Your car’s coolant temperature sensor quietly keeps everything in balance. It measures the temperature of the engine’s coolant and sends that information to the computer that controls fuel and air flow. When the sensor stops working correctly, the engine can overheat, stall, or burn more fuel than it should.
What the Coolant Temperature Sensor Does
The sensor’s job is simple but important. It tells the engine control unit how hot or cold the engine is. The computer uses that signal to adjust the fuel mixture and ignition timing so the engine runs smoothly at any temperature. If the sensor gives bad data, the computer makes bad decisions—and performance suffers.
Common Symptoms of a Faulty Sensor
When a coolant temperature sensor starts to fail, you’ll notice changes in how the car runs.
- The car idles roughly or smells like unburned fuel
- The temperature gauge acts strangely or stays cold
- The engine overheats without warning
- Fuel economy drops
- The check engine light comes on
If several of these symptoms show up together, the sensor may be sending false signals.
What Causes Sensor Failure
A coolant temperature sensor lives in a tough spot—it faces heat, coolant, and vibration every time you drive. Over time, that takes a toll.
- Corrosion or dirt on the sensor tip
- Cracked housing from temperature swings
- Damaged wiring or loose connections
- Old or contaminated coolant that eats away at metal parts
Any of these issues can make the sensor misread the engine’s temperature.
How to Test the Coolant Temperature Sensor
Testing isn’t complicated, but it takes care and the right tools.
- Let the engine cool completely.
- Find the sensor—usually near the thermostat or radiator outlet.
- Disconnect the plug and look for corrosion or bent pins.
- Use a digital multimeter to check the sensor’s resistance. Compare it to the specs in your car’s manual.
- Reconnect everything, start the engine, and check that resistance changes as the engine warms up.
If readings don’t match the chart or jump around suddenly, the sensor is failing.
Resetting or Replacing the Sensor
Sometimes people try to “reset” the sensor by disconnecting the battery or clearing codes with a scan tool. That might turn off the warning light, but it doesn’t fix the problem if the sensor is bad.
When it’s time to replace:
- Drain some coolant so it sits below the sensor opening.
- Unplug the connector.
- Remove the old sensor and install the new one with a washer or sealant if required.
- Refill the coolant and bleed out air bubbles.
- Clear any codes and test-drive the car.
A trained technician can handle the whole job in about an hour.
Troubleshooting and Cost
Replacing a coolant temperature sensor usually costs between $150 and $300, depending on the vehicle. That includes both parts and labor. A mobile mechanic can often do the repair right at your home or office, saving time and avoiding a tow.
Can You Keep Driving with a Bad Sensor?
You might get away with short trips, but it’s not worth the risk. A faulty sensor can stop the cooling fan from running or make the engine run too rich, which can damage parts over time. It’s best to fix the issue as soon as possible.
When to Call a Professional
If you’ve tested the sensor and still aren’t sure what’s wrong, call in a professional. AutoNation Mobile Service has ASE-certified technicians who can diagnose and replace a coolant temperature sensor on-site. They’ll confirm the repair and make sure your cooling system works as it should.
FAQ
What are the symptoms of a faulty coolant temperature sensor?
Erratic temperature readings, poor fuel mileage, overheating, and rough idle are common signs.
How do I test a coolant temperature sensor?
Use a multimeter to measure resistance at different temperatures and compare it with the manufacturer’s chart.
What causes a coolant temperature sensor to fail?
Heat, corrosion, and wiring damage are the most common reasons.
Can I reset a coolant temperature sensor?
You can clear codes, but a bad sensor will still send false data until it’s replaced.
Is it safe to drive with a bad sensor?
Only for a short distance. Prolonged driving can lead to overheating and costly repairs.
A working coolant temperature sensor helps your engine stay efficient and cool under pressure. If your readings don’t make sense or your check engine light stays on, book a mobile diagnostic visit and keep your car running at the right temperature.
Can’t make it to a repair shop?
No problem — an AutoNation Mobile Service technician will replace the coolant temperature sensor from your driveway. We offer easy online booking and back every repair with a 12-month, 12,000-mile warranty.
Contact us before your sensor turns up the heat and your wallet feels the burn!