Is your car overheating?
Is the temperature gauge on your dashboard stuck at cold or hot?
Are you additionally experiencing poor vehicle idling and difficulty starting your engine?
If your answer to these is yes, then your temperature sensor could be the culprit, and you need to run tests on it to determine if it needs to be changed or not.
Without wasting time, let’s get right in.
What Is A Temperature Sensor?
A temperature sensor, or coolant temperature sensor, is a component within a vehicle that measures the temperature in the engine.
When measuring temperature, the coolant sensor sends either a hot signal or a cold signal to the Engine Control Unit (ECU), and the ECU uses these signals to perform several activities.
The ECU uses the data from the temperature sensor for proper fuel injection adjustment and ignition timing.
In some vehicles, the data from the temperature sensor is also used to trigger the engine cooling fan on and off, or supplied to a gauge on the car dashboard.
Symptoms Of A Bad Temperature Sensor
Due to the role a coolant temperature sensor plays in the engine and how it affects the functions of an ECU, the symptoms of a bad sensor are easy to identify.
- Vehicle Overheating
A faulty temperature sensor may send a permanent hot signal to the ECU, which means that when the engine needs cooling, there is no appropriate response from the ECU and the fan is never switched on.
The engine keeps heating up till it becomes overheated, and this could cause a fire hazard.
- Poor Ignition Timing
As mentioned earlier, the ECU also makes use of data from the temperature sensor to time ignition.
This means that, when the temperature sensor is bad, there will be difficulty starting the engine due to poor ignition timing.
- Inaccurate Fuel Injection
A bad temperature sensor causes bad fuel injection into the engine, which leads to a whole lot of other symptoms.
These range from black smoke coming out of the exhaust pipe to poor vehicle mileage, bad engine idling, and overall poor engine performance.
Keeping these conditions for a long time may result in your engine getting damaged.
Tools for Testing Temperature Sensor
There are two methods of testing a coolant temperature sensor and these methods have their specific tools and equipment.
To test a temperature sensor, you will need:
- A multimeter
- Hot and Cold Water
How To Test A Temperature Sensor With A Multimeter
Set your multimeter to DC voltage, take out the temperature sensor from your vehicle, place the red probe on the far right terminal, and place the black probe on the far left terminal. Dip the sensor in hot and cold water, and check the voltage readings on the multimeter.
This is the basic process of testing a temperature gauge with a multimeter, but there is a lot more to it.
- Find The Temperature Sensor
The temperature sensor is usually a small black device located close to the thermostat housing.
To locate the thermostat housing, you follow the hose that goes from the radiator into the engine.
At the end of this hose is the thermostat housing, and beside this is typically the temperature sensor.
This setup may vary based on car models but remains more common amongst modern cars.
For trucks, however, the temperature sensor could be found close to the metal cylinder at the engine block (intake plenum).
You have to take out this intake plenum to have access to it and hiring a professional mechanic is the safest bet so you don’t damage your engine.
- Take Out The Temperature Sensor
The temperature sensor is connected to the engine through a wired terminal.
It is connected to a wire harness through its metal terminals and you simply want to separate these two.
Just unplug the sensor from the wire harness.
P.S: Before opening your car’s hood to locate and take out the temperature sensor, ensure that the engine has been switched off and remained idle for at least 15 minutes. This is to ensure that it doesn’t burn you.
Once you have located the temperature sensor and removed it from the engine, your multimeter comes to play.
- Position Multimeter Leads
Place your multimeter leads on the terminals of your temperature sensor.
Some sensors may have up to 5 terminals, but ensure that the probes are placed on both ends of the sensor plug.
Using alligator clips makes the whole process a lot easier. When connecting multimeter probes, you don’t want them to be touching each other.
You simply clip the red probe to the terminal at the far right and clip the black probe to the terminal at the far left.
- Dip Sensor In Cold Water
Submerging the sensor in cold and hot water is necessary to get a reference temperature for measurements.
You get water of about 180ml, place ice cubes in it, and ensure it has a temperature of about 33°F (1°C). A digital thermostat could prove helpful.
- Take Measurements
Diagnosing a temperature sensor requires you to test whether it produces the right amount of voltage.
To do this, you set your multimeter dial to DC voltage and note down what the multimeter produces.
If the multimeter fails to produce readings, try readjusting the probes on the terminals.
If it still doesn’t produce any reading, then the sensor is bad and you don’t need to run further tests.
A proper reading from the multimeter is about 5 volts.
However, this depends on the model of the temperature sensor, so refer to your car’s manual. If you get a reading, note it down.
- Dip Sensor In Hot Water
Now, submerge your sensor in about 180ml of water at a boiling temperature (212°F/100°C).
- Take Measurements
With the multimeter still in the DC voltage setting, check for voltage readings and note them down.
In this boiling water test, a good temperature sensor produces a multimeter reading of about 25 volts.
Of course, this varies based on the model and you want to refer to the car or temperature sensor’s manual.
- Evaluate Results
Once you have run these cold and hot water tests, you compare the measurements you have taken to the requirements for your specific car’s model.
If the cold and hot measurements don’t tally, then the sensor is bad and needs to be replaced.
On the other hand, if they tally, the sensor is functioning properly and your problems may be from other components.
Here is a video that visually simplifies the process of running cold and hot water tests on a temperature sensor.
Testing Temperature Sensor Wires
You could test your sensor wires by using jumper cables to ground the wiring harness to a metal surface nearby.
Switch on your engine, ground the wire sensors using a jumper cable, and check your temperature gauge on the dashboard.
If the wires are okay, the gauge reads about halfway between hot and cold.
In case you can’t follow the wire way, we have a guide for that as well.
The temperature sensor is a small component that plays a very huge role in the health and performance of your engine.
If you notice symptoms, follow our steps and make use of a multimeter to measure the voltage produced from its terminals.
Hiring the service of a professional mechanic could prove useful if the steps seem a little difficult.
Frequently Asked Questions
How Do You Know If Your Temperature Gauge Is Broken?
Some symptoms of a bad temperature sensor include engine overheating, engine light illuminating, black smoke from the exhaust pipe, poor mileage, poor engine idling, and difficulty starting a vehicle.
Why Is My Temperature Gauge Not Moving?
The temperature gauge may not be moving because there are problems with the temperature sensor. The gauge may be permanently stuck on hot or cold depending on when the sensor got damaged.
How Do You Measure The Resistance Of A Temperature Sensor?
Set your multimeter to Ohms, place the probes on the terminals of the sensor preferably using alligator clips, and check for a resistance reading. The appropriate reading varies by sensor model.
Does Temperature Gauge Have A Fuse?
The temperature sensor doesn’t have a fuse of its own but uses the fused wire to the instrumental cluster. If this fuse is burnt, the temperature sensor does not work and the fuse should be replaced.