Updated: Jun. 20, 2024
A faulty coolant temperature sensor can damage your engine. Here's how to tell if yours has gone bad, plus how to fix it.
If your car is overheating, smoking or otherwise running rough, it might be because your coolant temperature sensor has gone bad. Even though this can be a serious enough problem to cause engine failure, it won’t always throw a check engine light, so it’s important to know what signs to look out for.
From diagnosis to fixing the problem, here’s what to know about coolant temperature sensor replacement.
On This Page
What Does the Coolant Temperature Sensor Do?
A car’s engine coolant temperature sensor (ECT) monitors the coolant temperature. It then sends that information to the engine control module (ECM) or powertrain control module (PCM) so the computer can control the cooling fan, air-to-fuel ratio and spark timing.
Where Is the Coolant Temperature Sensor Located?
It depends on your vehicle’s make and model, but commonly the coolant temperature sensor is located near the thermostat housing, which is often toward the top of the engine by the intake manifold and cylinder heads. If it’s not there, it could be in a cylinder head integrated into the thermostat housing.
“Alternatively, the coolant temperature sensor can occasionally be found mounted on or very near the water pump housing on the engine as well,” says Paul Knoll, an automotive expert with American Muscle.
How To Tell If the Coolant Temperature Sensor Is Bad
TMB Studio
Signs that your coolant temperature sensor may be bad include:
- The engine overheating or running too cool
- Erratic temperature gauge readings
- An illuminated check engine light or other temperature-related warning light on the dash
- The electric cooling fan constantly running, or never running
- Poor fuel efficiency
- A roughly running engine
If a failing sensor causes the computer to think the engine is running too cold, it might add too much fuel, causing the engine to crank excessively when starting, says Duane “Doc” Watson, a technical trainer at Bosch Mobility Aftermarket. “With the fuel running so rich, you might smell fuel, see black smoke coming out of the tailpipe, or feel the engine running rough or shaking when stopped at a light,” he says.
To confirm if you need a coolant temperature sensor replacement, you can test it using a voltmeter or try Bosch’s VET 100 Circuit Analysis Tool 3920, which plugs into the sensor’s socket and is then paired with a diagnostic scan tool to help validate the wiring connections and accuracy of the sensor.
“You can also use a scan tool to see the temp signal and compare that to a laser temp gun aimed right at the coolant temp sensor,” says Chris “Moose” Pyle, a master certified technician with JustAnswer.
How Much Does It Cost to Replace the Coolant Temperature Sensor?
Again, it depends on your vehicle’s make and model. Most sensors cost between $15 and $50. If you pay a mechanic to install it, labor usually takes 1 to 2.5 hours, which might end up costing between $150 and $400.
“There will also be some coolant lost during the procedure,” says Pyle. “So you may need a gallon of coolant as well which is about $15.”
How To Replace the Coolant Temperature Sensor Yourself
Allow the engine to cool completely to avoid injury.
- Locate the sensor and use compressed air to remove any debris. If other vehicle parts are blocking access to the sensor, you may also have to remove them.
- Drain coolant from the radiator as necessary. “If the coolant is in good health, then save it in a clean container so you can reuse it,” says Pyle.
- Carefully unplug the electrical connection and then remove the sensor. Consult a workshop or service manual for tools needed, such as a socket wrench, open-end wrench, pliers or screwdriver.
- Install the new sensor. If it doesn’t come with sealant already on the threads, apply a thin coat of RTV sealant or add or replace the o-rings. Be sure to only tighten it to the torque specs for your model and engine, as per the owner’s manual recommendations. “Typically, it’ll be somewhere around 15 to 18-inch pounds,” says Watson.
- Reconnect the electrical connector. If you choose, you may use a small amount of di-electric grease on the connector terminals to help keep water off of the pins, which would otherwise result in electrical resistance.
- Add coolant.
- Start the engine and check for coolant leaks around the sensor. Also, run the engine with the coolant camp off for a little while to work out any air pockets in the cooling system, says Pyle. “Use the correct coolant upon refill and make sure it is mixed correctly, especially for cold northern states,” he says.
While you’re at it, Knoll also recommends replacing the thermostat if it’s easily accessible, as those often fail around the same time.
Common Mistakes With Coolant Temperature Sensor Replacement
- Over-torquing/tightening the new sensor, which can damage the threads, the part and the intake manifold. “Coolant temperature sensors are designed with a tapered thread, which means the more you screw them in, the tighter they become on a plastic intake, which is what most manufacturers use today,” says Watson.
- Cross-threading the sensor, which can create coolant leaks.
- Forgetting to apply the sealant to the threads.
- Using the incorrect sensor. “I recommend an OEM part instead of a cheap aftermarket one,” says Pyle. “The OEM part is less likely to be a bad new part or fail prematurely.”
- Using the wrong coolant for your car. “Coolants with different chemical makeups don’t mix well,” says Watson. Again, check the owner’s manual for specifications.
Another common pitfall is installing a dissimilar metal, such as a brass sensor into an aluminum intake manifold, which can create electrolysis and cause corrosion in the engine. “If this happens and you attempt to remove the corroded sensor by breaking it loose, you risk breaking the sensor off inside the manifold, leading to another lengthy, costly repair to remove the stuck threads,” says Watson.
FAQs
Is it okay to drive with a bad coolant temperature 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. “That turns a $50 part into a possible $5,000 repair,” says Pyle.
If the engine is not overheating, it is probably safe to keep driving for a day or two, but try to get it into a shop as soon as possible. “If you’re noticing a harder start, smelling excessive fuel or experiencing your car running rough while at a stoplight, the situation might be less dire,” says Watson. “However, remember your car will be using a great deal more fuel in this state, which over time can damage your catalytic converter.”
Is it hard to replace the coolant temperature sensor?
It depends on where the sensor is located. If it’s easy to get to, “Replacing a coolant temperature sensor is generally considered a relatively straightforward job for someone with basic mechanical skills and the right tools,” says Knoll.
About the Experts
- Chris “Moose” Pyle is a master certified technician with 20-plus years of automotive experience. He specializes in gas and diesel engines, transmissions, steering, suspension, brakes and electrical diagnostics. He has also worked as an expert for JustAnswer.com since 2006.
- Duane “Doc” Watson is a technical trainer at Bosch Mobility Aftermarket. He has more than 45 years of experience in automotive repair, has trained thousands of technicians and earned many industry awards, including Chevrolet Technician of the Year and Buick Service Master of the Year.
- Paul Knoll is a dedicated car and truck enthusiast with a lifelong passion for vehicles and sharing his knowledge with the automotive community. He has worked his way up at AmericanMuscle.com and AmericanTrucks.com for more than a decade, and is currently marketing director.
