How To Replace the Coolant Temperature Sensor in Your Car | Family Handyman

By Karuna Eberl

Updated on Aug. 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.

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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.

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.

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Signs that your coolant temperature sensor may be bad include:

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.

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.”

Allow the engine to cool completely to avoid injury.

While you’re at it, Knoll also recommends replacing the thermostat if it’s easily accessible, as those often fail around the same time.

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.

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.”

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.