Dodge

ABC sensor - self-diagnosis, troubleshooting. Checking ABS sensors - personal experience. Checking the ABS sensor yourself. How to check the ABS sensor in different ways? How to measure the resistance of the abs sensor

Anti-lock brakes are present on almost all modern cars. This is due to high safety requirements, since ABS provides real assistance in case of emergency braking and difficult road conditions. Important elements of the system are sensors that record the speed of rotation of the wheels. Despite its high reliability and ability to work for a long time, the device sometimes breaks down.

Purpose and principle of operation of the ABS sensor

Anti-lock braking systems appeared on cars in the 70s, significantly increasing their safety during emergency braking. ABS consists of a control unit, a hydraulic unit, wheel brakes and speed sensors. The main device of the system is the control unit, into which sensor signals are received and processed. The data is analyzed and a decision is made to slow down or accelerate the wheels in the form of a signal to the valves of the hydraulic unit, which acts as a control.

When you press the brake pedal hard, the sensor detects that the wheel is locked and sends a signal to reduce the braking force, after which the brake fluid pressure drops and the wheel unlocks. If the brake pads are not released, the process will be repeated until the desired result is achieved. Thus, the operation of ABS is a cycle: braking - analysis - braking. The sensor itself controls the speed of rotation of the wheel.

The system is activated instantly, even before the wheel locks, which is indicated by the receipt of a signal on the instrument panel and is felt by characteristic shocks in the brake pedal. If a breakdown occurs, the brake system remains operational and operates normally.

Signs of a malfunctioning ABS sensor

The first sign of an ABS malfunction is a lit indicator on the instrument panel that does not go out for more than 6 seconds after turning on the ignition, or does not turn on when driving. A system breakdown is detected when the vehicle is moving at a speed of more than 25 km/h. There are quite a few problems that can happen with the anti-lock braking system, but the most common ones include the following:

ABS sensor wire is broken or the controller unit is damaged. In this case, an error is displayed on the instrument panel, the system is turned off, and signals about changes in angular velocities are not given.
The wheel sensor of the system has failed. When turned on, the system performs self-diagnosis and detects an error, but continues to function. The cause of the breakdown may be oxidation of the contacts, poor power supply to the sensor and a short circuit to ground.
Receipt from an additional device of information about different angular speeds of wheels at different tire pressures or different tread patterns, when the wheels brake differently.
Mechanical failure of elements - hub bearings, play and fracture of the rotor on the wheel sensor. In case of such failures, the system does not start. This also includes ABS pump failure.

The most vulnerable element of the system is the wheel sensor, which is located next to the rotating hub and axle shaft. Exposure to dirt and play in the hub bearings can damage the device, completely blocking the operation of the ABS. Along with the indicator signal on the instrument panel, the following signs indicate a sensor failure:

The on-board computer displays an ABS system error code.
There is no characteristic vibration or sound when pressing the brake pedal.
The wheels lock during emergency braking.
Appearance of the parking brake signal when it is disabled.

Checking the ABS sensor

If the ABS sensor malfunctions, the control unit stops receiving commands and the system stops working, which is determined by the wheels locking when braking. Possible malfunctions of the device are determined by the tester. To do this, you need the tester itself, a soldering iron and pins for repairs. The pins are connected to the connectors, and the device measures the resistance of the ABS sensor, which must correspond to the parameters specified in the operating manual.

If there is no resistance, then there is a short circuit in the circuit; if it tends to infinity, then there is an open circuit in the circuit. Full diagnostics of the sensor is carried out by ringing all its wiring, since one of the reasons for malfunctions is a violation of the integrity of the wires. A working device has the following indicators:

Insulation resistance – more than 20 kOhm.
Leg – front right ABS sensor, resistance from 7 to 25 kOhm.
Leg – rear right ABS sensor, resistance from 6 to 24 kOhm.

The sensors can also be checked in voltmeter mode. Each sensor is tested in turn using the following algorithm:

After jacking up the required wheel, connect the connectors of the PIN cable to the tester.
The wheel rotates at a frequency of 1 rpm.

A working sensor should give readings within 0.25-1.2 V. Increasing the wheel speed should increase the voltage reading. More informative information when testing the sensor can be obtained using an oscilloscope, but the device is quite expensive and requires special knowledge and conditions for maintenance.

ABS sensor repair

If a faulty ABS sensor is detected, it is dismantled, after which the issue of replacement or repair is decided. The cost of the device is quite high, and often there is a long wait for its delivery, which makes repairs quite feasible. The work is performed in the following order:

1. The sensor is disassembled by cutting off the part in which the measuring coil is located with a hacksaw. The body is carefully filed in a circle so as not to damage the fasteners.

2. The plastic casing protecting the coil is removed using a sharp knife and the winding is unwinded from the frame.

3. Wind a new coil with a wire of the same diameter. The RES-8 relay winding is suitable for this. The number of windings must provide the required resistance value - 0.92-1.22 kOhm. The work is carried out very carefully, since the wire is quite thin, and if it breaks, the process begins again.

4. The ends of the wires are soldered to the terminals, and the coil is effectively insulated from moisture using silicone or wax sealant.

5. The sensor is assembled by restoring the old housing. If the shell is critically damaged, it is made independently from the body of an electrolytic capacitor, suitable in size, and epoxy glue. A hole is made at the bottom of the body for the coil rod. After placing the updated part there, glue is poured.

6. After the glue has dried, the capacitor shell is removed, and the sensor mount is glued to its original place.

7. After the repair is completed, the sensor body is ground with sandpaper to accurately fit the socket. During the installation process, observe the following rules:

The core of the device is placed parallel to the teeth of the response disk and is controlled so that it does not overlap a pair of adjacent teeth;
A gap of 0.9-1.1 mm is left between the tooth and the core.

At the end of the installation, check the functionality of the system by starting the engine and making sure that the ABS indicator goes out 6 seconds after the start.

Replacing the ABS sensor

The procedure for replacing the sensor is quite simple, and it is not too expensive at a specialized service station. Replacing the device yourself is also quite possible. To do this, after purchasing a quality part, perform the following steps:

Using a jack, lift the corresponding wheel to provide access to the sensor.
Determine the location of the device and the method of its dismantling.
Unscrew the bolt holding the device in working position.
The sensor is removed and visually inspected for damage.
Install a new sensor.
All electrical connections are connected correctly.
Secure the device with the previously unscrewed bolt.
After installation is complete, you need to drive the car and test the operation of the system.

Using all the functions of a modern car does not exclude periodic breakdowns in sensor systems, which reduces the safety and quality of operation of the car. In particular, ABS sensors located on the wheel hubs often behave unpredictably. They are constantly exposed to dirt and moisture, which does not exclude their frequent failure. Every time the sensors begin to behave illogically again, it will be difficult to go to a service station and diagnose the system. In this case, you can go two ways. The first is to learn how to independently diagnose sensors using a computer and connecting a diagnostic program to an on-board diagnostic device. The second is to determine the malfunction of the sensors using other criteria.

If you have a laptop that can be used as a diagnostic device, you can easily find problems with these systems. All you need to do is connect the sensor diagnostics and start driving. The computer will show the speed of the wheel with a broken sensor at 0 kilometers per hour, the ABS on this wheel will try to constantly weaken the braking forces, even if you do not press the brake at all. If you don’t have a computer, you’ll have to differently determine possible problems with the sensors of this tricky brake force control system. Today we will look at diagnosing and replacing ABS sensors.

How to recognize that the ABS sensor is no longer performing its functions?

On older cars, a malfunction of the ABS sensor can lead to the most unpleasant consequences. If the wire breaks, the voltage may not reach the computer, just like when the wheel is locked. Therefore, a simple computer perceives this situation in such a way that one of the wheels is blocked. Ultimately, ABS begins to unlock one wheel during braking, which can completely disable the braking system, and in case of an emergency stop, provoke a complete loss of control, even causing the car to overturn. Signs that the ABS sensor is faulty are:

after inadequate operation of the system, the inscription “ABS” appears on the dashboard, the module stops working;
on modern cars, after starting the engine, the ABS light does not go out, and the system stops working;
during weak braking, the pedal vibrates, the brake force distribution system turns on;
auxiliary brake systems, amplifiers and balancing devices are constantly operating;
the on-board computer displays a number of problems that are related to the operation of the anti-lock braking system;
When connected to a diagnostic computer, an error code for the anti-wheel lock system sensor is read.

You can independently determine whether the sensor is faulty if the ABS light is constantly displayed on the dashboard. This is the main indicator that some sensor has stopped functioning and the system simply does not work. In this case, the first task of the motorist will be to check the integrity of the wires to the sensors. These wires often break due to stones being thrown into the hub area or other objects that cut the wire. Therefore, such a problem is not uncommon; almost all owners of cars with this module know it.

Methods for self-diagnosis of ABS sensors on cars

If you have a car with a more or less decent ABS system, then it may also contain self-diagnosis of this system. For example, on some BMWs, even old ones, there is a system that not every car owner knows about. After starting the engine, the ABS light comes on for three seconds, then immediately after it goes off, press the brake pedal five times. The self-diagnosis system will start, and the number of blinks of the light will tell you which modules in the anti-lock braking system were faulty. Read the instructions about the self-diagnosis capabilities of your machine. You can check the sensors in another way:

find the instructions for your car with electrical diagrams;
remove the connector from the ABS block;
find the so-called pinout of the ABS unit;
use a regular electrical tester;
check the resistance on the pins that are responsible for the sensors;
if the resistance shows a break, examine the situation on the wheel;
to do this, remove the wheel and find the system sensor;
measure the resistance on the incoming wires;
examine the wires for integrity.

This way you can determine which specific parts of the anti-lock braking system caused the malfunction of the entire module. With the help of such diagnostics, you can save a fair amount of money on car service costs. Even if replacing a sensor or wire yourself turns out to be a difficult task, you can come to the service with a request to replace a specific part, rather than carry out a full diagnosis. This way you will save money, at a minimum, on diagnostic services, as well as on correcting those faults that the diagnostic system finds (it’s no secret that they may not actually exist).

Is replacing ABS sensors on your own a realistic task?

In this case, many drivers prefer to turn to specialists, because this is an important system that can save lives in an emergency. However, changing the ABS sensor is quite simple. This procedure is not so expensive at a service station, so it will still be advisable to send the car for repairs. But if you want to service the system yourself, this is entirely possible. After the diagnostics have been completed, you will determine on which wheel the sensor is not working correctly. After this, simply read the section of your vehicle's manual to identify the warnings and follow these steps:

lift the required part of the car on a jack for good access to the sensor;
determine the location of the old sensor, as well as methods for its removal;
unscrew the bolt that holds the sensor in the required position;
remove the sensor from its place, examine it visually for damage;
directly replace the old sensor with a new one;
do not forget about the correct connection of electrical connections;
screw the sensor to its original place using the bolt that you unscrewed earlier;
Replace the wheel, drive the car and check the operation of the system.

In this case, an equally important process will be the purchase of a high-quality ABS sensor. The fact is that each car uses certain sensor features that cannot work in tandem with other parts. If you have a car that was bought second-hand, it is better to determine which ABS sensors are currently installed. You will not always find original factory elements on the hubs. It is quite possible that the previous owner has already replaced the sensors with cheaper ones, which caused the breakdown of this element of the electrical system of your car. The selection of the sensor is of great importance for the normal operation of the machine. Watch a video about replacing the ABS sensor on a first generation Renault Logan:

Let's sum it up

There are many breakdowns that can affect the ABS system. But the most common type of malfunction is sensor failure. If your car's anti-lock braking system is showing problems, the first thing you should do is check the sensors. There are several methods for testing the correct operation of these parts, so you can choose the most convenient testing option. However, diagnostics alone will not help the matter; any problems that have arisen will have to be corrected.

Today you can find and purchase ABS sensors from any manufacturer. You can find both simple parts for replacing factory sensors and original system elements at very affordable prices. And selection in this case will play a very important role. Use the factory catalogs to select sensors that are completely suitable for your vehicle and match the functions of the ABS system. To ensure that the anti-lock braking system does not interfere with the quality operation of the car, but helps to perform important tasks when braking, monitor the serviceability of the sensors and carry out diagnostic and repair work in a timely manner. Moreover, you can change the sensors of this system yourself. How often does ABS show problems in your car?

An anti-lock braking system is an essential component of any modern car. Not all domestic drivers are accustomed to this technical equipment. But some have already learned not only to take advantage of its benefits, but also to independently diagnose the operation of the system.

The essence of ABC is that during emergency braking, the movement of all four wheels is prevented from blocking. This works to increase vehicle stability and reduce braking distance. It is especially important when driving on slippery surfaces - gravel, icy, wet asphalt. The car does not skid, the level of controllability remains high, although the brake pedal is pressed to the limit.

ABS is a complex complex that is connected to the braking system.

Key parts are a hydraulic unit that modulates fluid pressure, wheel speed sensors, their location, and a computer that processes information from the sensors and transmits it to the main unit. Location: under the hood, in the space between the brake cylinders.

Method of operation of the anti-lock brake system

A strong press on the brakes is detected by sensors, and the system deciphers this as the car skidding. There is a signal about the need to reduce the braking force. The pressure of the special fluid in the brake line decreases, and the wheels are unlocked. Didn't succeed the first time? The system will continue to try until the brake pad tension is relieved. The operation of ABS is schematically: braking - analysis - disinhibition process.

The system's response speed is very high. It starts working even before the wheel locks. The driver sees a corresponding signal on the control panel and feels characteristic shocks in the pedal. If the warning message does not disappear from the screen, this indicates a problem.

You should not rely entirely on the system. It creates a false illusion of driving safety for the driver. It is not always possible to shorten the braking distance of ABS, especially when it comes to cornering. In addition, the system is difficult to predict. A motorist is rarely able to determine where his braking distance ends.

Should I be afraid of ABS malfunctions?This system does not need repair often, as it is equipped with fuses and special relays. Failure means that the brakes now work without additional control, but this does not directly affect their functionality. So you can drive a car with a problematic anti-lock braking system, but it’s better not to. Many drivers ignore the danger and overestimate their level of control over the vehicle. Even the most experienced motorist can make mistakes when braking in an emergency. So as soon as the first signs of a malfunction appear, repair it.

How to understand that the ABS is broken

In the simplest cases, the problem will be indicated by an indicator on the control panel. A sensor that lights up for 10 seconds turns on while driving and indicates a malfunction. In most cases, problems can only be identified while driving.

Individual failures are evident at a certain speed - 25 km/h.

Before a thorough search, you need to exclude two points:

recent tire change. Studded tires on the drive wheels increase the diameter, causing the rear and front elements to rotate at different speeds, which causes the malfunction sensor to light up;
The abs sensor can also trigger slippage.

False signals have been eliminated, let's move on to serious malfunctions.

Causes and symptoms ABS problems

The sensor wire broke and the controller unit broke. Signals about angular velocities are not transmitted, the error signal lights up, and the system turns off.
Wheel sensors are faulty. The system turned on, performed self-diagnosis, found an error, and continued working. The contacts have oxidized, the connection to the system power supply is broken. Another option is that the wheel sensors have shorted to ground.
Tires have different pressures, different tread patterns, and different degrees of rubber wear. One of the wheels goes slower than the others. Indications of angular velocity are transmitted by an additional device.
Mechanical damage to parts: separators and grilles may break, the hub bearing may wear out, play may appear, the wheel sensor rotor may break, and the operation of the pump may be disrupted. Mechanical causes of the malfunction prevent the ABS from even starting.

Most of the above problems can be solved on your own. After all, complete replacement of equipment is very expensive. As the experience of auto mechanics shows, wheel sensors break more often than other parts. They are located next to the hubs and take on all the dirt. By examining them, you can begin the diagnosis.

The most unpleasant thing that can happen is that the control unit turns out to be faulty. And it is very expensive. But the complex works with a protective relay and rarely creates problems for the motorist. Therefore, you can check the block last. The procedure begins with the front wheels:

remove the sensor, clean with kerosene, white spirit;
checking the ABS sensor involves a thorough inspection of the wheel hub teeth. The revolutions are read from them. Dirty, clogged teeth - incorrect information and system freeze;
remove and clean the reverse gear sensor;
how to check if the electrical resistance is correct? Compare with the readings from the car's factory manual:
lift the body with a jack, spin the wheel, and while rotating, measure what voltage passes through the sensor winding. Compare with indicators from the directory;
check the bearings. A worn hub is one of the most common causes of problems. After cleaning with kerosene and checking by shaking, the faults will become obvious. Replace parts if necessary. Use a multimeter to check the operation of the sensor.

Did the procedure fail? The next step is checking the protective relay. Its location is indicated on the car wiring diagram. The device has aluminum walls and a plastic cover. There are a couple of fuses inside and it is quite possible that one of them simply burned out. When buying a car on the secondary market, you need to inquire about the location of the protective relay from the previous owner.

Are the fuses ok but the system is still faulty? Let's diagnose the relay itself:

disconnect the electrical connector;
connect the voltmeter probes to the first two numbered block pins;
turn on the ignition, measure the network voltage - 20V. There is no voltage - check the negative connector to see if the connection has gone to ground of the car;
remove the relay, connect to the battery (terminals number 5 and 6). Give 12 V. Clicks are heard - the device is working, if not - it needs to be replaced.

Checking the abs sensor

The first thing is to remove the dirt. The next step is to measure the voltage in the node. The norm is 800-1200 Ohms, but there are nuances, it is better to check the factory data in the manual. The network grows endlessly - a sign of a break. Resistance is zero - there is a short circuit in the circuit.

All wiring must be tested. Here are the indicators that are considered acceptable: insulation - 20 kOhm or more, legs - from 6 to 25 Ohm.

Sensor problem? It needs to be replaced with a new one. If the entire system is examined, but a fault is not found, then the problem is in the control unit. You shouldn't try it yourself - you'll have to get it checked to a service station and have it repaired by qualified technicians.

Sometimes while driving, a car's gasoline engine begins to make a suspicious metallic knock. Drivers call it "tapping fingers." This sound is a sign of detonation, an extremely undesirable phenomenon that can lead to engine failure and the need for costly repairs. To prevent this from happening, a knock sensor is installed on the cylinder block. If it breaks, you can check it with your own hands.

How the sensor works

The phenomenon of detonation occurs for various reasons. This includes the use of low octane gasoline, a high compression ratio, and many other factors. What matters is driving in certain gears, the degree of soot, and the presence of certain components in the working mixture.

The knock sensor is an accelerometer that analyzes the mechanical vibrations of the cylinder block and converts them into electrical impulses. The principle of operation is simple: the device constantly sends signals to the electronic control unit of the power unit. That, in turn, changes the composition of the mixture and the ignition timing depending on these signals. The result is proper use of resources and engine operation at optimal power.

How to understand that it is out of order

The product is installed in cars with an electronic control circuit. Diagnosing faults in such machines is simple - if everything works correctly, the sensors on the dashboard remain inactive. The main sign of a malfunctioning knock sensor is the appearance of the inscription “Check engine” (CHECK). It can burn constantly, or it can appear and disappear.

If the sensor breaks down, acceleration performance deteriorates. The car starts, but works worse - it accelerates poorly, vibration occurs at rpm below 1000, power drops and fuel consumption increases, and the amount of smoke from the exhaust increases.

Why is this happening? Sensor malfunctions are related to automotive electronics. The following reasons are possible:

the signal wire is broken;
a short to ground has occurred;
there was a short circuit in the on-board network of any wire of the device;
the shielding braid is damaged;
the power unit control unit has failed;
something is damaged inside the sensor itself.

Checking the knock sensor

Since breakdowns occur for various reasons, you will have to check several elements of the system. Inspect the condition of the sensor wires, check the harness sockets and sensor plugs. Evaluate the reliability of their connections. If everything is in order here, check the contacts of the socket. Found damaged components? Replace them. It is also recommended to examine the condition of the tourniquet. Turn off the ignition, disconnect the harness from the sensor and check it with an ohmmeter. This way you will know if the chain is intact.

Sometimes the problem lies in the condition of the shielding braid. In this case, we proceed as follows.

We look to see if the harness sockets and plugs are securely connected;
We study each of their components;
We check whether the shielding braid is intact.

If the cause of the malfunction is a short to ground, you must proceed using another method:

We disconnect the entire block from the harness, along with the knock sensor;
We check the integrity of the chain, look for heavily worn places;
Turn off the ignition and, using an ohmmeter, examine the place where the engine mass is connected to the harness circuit.

We find and dismantle the sensor

Checking parts for one or two wires using a multimeter

The first thing to do is to find out what resistance is typical for a properly functioning sensor in a particular car. The figure varies greatly among different manufacturers.

This is interesting: resistance indicators can be the most unexpected. So, in VAZ cars with injection engines it is almost impossible to measure it because the indicators are too high. In Nissan and Subaru the figures are about 550 kOhm, in Hyundai - about 5 MOhm (megaohm).

To carry out the tests, you will need a multimeter, and a fairly sensitive one, as well as a socket wrench of size “13” or “22”, depending on the size of the installed sensor. To test resistance, switch the tool to kOhm resistance mode and attach it to the probe. If a two-pin sensor is installed in the car, the connection is made to the terminals; in the case of a single-contact model - to the contact and the body.

Now lightly tap the sensor with a metal object - a screwdriver or bolt. Pay attention to the multimeter readings. If there are deviations from the values specified in the instructions, a breakdown has occurred.

It is recommended to check whether there is voltage at the electrical ends. Disconnect the electrical connector of the sensor and remove it from the engine. Switch the multimeter to millivolts and connect the “+” probe to the signal pin. The “-” probe must be connected to the sensor ground. This part is easy to recognize - it is a hole through which the mounting bolt to the motor passes.

Hold the sensor in your palm and lightly tap it on a surface. The result should be a voltage - typically between 30 and 40 mV. If no potential difference occurs, then the sensor has failed.

There are no particular differences in testing for broadband and resonant sensors.

We connect the sensor to the multimeter and knock it on a hard object

Diagnostics with a dial tester or voltmeter

In addition to a multimeter, you can use a pointer tester - the actions are similar to working with a multimeter.
There is another way. With the engine idling, connect an AC voltmeter to the sensor. Tap the knock control component with a hard, non-metallic object. If the voltmeter shows that the signal amplitude from the device is below 0.1 V, the device is faulty.

Video on how to check

Repair or replacement?

You decide. The cost of the product depends on the car model and the manufacturer of the component - for a replacement you will need to pay an amount approximately equal to its price. You can change the device yourself; for this you will need a room with a pit. Self-repair is also possible: if you are well versed in cars, it will take no more than an hour.

September 27, 2017

The task of the anti-lock braking system (ABS), installed on the vast majority of modern cars, is to prevent the car from skidding during heavy braking. To do this, a special device is built into each hub, transmitting information about wheel rotation to the electronic control unit. Since a malfunction of this element is often the cause of system failure, the car owner should know how to check the ABS sensor in a garage.

Briefly about the principle of operation

The ABS function simulates the harsh, repeated pressure on the brake pedal experienced by drivers of older cars on slippery roads. Electronics uses this method of braking much more efficiently, locking and “releasing” the wheels several times per second. The operating algorithm is as follows:

During sudden braking, the control unit monitors the behavior of the wheels using sensors.
If one or more wheels stop rotating, the ECU issues a command to a hydraulic valve that releases fluid from that circuit. The pads stop holding the disc and rotation resumes.
By comparing the readings of all meters, the controller makes sure that braking is not complete and closes the hydraulic valve, and the wheel is blocked again. The cycle, lasting a fraction of a second, is repeated until the machine stops completely.

Important! If the functionality of one or more sensors is impaired, the ABS will fail entirely, since the electronic unit will not be able to compare the behavior of the wheels.

The latest generation ABS sensor is a coil with a semiconductor element installed in a stationary part of the hub. In the immediate vicinity of it, a toothed ring is attached to the brake disc, whose rotation is monitored by a sensor. It happens like this: the controller supplies voltage to the device, and it constantly changes the resistance due to the passage of a series of teeth on a rotating ring.

When the amount of electrical resistance becomes constant, the ECU regards this fact as wheel locking and turns on the above-described algorithm. If the element fails, the ABS system is completely disabled.

Signs of sensor malfunction

The following symptoms indicate that the ABS sensor needs to be checked:

when braking sharply or on a slippery road, the car moves “skid” and goes into a skid;
there is no characteristic sound of ABS activation - frequent tapping or crackling from the side of a locked wheel (the type of noise depends on the make of the car);
The anti-lock braking system warning light on the dashboard lights up.

If, for various reasons, the functionality of several sensors is disrupted, then the indicator for turning on the handbrake or a malfunction of the brake system additionally flashes on the instrument panel. You can continue to operate the car, but in slippery areas or during an emergency stop, the driver will have to work instead of ABS - often and sharply press the pedal.

How is the check performed?

Since the operation of a working ABS sensor is based on changes in electrical resistance when the wheel rotates, its parameters can be measured with a multimeter or a tester operating in ohmmeter mode. Conditions for diagnostics: a regular garage or a flat area, an inspection ditch is not required. From the tools, take a jack and a wheel wrench.

To check the ABS sensor with a tester, follow these steps:

Place the car on a level surface and secure it with wheel chocks. The handbrake should not be applied.
Jack up the rear wheel and remove it. Having found the wiring harness going to the sensor in the hub, find the connector and disconnect it. Clean all contacts thoroughly, preferably with a special liquid.
Turn on the multimeter to measure resistance and take measurements in the block coming from the sensor. Depending on the brand of car, the value should be from 500 Ohm to 1.4 kOhm.
Grab the drum or disc with your hand and spin it while watching the tester readings. The resistance must change.
Switch the device to voltage measurement mode and turn on the ignition. Check the presence of DC current from the control unit by connecting a multimeter to the second part of the connector.
Repeat the operation on all wheels.

On different car models, the connector may be located in different places - hidden under the bottom or plastic protection. To locate the block, probe the wiring harness by hand.

Analysis of diagnostic results

The problem with the ABS function does not always lie in the sensors. The culprits of system failure may also be the wires connecting the elements to the control unit. That is why it is necessary to carry out 3 measurements and draw the following conclusions based on the results:

If the resistance of the ABS sensor tends to zero or, conversely, the device shows an infinity symbol, then there is a malfunction of the element itself. Another option is a violation of the insulation or a break in the section of conductors from the connector to the sensor.
The tester shows that the resistance is within normal limits, but when the brake disc rotates, its value remains constant. There are two versions here: severe contamination of the gear ring (as an option - destruction) and, again, failure of the sensor.
The absence of voltage in the supply line indicates a break in the electrical circuit coming from the controller.

In the first case, it is necessary to remove the device from the hub and inspect the wires for fractures, breaks or short circuits. To be sure, measure the resistance again, while moving the conductors. If the result is negative, buy and install a new part.

If the resistance remains the same, get to the gear ring, clean it thoroughly and inspect it. If you find mechanical damage, it is better to replace the spare part.

Advice. Sometimes unscrupulous or ignorant auto mechanics damage the ring when repairing the suspension, or even throw it away completely. When picking up your car from a mechanic, always check that this important part is present.

In the case when there is no voltage in the controller circuit, you should ring this section of the wiring. How to do it:

Find out where the electronic control unit for the hydraulic valves is located. For example, in a Chevrolet Aveo it is located behind the brake fluid reservoir, and in a Renault Megane it is located on the side of the alternator drive belt.
Remove the block from the ECU and clean the contacts. Find the pinout of the wires or track them by color.
Place a shorting jumper on the block located near the wheel. Test the circuit with an ohmmeter or a regular light bulb with a battery.

The easiest way to find the ECU if there is no documentation for the car is to follow the brake pipes leading to the hydraulic unit. The latter stands next to the controller or is connected to it by a bundle of wires.

If an open circuit is detected, you will have to look for the defect along the entire line in order to eliminate it. The work is quite complex, so it should be entrusted to an experienced auto electrician.

Alternative verification method

When you don't have a multimeter at hand, you can check the ABS sensor in a simpler way. It will work when only one element fails, and not several. Diagnostics is performed as follows:

Disconnect the connector on one wheel sensor. Next, you need to start the engine and drive a few meters.
If the second light on the brake system (or handbrake) malfunctions comes on, then the element being tested is operational. Connect the block and repeat the operation on the next wheel.
If one sensor is broken, the ABS indicator lights up, and if there are two or more sensors, the handbrake lamp lights up. When the second indicator on the panel does not light up, it means that you have disconnected the faulty element.

The method allows you to determine the location of the problem, but not its nature. For a more accurate diagnosis, you need to use a tester with an ohmmeter.