Your car’s coolant temp sensor, which you may also know as a coolant temp switch, is part of your engine’s management system. This sensor keeps track of the overall temperature of the coolant in your engine. If it thinks the engine should make any changes, it sends a signal that tells the engine to optimize for better performance.

Any issues with your coolant temp sensor can lead to a drop in your vehicle’s performance. We’ll show you how to tell if coolant temp sensor is bad and what tools you might need in order to fix it.

Delphi TS10075

Things You’ll Need

The above list is a representation of some of the common tools you will need in order to replace the coolant sensor on your vehicle should you find that it is faulty. You may already have some similar equipment that can work like the examples you see here. We recommend wearing goggles and gloves during this procedure.

Step 1: How to Tell if Coolant Sensor Is Bad

The first step in the process is diagnosing the problem with your coolant sensor. It can involve one of four primary signs that indicate your car’s coolant temp sensor might be bad.

Part 1: Poor Fuel Economy

One of the top ways you can tell if your coolant temp sensor is bad if your vehicle’s fuel economy. If the coolant sensor is faulty, it can send a bad signal to your car’s engine that causes it to use more fuel than it needs.

Part 2: Black Smoke Appears

If you start to notice black smoke coming from your vehicle’s exhaust system, it could be because the coolant sensor is bad. If the computer thinks the engine is cold, it may mix a fuel mixture that is richer than it needs to be and create black smoke in the process.

Part 3: Your Engine Overheats

The third way you might tell if your coolant sensor is bad is an overheating engine. The sensor might fail in such a way that it sends a permanently hot signal to the computer. Such a signal could cause your engine to overheat or misfire.

Part 4: The Check Engine Light Is Active

If your car detects a problem with the internal circuitry of its coolant temp sensor, it may activate the check engine light to warn you about the issue.

Step 2: Preparing Your Vehicle

If you need to replace the coolant temp sensor, you should set your vehicle on a level patch of ground and make sure it is completely cool before you begin working on it. You can jack up the vehicle’s front end once it is in place.

Step 3: Locating the Sensor

You can consult the service manual for your vehicle if you cannot find the position of the coolant sensor. However, you can find the device on the top driver’s side of the engine on most cars.

Step 4: Remove the Caps

You can now open the hood and remove both the radiator and overflow caps from the engine.

Step 5: Drain the Radiator

There are two ways you can drain your vehicle’s radiator. You can drain it slowly by removing the petcock valve, or you can drain it quickly by removing the drain plug. Choose whatever option you prefer or the one that works best with your coolant pan.

Step 6: Insert the Drain Plug

We include this step here because you need to make sure the drain plug is in place before you add more coolant later.

Step 7: Remove the Harness

Your coolant temp sensor should have its own electronic harness. To remove this harness, you can pry the plastic clip open using a flat head screwdriver.

Step 8: Take Off the Sensor

You can now remove the bad coolant sensor. Check for the correct socket size (it is usually 19 millimeters) and use a drive socket to loosen and then remove the sensor from the engine block.

Step 9: Check For Debris

You should check the hole left by the bad coolant temp sensor for any dirt or debris you can remove.

Step 10: Install the New Sensor

We recommend using your hands and a socket extension to screw the new coolant temp sensor into place. You need to be careful when installing this device. If you tighten the new coolant sensor too much, it could cause problems later.

Step 11: Reattach the Harness

You can use the same electrical harness that you had before on the new sensor. Because it clips to the edges of the sensor, you should be able to snap it back into place.

Step 12: Add More Coolant

We recommend adding a batch of new coolant to your vehicle’s radiator so that it can prime the coolant temp sensor properly. It is also important that you follow any procedures for priming your coolant system if necessary. You can also add new coolant to the overflow reservoir now.

Step 13: Release the Vehicle

You can take your car off the jack stands now.

Step 14: Test the Vehicle

Start your car and allow it to warm the engine. Check for any potential problems such as leaks, the ‘Check Engine’ light, a low coolant light, or black exhaust smoke.

Wrapping Up

You now have a complete guide for how to tell if coolant temp sensor is bad and what you can do to fix it. We would love to hear how these steps worked for you if you tried them out already. Please feel free to leave us a comment below.

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