sensor will not perform properly if it is not fully submerged in coolant. In other words, if the coolant level is low for any reason, the coolant temperature sensor will not work. See? In this case, you can fix the problem by filling the coolant to the appropriate level stated in the vehicle’s owner’s manual. 

Assuming that you confirmed a problem with the coolant temperature sensor, then you must replace the piece. Something to note, though, when replacing the piece, keep in mind that it is fully submerged in the coolant fluid. As a result, to replace the coolant temperature sensor, you need to drain the coolant completely. In this case, the coolant might get contaminated; thus, you might need to get the entire system flushed. 

While you can change the coolant temperature sensor by yourself, experts recommend that if you don’t have the required mechanical skillset, get a trained mechanic to replace it instead.

Frequently asked questions about the engine’s coolant temperature sensor:

 

In this section, we will provide you with an overview of the most frequently asked questions about the coolant temperature sensor. 

 

• How to diagnose the coolant temperature sensor?

 

 

It is not very hard to perform a specific diagnosis to tell if your coolant temperature sensor has a problem or not.

Here is all that you have to do:

• Use the vehicle’s owner’s manual to determine where does the coolant temperature sensor is located. 
• Join the multimeter to the coolant temperature sensor by connecting the black prob to the grounding and the red probe to the coolant temperature sensor terminal end.
• Collect the reading on the multimeter
• Run the car’s engine for a little bit
• Collect the multimeter reading before the engine gets hot
• Continue running the engine until it heats up
• Read the multimeter one more time when the engine is hot
• Calculate the difference between the multimeter two readings; when the engine is cold, and when the engine is hot
• Check if the difference is greater than 200 ohms, if that’s the case, this is a sure indication that your coolant temperature sensor has a problem and needs replacement.

 

• How to make the coolant temperature sensor last longer?

 

 

Automotive experts came up with a list of best practices to keep the coolant temperature sensor in good condition for a longer time, including:

• You have to use a specific coolant to fill up the radiator. If tap water was used instead of the special coolant, the elements in this water can cause major problems to the radiator and, therefore, the coolant temperature sensor in the long run. 

 

• Ensure that there is no leak from the oil to the engine’s block. If oil gets mixed with the coolant fluid, it is considered as contamination and can cause significant issues with the coolant temperature sensor. 

 

• Like any other car’s fluid, the coolant liquid has to be in a certain amount to perform properly. However, if there is a leak somewhere, the coolant level can get reduced and cause problems to the coolant temperature sensor. Therefore, it is highly recommended that you keep an eye on the coolant level in your car’s engine. 

 

 

• How much does it cost to replace a coolant temperature sensor?

 

 

Like any other mechanical repair, replacing a coolant temperature sensor requires a cost for the part and the labor. Labor cost depends on the number of hours mechanics spend fixing your issue and the hourly rate for these mechanics. 

For the part itself and depending on the car’s type, expect to pay between $123 and $167 for a coolant temperature sensor replacement cost.

For labor cost, expect to pay between $82 and $105 depending on the location where you will get the job done. 

 

• Where can I find the coolant temperature sensor?

 

 

The location of the coolant temperature sensor differs by car’s make, model, and year. In general, you can find it very close to the cooling system thermostat if not inside it. 

Note that some vehicles have two coolant temperature sensors:

• Coolant temperature sensor: the first sensor sends signals from the engine to the control unit
• Coolant temperature sending unit: the second sensor sends signals to the dashboard. 

 

• How to replace the coolant temp sensor yourself DIY?

 

 

While we mentioned that it is best to get a trained mechanic to replace your coolant temperature sensor, if you feel that you are comfortable of replacing it yourself, here is how to do it:

• Prepare the required tools and safety protective items
• Bring the vehicle’s service manual so you can refer to while doing the job
• Choose the working place that works best for this job. In this case, you must have the car parked on a flat surface like your garage, for example. 
• Use the vehicle’s service manual to identify the location of the coolant temp sensor
• Lift the car’s front using a jack to see best what you are doing
• Take the radiator’s cap off
• Take the overflow cap off
• Open the main drain to drain out all the fluid in the radiator
• Close the main drain after draining it
• Locate electrical connectors in the temperature sensor
• Unplug all electrical connectors
• Take the coolant temperature sensor out form its place
• Clear up any things stuck in the hole where the coolant temp sensor was placed
• Confirm that the new coolant temp sensor matches the old one
• Install the new coolant temp sensor in the right position
• Plug the electrical connectors the way they were connected
• Ensure that the radiator drain plug and the main drain are closed securely
• Fill the radiator with the required amount of coolant as stated in the vehicle’s service manual
• Bring the vehicle down by removing the jack
• Warm the engine up
• Ensure that the coolant is not leaking under the vehicle
• Confirm that there is no check engine light illuminating
• Ensure that there is no indication of low coolant level on the vehicle’s dashboard
• Test the car by driving it
• Recheck the coolant level after one hour of driving the car and ensure that there is no drop in the coolant level. 
• Make sure that you no longer see or notice any of the bad coolant temp sensor symptoms.

Conclusion

 

Your car’s engine has to stay within a specific range of temperatures. Otherwise, it gets overheated and probably damaged. 

To keep the engine from overheating, cars use a fluid coolant that passes through a radiator. This coolant runs around the engine to keep it cold. The coolant’s temperature has to be monitored continuously to ensure that it can cool the engine down. Thanks to the coolant temp sensor. 

Problems with the coolant temp sensor result in significant engine problems that can end up with complete engine failure. Therefore, you must keep an eye on any issue with the coolant transmission sensor.

Specific signs are indicating bad coolant temp sensor like a change in the car’s mileage, an illuminating check engine, a cloud of black smoke coming from the exhaust pipe, and warnings of engine overheating.

If you noticed any of the symptoms mentioned above, you must take your vehicle to an expert mechanic. Don’t change the coolant temperature sensor right away as the problem can be much simpler than that. If you ensured that the issue is really with the coolant temperature sensor, then you must get it replaced as soon as possible.

In the end, never ignore problems related to the coolant temp sensor to avoid very high repair costs from severe damages.