How to check the sensors of the car?

The modern car is equipped with a large number of sensors. However, over time, they can fail. The motorist should know how to check them at home and when they need to be replaced. But if you have had an accident and your car is damaged so badly that it has no gauges left, the best way out of the situation is to scrap your car. You can do this here:

How to check the temperature sensor

First, you need to figure out how to check the temperature sensor, which is mounted in the cylinder head. If there are any problems, the corresponding indicator will light up on the dashboard. But there are indirect signs that tell you that it is out of order:

fuel consumption increases sharply,
the composition of the exhaust changed,
the steering of the car is reduced because the temperature of the engine rises,
the engine often overheats.

To check it, you need to know what is the resistance between the terminals at different engine temperatures. There is an inverse relationship – the higher the temperature, the lower the resistance. To check this, you have to pull back the rubber cover covering the terminals. The “plus” of the multimeter is connected to the conductor through which the signal is transmitted, and the “minus” to ground. The readings that the device shows when warmed up to a certain temperature are recorded. Each brand of car has its own table of normative values, which can be found in the technical documentation.

How to check the sensor with a multimeter
Most recommendations of motorists begin with recommendations on how to check the sensor with a multimeter. This device is also called a tester. Its peculiarity lies in the fact that it combines several functions at once. At a minimum, it can measure current and voltage, that is, it can be used as a voltmeter and ammeter. Gauges are devices connected to the electrical system of the car. Consequently, the multimeter will help to check whether the resistance value corresponds to the normative value. If it does not correspond – the device is out of order.

How to check the crankshaft sensor

The correct name for this device is the crankshaft position sensor. It is used to synchronize the work of the fuel injectors and the ignition system (in gasoline engines of the injector type). If this device fails, the ignition will turn on earlier or later than necessary, and the fuel mixture will not burn completely. It can also lead to unstable engine operation.

Before you check the crankshaft sensor, you should make sure that the car’s decreased dynamic performance is not caused by some other factor. The fact that it is the sensor that is the cause is indicated by arbitrary changes in the engine speed while driving. Problems may also occur in idle mode.

There are several ways to check. If possible, it is better to buy an inexpensive diagnostic scanner, there are quite affordable models. If during visual inspection on the end of the sensor no chips and heavy dirt is noticed, you can connect a diagnostic OBD-2 scanner to it. Modern devices work through mobile applications, sending there diagnostic fault codes.

Not everyone has such a scanner, so in its absence you can check the sensor with an ohmmeter (or multimeter) and oscilloscope. The last one gives the most accurate result, but not everyone has it either.

When checking with a multimeter, the resistance of the inductance coil is measured. The styli of the device are connected in pairs to its outputs without regard to polarity. The exact resistance of the coil can be found in the technical documentation according to it set the upper limit for the multimeter. If no significant deviations were found as a result of measurements, then most likely the sensor is okay. But you can duplicate the check, using already other methods.

How to check the coolant sensor: two ways

Sometimes this device is called a temperature sensor. Before you check the coolant sensor, you should take a modern voltmeter, or even better – a multimeter that can work in this mode. You should make sure that the wiring is functioning properly. In order for this device to cope with its tasks, the voltage on it should be stable, the normative value of 5 V. To check how things really are, you need to disconnect the wires from the device and with the motor running, measure the voltage applied to them with a multimeter working in voltmeter mode.

If there is no problem with the wiring, it means that the sensor itself is defective. To check it again take a multimeter, and to it are added an electronic thermometer and any electrical device capable of constantly heating water – for example, an electric kettle. A wrench can be used to remove the sensor.

There are two ways to check the coolant sensor. The first is by using all of the above devices, including a thermometer. To do this, an electronic (not mercury) thermometer is placed in the kettle with the water not yet heated. A multimeter working in ohmmeter mode is connected to the sensor and the device is placed in the kettle. The reading of the sensor is recorded. Then turn on the kettle and check resistance readings at key points – at +10 degrees and above, in increments of +5 degrees. They compare the obtained values with normative values, which can be found in the technical documentation. If the real values differ greatly, it is time to change the sensor.

The second way of checking does not involve the use of a thermometer, so it is less accurate, but it is more simple in execution. Its essence is to find the starting point, a known indicator – for example, 100 degrees at boiling water. This value can be taken as a reference point and the values can be determined at this point. This temperature corresponds approximately to a resistance of 177 ohms, but a small error is allowed, that is, in general, the value of the indicator should fall within the range of 190-210 ohms.

How to check the sensor

Motorists often wonder how to check the DMRV sensor. This name is deciphered as a mass air flow sensor. Therefore, it is called an air sensor in popular automotive publications. Ways to check it will be discussed below.

How to check the ABS sensor

This sensor is found in almost all modern cars. It is a non-contact device that analyzes the speed or speed of the wheel in cars equipped with active safety systems. The sensor provides the antilock braking system (ABS) and is also used by the directional stability system.

Before you test the ABS sensor, you should get a state-of-the-art multimeter with high accuracy and functionality. Ideally, it is best to have the sensor checked at a service station. There they will be able to do it using an oscilloscope, which will give more accurate results.

The test is carried out in the standard way. To do this, connect the device to the contacts and measure the resistance values. They must comply with the standard values prescribed in the technical documentation. During the test, it is also necessary to shake the sensor and wires several times. If the reading of the multimeter changes, then the problem is due to a break in the circuit.

The multimeter will also check the voltage. To do this, you only need to put it in the appropriate mode. But for this test, you should first use a jack to raise the car so that one wheel is in the air, and you could spin it up to 50 revolutions per minute. The standard voltage is 2 V.

How to check the air sensor

An important part of the car is the mass airflow sensor. It is abbreviated as DMRV. How stably it works determines the fuel consumption and power of the car. Before you check the air sensor, you need to remember where it is in order to return it exactly to its original place. The sensor is installed between the air pipe that leads to the throttle and the associated filter. The sensor is needed to measure the amount of air entering the cylinders. It transmits this information to the control unit. Based on the measured values, the “smart electronics” decides that it is necessary to increase or decrease the air flow into the mixture.

The malfunction of the device is indicated by certain signs. First of all, it is a signal on the dashboard, which calls to check the engine. It is also an increase in fuel consumption.

The most primitive, but quite reliable way to check is to forcibly disconnect the sensor and see how the running engine will work. Normally, it will function in emergency mode, which is indicated by a signal on the dashboard. You can not run the car with the sensor disconnected for a long time, but it is necessary to drive it. The car should accelerate faster. This will show that the problem is in the sensor. You can also use the classic test circuit with a multimeter.

How to check the speed sensor

The driver needs to know how to check the speed sensor and in what cases it should be done. Signs of malfunction of this device are:

lack of stability when idling,
failure of the speedometer (it either does not work properly or does not work at all),
Increased fuel consumption,
decrease of engine traction.

If an on-board computer is installed in the car, then everything is easier, because it will be able to immediately give a message that there is no signal.

What can cause the malfunction

Most often the failure is caused by a broken circuit, so first you need to make sure of its integrity. To do this, disconnect the power and check the contacts, whether they are free of oxidation or contamination. If there are such problems, the contacts need to be cleaned.

The fault may be caused by a broken wire near the plug, because that is where they bend the most. You should also check the resistance in the grounding circuit. The standard value is 1 ohm. If all of the above is done and the sensor is still defective, you should check the unit itself.


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