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How To Replace the Coolant Temperature Sensor in Your Car


A faulty coolant temperature sensor can cause serious engine issues, including overheating and poor performance. Despite its potential severity, a bad sensor might not trigger a check engine light, so it’s important to recognize the signs and know how to address the problem.

What Does the Coolant Temperature Sensor Do?

The coolant temperature sensor (ECT) monitors engine coolant temperature and sends this data to the engine control module (ECM) or powertrain control module (PCM). This information helps control the cooling fan, air-to-fuel ratio, and spark timing.

Location of the Coolant Temperature Sensor

The sensor’s location varies by vehicle make and model. Typically, it’s near the thermostat housing, often at the top of the engine by the intake manifold and cylinder heads. It can also be found on or near the water pump housing.

Signs of a Bad Coolant Temperature Sensor
  • Engine overheating or running too cool
  • Erratic temperature gauge readings
  • Check engine light or other temperature-related warning lights
  • Constant or never-running electric cooling fan
  • Poor fuel efficiency
  • Rough engine performance

A failing sensor might cause the engine to run rich, leading to fuel smell, black smoke from the exhaust, and rough idling. Testing the sensor with a voltmeter or diagnostic tool can confirm if replacement is needed.

Cost of Replacement

The sensor typically costs $15-$50. Professional installation may add $150-$400 in labor costs, plus the cost of coolant, about $15.

DIY Replacement Steps
  • Cool the engine completely.
  • Locate and clean the sensor area.
  • Drain the radiator coolant if necessary.
  • Disconnect the electrical connection and remove the sensor.
  • Install the new sensor with appropriate sealant and torque.
  • Reconnect the electrical connection, add coolant, and check for leaks.
  • Run the engine to eliminate air pockets in the cooling system.
Common Mistakes
  • Over-tightening the sensor
  • Cross-threading, causing leaks
  • Not applying sealant
  • Using incorrect or low-quality sensors
  • Mixing incompatible coolants
  • Installing dissimilar metals, risking corrosion

Driving with a bad sensor can lead to severe engine damage. If the engine isn’t overheating, short-term driving is possible, but immediate repair is advised.

Replacing the sensor is generally straightforward with basic mechanical skills and tools, depending on its accessibility.
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