When your ‘Check Engine Light’ is blinking, it doesn’t mean that your entire engine is busted. There are plenty of reasons why that is and one of them could be an error or a problem in your Engine Coolant Temperature Sensor.

What is Engine Coolant Temperature (ECT) Sensor?

Troubleshooting the Engine Coolant Temperature Sensor ProblemsAn ECT Sensor is a pin—about two inches long—that monitors the temperature change inside your car engine. It is also called as the engine’s ‘master sensor’ since it detects the change in the temperature inside the engine. Your engine has coolants inside the cylinder heads and engine block that regulates the temperature when the engine is running. The ECT sensor checks if the coolants are working properly in cooling the heat caused by friction inside the engine. Every change in temperature detected by the ECT signals the Powertrain Control Module (PCM). It indicates if the engine is cold, warming up, steady at the normal temperature, or overheating.

On your dashboard, it is the indicator that looks like a key with three pins floating on the liquid. It serves as your engine’s thermistor and it is the indicators for your cars proper operating strategy. The engine’s cooling system also affects the performance of the fuel, ignition, emissions and drivetrain functions. If the ECT sensor fails to function (i.e. malfunctions or give false readings) then it can distress a lot of things.

Where is the ECT sensor located?

Troubleshooting the Engine Coolant Temperature Sensor ProblemsThe ECT sensor is found in different places within the engine depending on the vehicle. Typically, it’s near the thermostat housing inside the intake manifold. Some may be found in the cylinder head. Other engines—like the V6 or the V8 engines—have two ECT sensors. They are located in the cylinder banks.

The sensor’s tip is always in direct contact with the coolant to allow a more accurate reading. However, if the coolant level is low, the sensor’s readings may be affected greatly.

What are the symptoms of a faulty ECT sensor?

The ECT plays a crucial role in indicating the proper functioning of engine roles. A faulty sensor will cause internal engine problems to go worse, for example, it can cause cold driveability, induce emission problems, increase fuel consumption and even prevents the engine management system to a closed loop.

Take note of the following indicators for a faulty ECT sensor problem:

Lit Check Engine Light

Once your Check Engine Light flashes on, there is a possibility that your ECT sensor circuit or wiring is faulty. The Check engine Light will remain lit up until the problem in your engine is fixed.

Overheating engine

Overheating is the result of a faulty signal delivery by an error in your ECT sensor. If for example, your ECT sensor sends a permanently hot signal instead of a permanently cold signal then this will cause the computer to compensate for the wrong signal. Your engine may overheat, may even have a misfire or an engine ping.

Nasty emissions

Troubleshooting the Engine Coolant Temperature Sensor ProblemsNobody wants his car to puff black smoke especially not you. Black smoke emissions may be a symptom for a problematic ECT sensor. Faulty sensors can confuse the computer into performing its proper function like regulating the fuel mixture for the engine to burn. If a faulty sensor sends the wrong signal then the computer may increase the fuel mixture it feeds into the engine. If this happens and the engine cannot burn the excess fuel it will burn up in the exhaust pipes instead and turn to black smoke. TAKE NOTE: Black Smoke Emissions are never a good sign for your car.

Inefficient Fuel Economy

A defective sensor can cause miscalculations done by the computer and this includes the feeding of the fuel into the combustion chamber. Faulty sensors may cause the computer to make incorrect calculations in timing and fuel feed. If an ECT sensor sends a permanently cold signal then this will trick the computer into making the engine warmer—even if it’s actually the right temperature. It will cause the computer to unnecessarily produce more fuel resulting to reduced and poor fuel economy as well as prevent an efficient engine performance.

Slow Engine Warm-up

A defective sensor will not be able to perform well especially if it reads the proper temperature slower than it should. A slow reading may cause other engine functions to compensate for a slow reading and faulty reading resulting to multiple issues such as overheating, engine misfire and the like.

What are the causes ECT sensors to fail?

Faulty wiring. Old cars have the tendency to wear out and constant changes in the temperature, the frequent use and maintenance, the wiring of the engine may be gravely affected including the ECT sensor’s wiring.

Improper installation. In cases where the ECT sensor was not properly placed inside its hub will cause a problem. This will prevent the sensor from making proper readings since it may not be directly attached to the coolant. This may also make the ECT sensor more prone to corrosion.

Connector problems. Signals sent by the ECT sensor to the computer may be affected due to loose wiring. The problem may not be found on the sensor itself, it may just be that the wiring was either loosely disconnected or completely disconnected from the sensor.

Corrosion. The ECT sensor is just as sensitive as other parts of the engine. Like all other metal components of the engine exposed to different chemicals and chemical reactions, the ECT sensor is prone to corrosion. Corrosion is caused by lack of maintenance or simply just because the engine or the vehicle is already getting old.

Open Thermostat. The thermostat can also be a problem especially if it is stuck open. This causes the sensor to make slow reading thus preventing the engine to warm-up properly.

How To Diagnose an ECT sensor problem?

There are different codes that correspond to different ECT functions. Nowadays, vehicles come with an OBD II onboard diagnostic system in order to indicate internal engine problems. An OBD II emissions test will definitely catch faults in the ECT sensor and turn on the Check Engine Light or the Malfunction Indicator Lamp (MIL). Every time it catches a problem, it relays a trouble code:

P0115 or Engine Coolant Temperature Circuit. This indicates that the Powertrain Control Module or PCM is detecting an abnormally high or low voltage condition in the ECT.

 P0116 or Engine Coolant Temperature Circuit Range/Performance. The PCM expects the ECT signal circuit to gradually make resistance changes according to the engine’s rising temperature as it warms up. If the PCM happens to detect a dramatic change in voltage that doesn’t correspond with the engine warming up then the P0116 code will set.

P0117 or Engine Coolant Temperature Circuit Low Input. This code sets when the PCM detects a signal voltage lower than the normal range usually indicated by the sensor.

P0118 or Engine Coolant Temperature Circuit High Input. This code sets when the PCM detects a signal voltage higher than the normal range usually indicated by the sensor.

P0119 or Engine Coolant Temperature Circuit Intermittent. When the ECT sensor sends erratic or intermittent signals to the PCM in a set period of time given certain circumstances then the trouble code P0119 sets.

Troubleshooting the ECT Sensor

Most of the reasons that make a faulty ECT sensor are due to physical damages caused by cracks major corrosion or leaks from the coolant. However, in order to check the ECT sensor defect would rely mostly on measuring its resistance and voltage. Here are simple ways in order to check if your ECT sensor is faulty.

Checking the ECT sensor harness with a MultiMeter

This allows you to check if the harness that receives the signals have a problem in relaying the signal to the computer this will rule out any faulty wiring.

  1. Pull out the harness connected to the sensor to reveal the connection point between the harness and the sensor
  2. Turn the ignition key on without starting the engine.
  3. Connect the red metal rod to terminal two while stick the black tip to any other metal to ground on any other metal point in the vehicle.
  4. If the MultiMeter reads at most 5 volts then the harness has no problem.

Checking the ECT sensor with an ohmmeter or Digital Volt-Ohm meter (DVOM) or MultiMeter

  1. Screw the sensor out with a wrench.
  2. Set your MultiMeter in Zero Ohms.
  3. Touch the two metal prongs in the sensor with the two pins from the MultiMeter.
  4. If there is no reading then the sensor has a problem but if it reads between 1.5 to 2 Ohms then your ECT sensor is working well.

To verify if your sensor is working, heat a pot of water and partially dip the sensor in the water. Stick the pins on the sensor’s prongs and check if the reading from the ohmmeter goes down. If it does, then your ECT sensor is fine but otherwise, then it has faulty readings.

Replacing an ECT sensor

  1. Remove the harness connected to the ECT sensor.
  2. Carefully screw the sensor out with a wrench.
  3. Clean the surrounding area where you will put a new sensor in.
  4. Grab a clean ECT sensor and carefully screw it in with a wrench.
  5. Secure the harness.

The Engine Coolant Temperature Sensor or Master sensor is a vital indicator that monitors almost every important aspect of your vehicle and knowing what it is and what causes it to malfunction will serve your vehicle a longer lifespan.