(ECT) Engine Coolant Temperature Sensor – What Can Go Wrong

(ECT) Engine Coolant Temperature Sensor - What Can Go Wrong
(ECT) Engine Coolant Temperature Sensor - What Can Go Wrong

The (ECT) sensor, is an engine management system sensor, that is used to monitor, the temperature of the engine’s coolant.

The tip of the (ECT) sensor, protrudes into one of the cooling system passages and is immersed in coolant.

Most (ECT) sensors operate using electrical resistance, to measure the temperature of the coolant.

A typical (ECT) sensor is a Negative Temperature Coefficient (NTC) thermistor. Because, its electrical resistance, decreases when the temperature increases.

The engines computer receives this signal. So, changes can be made to the engine’s timing and fuel calculations, for optimal performance. Consequently, engines need more fuel, when they are cold and less fuel, when they are warmed up.

The computer will also scale back engine performance settings, if it detects that the engine temperature is too high.

So, it can protect the engine from possible damage, due to overheating. Engine temperature plays, such a vital role in engine performance calculations. Therefore, any problem with the coolant temperature sensor, can quickly translate into an engine performance issues.

How Does It Work

An (ECT) sensor is connected to, the main computer (powertrain control module or (PCM). The (PCM) supplies a reference voltage (typically 5 Volt) and constantly monitors the (ECT) sensor signal. Based on this signal, the (PCM) adjusts the engines performance. It also operates the electric radiator fans, when the temperature reaches, a predetermined level.

(ECT) Sensor With O-Ring Type Of Mounting
(ECT) Sensor With O-Ring Type Of Mounting

If the signal from the sensor is missing, or it is outside of the expected range, the (PCM) turns on the Check Engine light and, stores the related trouble code in its memory.

What Can Go Wrong

One of the common problems is, when the sensor has a, poor connection inside or in the connector. This causes interruptions in the signal to the (PCM) and the (PCM) sets the fault. In some vehicles, symptoms of this problem show up as, erratic readings of the temperature gauge.

The engine may run in fail-safe mode:

  • Air conditioner may stop working
  • Radiator fans may run constantly

Consequently, many check engine light codes, referring to the (ECT) sensor, could also be caused by other reasons. Such as a bad thermostat or issues with the cooling system, including even a leaking head gasket. Therefore, the problem must be properly diagnosed.

So, the tip of the sensor, has to be immersed in coolant. Consequently, a low coolant level inside the cooling system, can cause the signal from the sensor to be incorrect.

Always check the coolant level first. Next, the (ECT) sensor connector, must be checked for damaged pins or corrosion. There are several ways to test the (ECT) sensor, you can find the correct way in the service manual.

Testing Coolant Temperature Sensor (ECT)
Testing Coolant Temperature Sensor (ECT)

Engine efficiency, power and fuel economy all improve, as the engine temperature rises. Ideally, the engine will run as hot as possible, without boiling its coolant or damaging its components. But, a faulty engine coolant temperature (ECT) sensor can, cause havoc on an engine or its related systems.

Common Failure Symptoms

Usually a problem with the (ECT) sensor will show a few failure symptoms:

  • Poor Fuel Economy
  • Black Smoke From Exhaust
  • Engine Overheating
  • Illuminated Check Engine Light
  • Poor Engine Performance Or Stalling
  • Increased Emissions

Poor Fuel Economy

One of the first symptoms, associated with a problem with the (ECT) sensor is poor fuel economy. A failed (ECT) sensor can send a false signal to the computer and throw off the fuel and timing calculations. It is not uncommon for the coolant temperature sensor to fail and send a permanently cold signal to the computer.

This will cause the computer to think the engine is cold, even when it is not. Once the engine is warm, it switches to relying on the oxygen (O2) sensors for a more precise reading. A failed (ECT) sensor can prevent this change from happening, resulting in a rich-running engine and poor fuel economy.

Black Smoke From Exhaust

Another symptom of a possible problem with the (ECT) sensor is, black smoke from the vehicle’s exhaust. A failed sensor can also send, a cold signal to the computer.

Black Tailpipe Smoke
Black Tailpipe Smoke

Consequently, confusing the computer and causing it to, unnecessarily enrich the fuel mixture. If the fuel mixture becomes excessively rich, the fuel cannot be adequately burned. As a result, it will burn up in the exhaust pipes and cause black smoke.

Engine Overheating

Another symptom of a problem with the coolant temperature sensor is, an overheating engine. The coolant temperature sensor can also fail in a manner, that causes it to send a permanently hot signal. As a result, causing the computer to incorrectly compensate for a lean signal.

Engine Overheating
Engine Overheating

All of which can result in overheating, and even misfires or engine ping. Also, it may not slow the ignition timing and turn on the cooling fans when necessary. Finally, causing the engine to overheat.

Illuminated Check Engine Light

An illuminated Check Engine Light is another symptom, of a potential problem with the (ECT) sensor. In many but not all vehicles, the computer can set off a Check Engine Light.

Check Engine Light
Check Engine Light

Usually, if it detects a problem with the sensor’s signal or circuit.

Poor Engine Performance Or Stalling

Your engine requires more fuel when, it is first started when cold. But, if it does not get the fuel, it will not idle smoothly. The signal from the (ECT) sensor tells the engine’s computer, when to apply extra fuel during a cold start. A faulty sensor can confuse the computer, keeping it from providing enough fuel. As a result, the engine may hesitate, stall, misfire or have poor engine performance.

Increased Emissions

If the sensor sends a faulty “cold” reading, the engine will run rich. As a result, carbon monoxide emissions will increase, and possibly hydrocarbons, as well. In contrast, if it sends a faulty “hot” reading, the engine may misfire and run rough, increasing hydrocarbon emissions.

How To Take Care Of Your (ECT)

Use these tips to help stay ahead of problems:

Do not use tap water to refill the radiator or the coolant reservoir:

  • Tap water contains elements of rust and other minerals, that might prove harmful in the long run. Especially, when the water boils and evaporates inside the radiator.
  • Coolant prevents the water from boiling. And, also lubricates the engine block and the radiator, preventing rust formation.

Keep On Top Of Any Leaks:

  • Fix oil leaks or gasket leaks immediately. Because, if oil leaks into the coolant, they do not mix. As a result, reducing the service life of the coolant temperature sensor.
Coolant Level Low
Coolant Level Low
  • Fix coolant leaks immediately. The cooling system in your vehicle is a sealed-type system. It is unusual if you constantly need to refill the reservoir with water. Consequently, if there is inadequate coolant in the system, the (ECT) sensor might get false readings.


The (ECT) sensor is one of the, most important engine management sensors. Because, the coolant temperature sensor is a crucial component, for ensuring your engine performs at an optimal level. For this reason, if you suspect that your  coolant temperature (ECT) sensor is having an issue, replace it.

Thank You !