Coolant Temperature Sensor

What is a coolant temperature sensor and where is it located?

Your engine is pretty hot stuff, but if it gets too hot, you’re going to start to have problems. That’s where your sensors, like the coolant temperature sensor (CTS), come into play. Also sometimes referred to as an engine coolant temperature (ECT) sensor or coolant temperature switch, sensors help keep your engine operating smoothly at the right temperature. Temperature sensors are thermistors, resistors whose resistance changes with temperature. Your vehicle’s computer, the engine control module (ECU), sends a reference voltage to the temperature sensor and can determine what temperature it is experiencing by the difference in its output temperature. 

Your car or truck may have more than one coolant temperature sensor. One is mounted near the thermostat and is in contact with the coolant. It sends information to the ECU about the temperature so that the ECU can make adjustments to how the engine is running. Another sensor, known as the coolant temperature sending unit or sender, sends a signal to the temperature gauge or light on your dashboard to let you know if your engine is running hot. The temperature sending unit may be found near the thermostat. Some engines will have a separate sensor that signals the radiator cooling fan to turn on. Often though, a vehicle will have only one single engine coolant temperature sensor that sends the information to the ECU, which then controls the radiator fan and gauge or light on the dash.

The ECU will make many adjustments based on the information from the engine coolant temperature sensor. It may signal the fuel injectors to add more fuel, allowing the engine to run rich in cold conditions. It may prevent or allow exhaust gas recirculation. It may affect the idle speed. It may affect ignition timing. In engines without a separate temperature sending unit for the cooling fan, the ECU may activate the cooling fan based on information from the automotive temperature sensor.

How do I know if my coolant temperature sensor needs to be replaced?

A faulty coolant temperature sensor will often result in a check engine light and diagnostic trouble code. Common OBD II trouble codes related to coolant temperature sensor issues will range P0115 to P0119, as shown below.

OBDII Check Engine Codes related to Coolant Temperature Sensors

P0115 Engine Coolant Temperature Circuit Malfunction
P0116 Engine Coolant Temperature Circuit Range/Performance Problem
P0117 Engine Coolant Temperature Circuit Low Input
P0118 Engine Coolant Temperature Circuit High Input
P0119 Engine Coolant Temperature Circuit Intermittent
P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control
P0126 Insufficient Coolant Temperature for Stable Operation
P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

The coolant temperature sensor can be corroded over time or cracked or damaged through exposure to high heat. If your engine has overheated you may want to replace your temperature sensor. These problems can often be identified by visual inspection of the ECT sensor. 

Problems with the coolant temperature sending unit can cause faulty readings from the temperature gauge or light. You might find that the gauge reads cold even when the engine has been running. There is a simple test you can run to ensure that the problem is with the ECT sensor and not the gauge. Locate the sending unit and have a helper turn the key to 'run' or 'on' and watch the temperature gauge. When you unplug the wire from the sensor, the gauge should go to its lowest position. Touch the end of the lead to a piece of iron (the engine block or a bracket). When you ground the wire, the temperature gauge should go to its highest reading. If your gauge does not work correctly during normal running but responds as above, then your gauge is fine but your coolant temperature sensor is bad.

If you have a dash light, it should turn on briefly, as a test, at starting and then go off. The engine is cool at starting, so if the light stays on, then it could be receiving a faulty signal from the temperature sending unit.

Can I replace a coolant temperature sensor myself?

Considering how important your coolant temperature switch is, it’s a good thing that replacing a faulty temperature sensor is fairly easy. You may need to drain the coolant before removing the CTS to avoid unwanted leaks. You may need to remove the air intake or other nearby parts in order to access the temperature sensor. Then, it’s just a simple matter of disconnecting the temperature sensor wiring harness and unscrewing the sensor; some applications however may require the need for a specific coolant sensor socket to do so. You can then simply reverse these steps to install the new coolant temp sensor. Depending on the manufacturer of your car or truck, you may need to apply thread sealant to your new automotive engine temperature sensor. 

Need a coolant temperature sensor replacement?

Your vehicle’s engine coolant temperature sensor is very important, thus if it is in need of replacement, it is imperative that you get a new one and have it installed ASAP. Here at 1A Auto, we carry a large selection of aftermarket coolant temperature switches and sending units for many makes and models, and at great prices. Our parts are just what you need to get your vehicle back in tip-top shape once again!

We also make shopping for a replacement engine coolant temp switch for your car, truck, SUV or van easy here at 1A Auto- we're here to help you select the right part for your vehicle! Call our customer service toll free at 888-844-3393 if you have any questions about our aftermarket coolant temperature sensors, warranty, compatibility or to purchase, or you can buy online.