How To Test A Coolant Temperature Sensor With A Multimeter

In a car, an internal combustion engine will normally have a hot engine. This is a natural result of using rapidly occurring explosions of fuel combined with air to produce the locomotion that drives the wheels. As a result, the engine has to be cooled, and this is where the engine cooling system comes into play. The coolant is the most important component of this system.

In olden times, this used to be water, occasionally combined with antifreeze in the winter to prevent the engine block from turning into an engine block of ice. Technology advancements led to the replacement of plain water as the principal cooling liquid as well as the development of sensors to measure the coolant’s temperature. Testing a coolant temperature sensor with a multimeter is a valuable diagnostic step when dealing with issues related to engine performance, fuel efficiency, or cooling system problems in a vehicle.

In this guide, we will explore how to use a multimeter to test the coolant temperature sensor, helping you identify whether it’s working correctly or if it needs replacement to maintain your vehicle’s performance and reliability.

What Is A Coolant Temperature Sensor?

The coolant temperature sensor provides the engine control unit with information about the engine’s operating temperature so that the amount of fuel and ignition point may be adjusted appropriately.

To measure the engine’s operating temperature, coolant temperature sensors were created. Simply put, the sensor outputs a little charge that the engine control unit can read. This charge is produced when the voltage passes through the internal resistance of the sensor, which decreases when the temperature rises and vice versa. The ECU can determine the temperature recorded by measuring the impact of the changed resistance.

Symptoms Of A Faulty Engine Coolant Temperature Sensor

There are several problems that point toward the coolant temperature sensor being damaged.

A defective coolant temperature sensor can manifest itself in many ways through fault detection by the control unit and the resulting emergency program strategy.

Common fault symptoms include:

• Increased idling speed
• Increased use of gasoline
• Inadequate first behaviour

Moreover, issues with the exhaust gas test cycle may arise from elevated CO levels or a lambda control interruption. The control unit’s fault memory has space for the following entries:

• A sensor short circuit or a short circuit from frame to frame in the wiring
• Positive wiring failure or break
• Improbable signal changes (signal jump)
• The engine fails to heat the coolant to the required level.

Tools You’ll Need

• Digital Multimeter
• Kitchen thermometer
• Wrench (ratchet and socket set, if you need to remove components)
• Paper and pencil

Locate the Coolant Temperature Sensor

To locate the coolant sensor, lift the hood of your car.

• The sensor may be mounted on your car’s cylinder head or intake manifold. However, one of the most familiar places is on or near the thermostat housing.
• You can find the top radiator hose, which joins the thermostat housing on the engine side, which connects to the thermostat housing on the engine side.
• On most current automobiles, look for a large nut with an electrical connector on top, and one or two electrical wires coming from the connector (on earlier vehicle types).
• In big vehicles, in particular, several sensors are hidden beneath the intake plenum, requiring the removal of the intake merely to reach them.

Consult your car’s service manual if you’re still having difficulties finding the ECT sensor. In most auto parts stores or online, you can get a service handbook for the specific make and model of your vehicle

How To Test A Coolant Temperature Sensor With A Multimeter

There are a few ways to test for a faulty coolant temperature sensor. Often, the first concrete indication of a faulty coolant temperature sensor will be OBD II error codes from the ECU. P0115 to P0119 are the codes connected to this. Follow these instructions if you see one of these errors or have any other reason to believe that the coolant sensor is causing your problems.

Locate the sensor: By necessity, the sensor is often located close to the front of the engine.

A good place to start is the thermostat or radiator housing. If necessary, use a light. Consult the technical manual for your car if you can’t find the sensor.

Examine the wiring. If there are problems with the electrical connections, plugging them in might be the answer. This is most often the result of an improperly installed connection or damaged or corroded cables and wires.

Check the wire harness for the sensor with a multimeter. To do this, unplug the cables that are attached to the sensor. Then, without starting the engine, turn the ignition key. Attach the multimeter’s red wire to terminal two and the black line to ground it. There is no issue on this end if the value is up to 5 volts.

Check the sensor with an ohmmeter: While the ignition is off, disconnect the sensor’s cabling. Connect the terminals of the ohmmeter to the sensor. Record the resistance measurement. Rewire the system. After around two minutes of operation, restart the engine. Next, turn off all of the previous connections, then gauge the resistance. In contrast, examine the data from a cool engine. At least 200 ohms should separate the two. If this is not the case, then the sensor is malfunctioning.

To test the sensor, use a multimeter. Record the voltage. Often, this is 5 volts or less. After reattaching the sensor, let the engine run for about two minutes before shutting it off. Reassess the voltage after disconnecting everything. When the motor has warmed up, it should be as low as 0.25 volts. A defective coolant sensor is indicated by no change in voltage.

You may replicate hot and cold readings if your motor won’t start by submerging the sensor in hot and cold water. Make sure the sensor has enough water resistance, and avoid immersing the terminals. Take your readings using water that is both cold and just boiling. While removing the sensor, make sure your car is off and the key is not in the ignition. You will be protected from electrical shock by doing this.

The technical literature or internet resources can provide more precise information about the voltages and resistances that can be anticipated from your coolant temperature sensor. If you are unclear about the received values, refer to these numbers.

Replacing A Defective Sensor

• Unfortunately, you have to buy a new coolant temperature sensor because a damaged one can’t actually be fixed. Thankfully, they are not overly expensive. The replacement procedure is rather easy to do at home:

• Find the previous sensor. You already know where the coolant temperature sensor is if you’ve checked to see whether it’s broken. If not, proceed to step 1 in the troubleshooting section.
• Remove the previous sensor. Unplug the connection slowly.
• The old sensor is unfastened and removed. To unscrew the gadget, you’ll need the right tools. Before unscrewing it by hand, spin it anticlockwise using a ratchet with a deep socket.
• The new sensor is installed. After cleaning the area, put the new sensor in the appropriate tool.
• Install the new sensor. Connect the formerly unplugged connection.
• Examine the sensor. Start the engine while keeping an eye on the dashboard’s temperature indicator.

Conclusion

Testing a coolant temperature sensor with a multimeter is a straightforward process that can help you maintain your vehicle’s performance and prevent potential engine issues. By following the steps outlined in this guide, you can diagnose problems, ensure accurate temperature readings, and address cooling system concerns promptly. Regular maintenance and troubleshooting like this not only save you money but also contribute to the longevity and efficiency of your vehicle. Remember to consult your vehicle’s manual for specific details and specifications, and always prioritize safety when working with automotive components.

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