ABS sensor resistance. Diagnostics and principle of operation of the abs sensor Is it possible to ring the abs sensor

The presence of ABS in a vehicle greatly increases traffic safety. Gradually, car parts wear out and may become unusable. Knowing how to check the ABS sensor, the driver can identify and fix the fault in a timely manner without resorting to the services of a workshop specialist.

How ABS works on a car

Anti-lock braking system (ABS, ABS; eng. Anti-lock braking system) is designed to prevent car wheels from locking.

The primary purpose of ABS is preservation control over the car, its stability and controllability during unexpected braking. This allows the driver to make sharp maneuvers, which significantly increases the active safety of the vehicle.

Since the friction coefficient is reduced in relation to the rest coefficient, the car, when braking on locked wheels, will travel a much greater distance than on rotating ones. In addition, when the wheels are blocked, the car skids, depriving the driver of the chance to carry out any maneuver.

The ABS system is not always effective. On an unstable surface (loose soil, gravel, snow or sand), the immobilized wheels form a barrier of the surface in front of them, breaking into it. This significantly reduces braking distance.A car with studded tires on ice travels a greater distance when the ABS is activated than on locked wheels. This is explained by the fact that rotation prevents the spikes from crashing into the ice and slowing down the movement of vehicles. But at the same time, the car retains controllability and stability, which in most cases is much more important.

Wheel speed sensors are installed on the hubs

Equipment installed on individual vehicles allows the function of disabling ABS.

This is interesting! Experienced drivers on cars that are not equipped with an anti-lock device, when unexpectedly braking on a difficult section of the road (wet asphalt, ice, snow slurry), act on the brake pedal jerkily. In this way, they avoid complete wheel lockup and prevent the car from skidding.

ABS device

The anti-locking device consists of several components:

Speed meters (acceleration, deceleration);
Control magnetic shutters, which are part of the pressure modulator and located in the line of the braking system;
Electronic monitoring and control system.

Pulses from the sensors enter the control unit. In the event of an unexpected decrease in speed or a complete stop (blockage) of any wheel, the block sends a command to the desired damper, which lowers the pressure of the fluid that enters the caliper. This weakens the brake pads and allows the wheel to move again. When the wheel speed equalizes with the rest, the valve closes and the pressure in the entire system equalizes.

General view of the ABS system in a car

On new cars, the anti-lock braking system activates up to 20 times per second.

The ABS of some vehicles includes a pump, the function of which is to quickly increase the pressure in the desired section of the highway to normal.

This is interesting! The effect of the anti-lock braking system is felt by reverse shocks (impacts) on the brake pedal when there is strong pressure on it.

Based on the number of valves and sensors, the device is divided into:

Single channel. The sensor is located in the differential area on the rear axle. If even one wheel stops, the valve reduces the pressure on the entire line. Found only on older cars.
Dual channel. Two sensors are located diagonally on the front and rear wheels. One valve is connected to the main line of each bridge. It is not used in cars manufactured according to modern standards.
Three-channel. Speed meters are located on the front wheels and the rear differential. Each has a separate valve attached to it. Used in budget rear-wheel drive models.
Four-channel. Each wheel is equipped with a sensor and its rotation speed is controlled by a separate valve. Installed on modern cars.

Main types

ABS sensor with read by the primary measuring part of the anti-lock braking system.

The device consists of:

A meter placed permanently near the wheel;
An induction ring (rotation indicator, impulse rotor) installed on a wheel (hub, wheel bearing, CV joint).

The sensors are available in two versions:

Straight (end) cylindrical shape (rod) with a pulse element at one end and a connector at the other;
Angled with a connector on the side and a metal or plastic bracket with a hole for a mounting bolt.

Two types of sensors are available:

Passive - inductive;
Active - magnetoresistive and based on a Hall element.

Passive

They are distinguished by a simple operating system, but are quite reliable and have a long validity period. Does not require a power connection.An inductive sensor is essentially an induction coil made of copper wire, in the middle of which there is a stationary magnet with a metal core.

The meter is located with its core to the impulse rotor in the form of a wheel with teeth. There is a certain gap between them. The rotor teeth are rectangular in shape. The opening between them is equal to or slightly larger than the width of the tooth.

While the transport is in motion, as the teeth of the rotor pass near the core, the magnetic field penetrating through the coil is constantly changing, forming an alternating current in the coil. The frequency and amplitude of the current are directly dependent on the speed of the wheel. Based on the processing of this data, the control unit issues a command to the solenoid valves.

The disadvantages of passive sensors are:

Relatively large dimensions;
Poor accuracy of readings;
They begin to function when the car picks up speed over 5 km/h;
Triggered by minimal wheel rotation.

Due to frequent errors, they are installed extremely rarely on modern cars.

magnetoresistive

The work is based on the property of ferromagnetic materials to change electrical resistance when exposed to a constant magnetic field.

The part of the sensor that controls changes is made of two or four layers of iron-nickel plates with conductors deposited on them. Part of the element is installed in an integrated circuit that reads changes in resistance and forms a control signal.

The impulse rotor, which is a magnetized plastic ring in places, is rigidly fixed to the wheel hub. During operation, the magnetized sections of the rotor change the medium in the plates of the sensitive element, which is fixed by the circuit. At its output, pulse digital signals are generated that enter the control unit.

This type of device controls the speed, the course of rotation of the wheels and the moment of their complete stop.

Magnetoresistive sensors record changes in the rotation of vehicle wheels with great accuracy, increasing the efficiency of safety systems.

Based on Hall element

This type of ABS sensor operates based on the Hall effect. In a flat conductor placed in a magnetic field, a transverse potential difference is formed.

Hall effect - the appearance of a transverse potential difference when a conductor with direct current is placed in a magnetic field

This conductor is a square-shaped metal plate placed in a microcircuit that includes a Hall integrated circuit and a control electronic system.The sensor is located on the opposite side of the pulse rotor and has the form of a metal wheel with teeth or a plastic ring, magnetized in places, rigidly fixed to the wheel hub.

The Hall circuit continuously produces signal bursts of a certain frequency. At rest, the signal frequency is reduced to a minimum or dies out completely. During movement, magnetized areas or rotor teeth passing by the sensing element cause changes in the current in the sensor, which are recorded by the tracking circuit. Based on the received data, an output signal is generated and sent to the control unit.

Sensors of this type measure speed from the beginning of the vehicle’s movement and are distinguished by the accuracy of measurements and the reliability of their functions.

Causes and symptoms of malfunctions

In new generation cars, when the ignition is turned on, automatic self-diagnosis of the anti-lock braking system occurs, during which the performance of all its elements is assessed.

Signs	Possible reasons
Self-diagnosis shows an error. ABS is disabled.	Incorrect operation of the control unit. Broken wire from the sensor to the control unit.
Diagnostics does not detect errors. ABS is disabled.	Violation of the integrity of the wiring from the control unit to the sensor (break, short circuit, oxidation).
Self-diagnosis gives an error. ABS works without turning off.	Broken wire of one of the sensors.
ABS does not turn on.	Break in the power supply wire of the control unit. Chips and fractures of the impulse ring. Large play on a worn hub bearing.

In addition to the display of indicator lights on the dashboard, there are the following signs of a malfunction of the ABS system:

When applying pressure to the brake pedal, there is no reverse knocking or vibration of the pedal;
During emergency braking, all wheels are blocked;
The speedometer needle shows a speed less than the actual speed or does not move at all;
If more than two gauges fail, the parking brake indicator on the dashboard lights up.

In the event of a malfunction of the anti-lock braking system, a warning lamp lights up on the instrument panel

The reasons for the ineffective operation of the ABS may be:

Failure of one or more speed sensors;
Damage to sensor wiring, which results in unstable signal transmission to the control module;
A voltage drop at the battery terminals below 10.5 V disables the ABS system.

How to check the ABS sensor

You can monitor the serviceability of the speed sensor by contacting a car service specialist, or by yourself:

Without special devices;
Multimeter;
An oscilloscope.

Tester (multimeter)

In addition to the measuring device, you will need a description of the functionality of this model.Sequence of work performed:

The car is placed on a platform with a smooth, uniform surface, its position is fixed.
The wheel is dismantled for free access to the sensor.
The plug used for connection is disconnected from the general wiring and cleaned of dirt. The rear wheel connectors are located in the rear compartment. To ensure unobstructed access to them, you need to remove the rear seat cushion and move the carpet with soundproofing mats.
Conduct a visual inspection of the connecting wires for abrasions, breaks and damage to the insulation.
The multimeter is set to ohmmeter mode.
The sensor contacts are connected to the probes of the device and the resistance is measured. The standard readings can be found in the instructions. If there is no reference book, then readings from 0.5 to 2 kOhm are taken as the norm.
The wiring harness must be checked to exclude the possibility of a short circuit.
To confirm the functionality of the sensor, spin the wheel and monitor the data from the device. The resistance reading changes as the rotation speed increases or decreases.
Switch the device to voltmeter mode.
When the wheel moves at a speed of 1 rpm, the voltage should be 0.25-0.5 V. As the rotation speed increases, the voltage should increase.
Observing the stages, check the remaining sensors.

It is important! The design and resistance values of the sensors on the front and rear axles are different.

A resistance of 0.5 to 2 kOhm at the ABS sensor terminals is considered optimal

Based on the measured resistance values, the performance of the sensors is determined:

The indicator is reduced compared to the norm - the sensor is faulty;
Resistance tends to or corresponds to zero - interturn short circuit in the induction coil;
Changing the resistance data when bending the wiring harness - damage to the wire cores;
The resistance tends to infinity - a wire break in the harness or induction coil of the sensor.

It is important! If, after checking the functions of all sensors, the resistance value of any of them differs significantly, this sensor is faulty.

Before checking the wiring for integrity, you need to find out the pinout of the control module plug. After that:

Open the connections between the sensors and the control unit;
According to the pinout, all wire harnesses ring in turn.

The device allows you to more accurately determine the performance of the ABS sensor. Using the signal change graph, the magnitude of the pulses and their amplitude are tested.Diagnostics are carried out on the car without removing the system:

Disconnect the device connector and clean it of dirt.
The oscilloscope is connected to the sensor via pins.
The hub is rotated at a speed of 2-3 rpm.
The signal change schedule is recorded.
Using the same scheme, check the sensor on the other side of the axle.

An oscilloscope gives the most complete picture of the operation of the anti-lock braking system sensor

The sensors are operational if:

The recorded signal oscillation amplitudes on the sensors of one axis are identical;
The graph curve is uniform, without visible deviations;
The amplitude height is stable and does not exceed 0.5 V.

Without devices

Correct operation of the sensor can be determined by the presence of a magnetic field. For this purpose, any object made of steel is applied to the sensor body. When the ignition is turned on, it should be attracted.

In addition, it is necessary to inspect the sensor housing for its integrity. There should be no abrasions, insulation breaks, or oxides on the wiring.The sensor connector must be clean and the contacts must not be oxidized.

It is important! Dirt and oxides on the plug contacts can cause signal transmission distortion.

Sensor repair

A failed passive ABS sensor can be repaired yourself. This requires perseverance and mastery of tools. If you doubt your own abilities, it is recommended to replace the faulty sensor with a new one.

Repairs are carried out in the following sequence:

The sensor is carefully removed from the hub. The soured fastening bolt is unscrewed, having previously been treated with WD40 liquid.
The protective body of the coil is sawed with a file, being careful not to damage the winding.
Remove the protective film from the winding with a knife.
The damaged wire is unwinded from the reel. The ferrite core is shaped like a thread spool.
For the new winding, you can use copper wire from RES-8 coils. The wire is wound so that it does not protrude beyond the dimensions of the core.
Measure the resistance of the new coil. It must match the parameter of a working sensor located on the other side of the axis. Reduce the value by unwinding several turns of wire from the spool. To increase the resistance, you will have to re-wind the wire of greater length. Secure the wire with adhesive tape or tape.
Wires, preferably multi-core, are soldered to the ends of the winding to connect the coil to the harness.
The coil is placed in the old housing. If it is damaged, then the coil is filled with epoxy resin, having previously positioned it in the center of the housing from the capacitor. It is necessary to fill the entire gap between the coil and the walls of the capacitor with glue so that air voids do not form. After the resin has hardened, the body is removed.
The sensor mount is fixed with epoxy resin. It is also used to treat cracks and voids that have arisen.
The body is brought to the required dimensions using a file and sandpaper.
The repaired sensor is installed in its original place. The gap between the tip and the gear rotor is set to 0.9-1.1 mm using spacers.

After installing the repaired sensor, the ABS system is diagnosed at different speeds. Sometimes the system spontaneously trips before stopping. In this case, the working gap of the sensor is corrected using gaskets or grinding of the core.

It is important! Faulty active speed sensors cannot be repaired and must be replaced with new ones.

Video: how to repair an ABS sensor

Wiring repair

The damaged section of the wiring can be replaced. For this:

Disconnect the wire plug from the control unit.
Draw or photograph a diagram of the location of the wiring fastening brackets with distance measurements.
Unscrew the fastening bolt and dismantle the sensor with wiring, having previously removed the mounting brackets from it.
Cut off the damaged section of the wire, taking into account the length available for soldering.
Remove protective covers and brackets from the cut cable.
Covers and fastenings are placed on the wire, pre-selected according to its outer diameter and cross-section, using a soap solution.
Solder the sensor and connecting plug to the ends of the new harness.
Insulate solder joints. The quality of the insulation determines the accuracy of the signals transmitted by the sensor and the service life of the repaired section of the wiring.
The sensor is installed in place, the wiring is positioned and secured according to the diagram.
Check the operation of the system in different speed modes.

The soldering area must be properly insulated to increase the accuracy of the transmitted signals

The safety of road users depends on the effectiveness of the anti-lock braking system. If desired, you can diagnose and repair ABS sensors yourself, without resorting to the services of a car service.

A lambda probe is an O2 concentration sensor (or, more simply, an oxygen sensor) that allows you to estimate the volume of unburned oxygen contained in the exhaust gases. These indicators are extremely important, since by maintaining certain proportions of fuel and air, the most efficient combustion of the air-fuel mixture occurs. The best ratio is 14.7 parts oxygen to 1 part gasoline. If this ratio is violated, the mixture will be lean or, conversely, enriched, which, in turn, will affect fuel consumption and engine power.

Although outwardly the oxygen sensor does not look like a “vital” part, it performs a very important function, therefore any malfunction of the lambda probe, the “symptoms” of which we will consider, must be corrected immediately.

Signs and causes of lambda probe malfunction

According to statistics, oxygen sensors fail gradually, so you can identify its malfunction if you pay attention to the following “symptoms” in time:

The idle speed began to drop or “float”.
The car jerks, and after starting the engine, popping noises uncharacteristic of the engine are heard.
The engine power has decreased and when you press the gas pedal there is a slow response.
The engine overheats greatly and fuel consumption has increased.
The smell in the exhaust pipe has changed (exhaust gases have become more toxic).

As a result of a failed sensor, the quality of the fuel mixture entering the combustion chamber deteriorates, which disrupts the smooth operation of the engine. There can be many reasons for this:

Incorrect operation of the filament circuit or reduced sensitivity of the sensor tip.
Low-quality fuel with a high content of iron, lead, oil decay particles and other harmful inclusions. All these substances stick to the platinum electrodes, causing the sensor to malfunction.
Problems with the lambda probe heating system. If the heating stops functioning as it should, the oxygen sensor will produce inaccurate data.
Overheating of the regulator housing. This happens if the ignition timing is set incorrectly.
Worn oil scraper rings. In this case, engine fluid enters the exhaust pipe, which affects the lambda probe.
If the engine is started repeatedly.
Using sealants (especially silicone) to install lambda probes.
The compression level in the engine cylinders is impaired. In this case, the combustible mixture burns unevenly.
Clogged engine petrol injectors.

If you notice that the lambda probe is not working, you should not ignore the symptoms, as otherwise you will cause yourself a lot of problems with your car. The fact is that most modern cars are equipped with an emergency locking unit, which can work at the most unfortunate moment. However, the impossibility of further movement is not the worst thing. If the sensor becomes depressurized, the injection system will fail and you will have to pay for expensive repairs to a more serious unit.

Checking the oxygen sensor

Typically, diagnostics of a lambda probe is carried out using a voltmeter and an ohmmeter or a multimeter, which replaces both of these testers at once. To check the filament coil of the regulator, you need to disconnect pins 3 and 4 of the connector from the block (usually these are brown and white wires) and connect the ends of the tester to their clamps. If the resistance of the spiral is at least 5 ohms, then this is a good sign.

Also, checking the lambda probe with a multimeter allows you to find out the sensitivity of the tip of the oxygen sensor. To find out the thermoelectric parameters of the element, you need to turn on and warm up the engine to 70-80 degrees. After that:

Raise the engine speed to 3000 and hold this value for 3 minutes to allow the sensor to warm up.
Connect the negative probe of the tester (signal wire) to the ground of the car, and the second one to the output of the lambda probe.
Check the tester readings, the data should vary from 0.2 to 1 V and update up to 10 times per second.
Press the accelerator pedal sharply and release it; if the multimeter shows a value of 1 V, and then sharply drops to zero, then the lambda probe is ok. If the data on the tester does not jump when you press and release the pedal, and the readings are about 0.4 - 0.5 V, this indicates the need to replace the sensor.

If there is no voltage at all, then most likely the cause of the malfunction lies in the wiring, so use a multimeter to test all the wires that go from the ignition switch to the relay.

Healthy! To more accurately clarify the sensitivity characteristics of the lambda probe, you will need professional equipment - an oscilloscope.

If your car is equipped with a “smart” on-board system, then pay attention to the “Check Engine” signal, which may display the following errors:

0130 - indicates that the sensor is giving an incorrect signal.
0131 - very weak sensor signal.
0133 - lambda responds slowly.
0134 - no response at all.
0135 - malfunction of the lambda heater.
0136 - grounding of the second sensor is shorted.
0137 - the second sensor produces a very low signal.
0138 - too high signal of the second lambda.
0140 - probe break.
1102 - it is impossible to read the indicators because the resistance of the element is too low or completely absent.

However, before you check the lambda probe oxygen sensor (a video of this process is presented below) using a special tester, pay attention to its appearance. If substances have stuck to it that prevent it from working properly, then it may be possible to limit yourself to repairing this element.

How to repair a lambda probe

Repairing a lambda probe with your own hands is quite simple; to do this, you need to determine in which particular unit the failure occurred.

If the problem is related to the circuit contacts, then first of all you need to find the break point and check whether the contacts have oxidized. The signal may, elementarily, not come from the control unit. Therefore, check the lambda power supply. If the element contacts have oxidized, they must be treated with WD40.

If a lot of carbon deposits have formed on the probe body, it may be necessary to clean all parts of the system. And here a natural question arises: how to rinse the lambda probe. The fact is that it is strictly prohibited to process platinum electrodes and ceramic rods with sandpaper. Therefore, it is necessary to use specialized products designed to dissolve rust.

To clean the sensor, follow these steps:

Remove the lambda probe after preheating its housing to 50 degrees.
Remove the protective cap.
Soak the sensor in phosphoric acid for 30 minutes (it will cope with even the most difficult deposits).
Rinse the lambda in water, dry it and install the element back. Don't forget to lubricate the sensor threads with a special agent to create a complete seal (but don't use silicone sealant).

Since the cost of sensors ranges from 1000 - 3000 rubles per element, it is quite reasonable to try to repair the lambda probe yourself (see video below), and only then proceed to install a new element.

In custody

Vehicle systems are very sensitive and require constant diagnostics and preventative maintenance. In order for lambda probes and other elements to work properly, do not skimp on good fuel, because most often it is low-quality gasoline that leads to the rapid failure of important working elements.

You can only measure the resistance and voltage and check the wiring with your own hands. Check the functionality of the abs sensor It’s best to naturally connect an oscilloscope and by turning the wheel we will see a sine wave (measurement of the frequency and level of oscillation of the pulses transmitted by the sensor), you can have a pointer gauge (we’ll see the deviation of the arrow), a digital gauge will show an increase in voltage.

This number will not work on new machines, there is no sector, the bearing is magnetized and the sensor is a hall sensor.

To check the serviceability, you can make a “probe” consisting of an ordinary resistance of 900 - 1200 with wires ending in separate pins that “fit” into the connector. - Turning the wheels in one direction or the other, alternately connect the “probe” to the connectors, turn on the ignition and look at the behavior of the ABS light on the instrument panel. If, when connecting the “probe” to one of the connectors, the light goes out, the malfunction lies in this sensor.

Now let's take a closer look at checking the sensor with a tester. In order to do this you need a multimeter (tester). We check the resistance, it is different on different cars (1.2–1.8 kOhm), in general, all sensors should have approximately the same value. At the same time, you move the wires to the sensor in those places where they most often bend (between the body and the hub), the multimeter readings should not change, otherwise there is a break in the wiring. If the test described above passes, then switch the multimeter to voltage measurement mode, spin the wheel to 50 rpm and measure the voltage produced by the sensor. The voltage value is somewhere around 2V (the same on all sensors).

Thus, if the resistance is normal, the sensor is alive. But remember that with improvised means you can only check the resistance and voltage of the sensor. But to make sure that it works, you need to at least connect the VAG-COM, since in addition to the serviceability of the wiring and winding of the sensor, there is a problem with adjusting the gap (reading angle), which is diagnosed by the VAG-COM.

The use of an ABS sensor is associated with its induction properties (the sensor itself is an induction coil and a toothed ring). Due to these properties, the sensor can read pulses, transmitting them to the control unit. The control unit is responsible for the proper functioning of the hydraulics, and, receiving information from the sensor, regulates the oil pressure in the brake system. The ABS sensor, like other sensors in the car, may one day fail and the ABS sensor will need to be checked - this is a normal procedure that should be performed periodically.

The most common problem that occurs with the ABS sensor is a disruption in the circuit connecting the sensor to the control unit, as well as a breakdown of the sensor - these problems begin to distort the information received and transmit false data to the control unit.

A violation of the anti-lock system is detected while driving, as well as by the ABS light on the dashboard. The exact cause of the failure can only be determined after a thorough diagnosis.

The driver's first actions when the ABS light is on

Of course, a lit indicator light forces you to check the ABS sensor first. This can be done without going to a car service center. At the same time, for a correct check, the car owner will need a multimeter, an operating manual for the car, and wiring with PIN connectors. Yes, you can’t do without an extra pair of hands either.

How to check resistance

The multimeter operates in ohmmeter mode

Using a jack or lift, raise the car;
We dismantle the wheel (if, in your car model, it is an obstacle to the sensor);
We tighten the screw that fixes the sensor (it is located behind the hub);
We dismantle the casing protecting the ABS control unit, and then disconnect all connectors going to the controllers;
We include wiring with PIN connectors in the circuit, connecting them to the multimeter and to the sensor;
We measure the resistance, checking the standard data from the instruction manual;
We check the wiring to eliminate the possibility of a short circuit.

Using the help of a partner, you need to manually turn the wheel several times, recording the resistance indicators. When the rotation speed changes, the instrument readings should also change.

For a working ABS sensor, the multimeter will show the following indicators:

For the sensor-leg circuit: 5-26 Ohm;
For the sensor-ground circuit (circuit insulation check): at least 20,000 Ohms.

How to check voltage

The multimeter operates in voltmeter mode

We lift the car on a jack, hanging its wheels;
We connect the PIN connectors of the pre-prepared wiring to the contact of the multimeter;
We begin to rotate the wheel, trying to maintain the rotation speed at 1 revolution per second;

During normal operation of the sensor, the voltmeter readings will range from 0.25 Volts to 1.2 Volts. Please note that increasing the wheel speed will lead to an increase in the readings of the device.

Additional diagnostic options

You can also check the ABS sensor using an oscilloscope, which measures the amplitude and resistance values. However, an oscilloscope is very expensive, and it is much more difficult to use than a multimeter.

Another way to understand what exactly is broken when the ABS light is on is to decipher the information that the anti-lock braking system on new cars represents. As soon as such a system is activated, it displays coded errors on the car’s on-board computer screen. It is not difficult to decipher such errors; just study the machine’s operating manual, or find information on the error code on the Internet.

Attention! When checking the ABS sensor and connecting the multimeter wires to it, you need to observe the polarity. This is written in detail in the vehicle's Operation Manual: in particular, the color markers of the wires are described there and all connecting connectors are indicated.

Only after thoroughly checking the operation of the ABS sensor can you begin to repair or replace it. Repair means soldering damaged ABS sensor wiring and protecting the wire connections with a layer of electrical tape.

Video: Checking the ABS sensor

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A modern car is now equipped with a variety of so-called active safety systems, the list of which is growing every year. These include a system to prevent wheel locking during braking - ABS (Anti-lock braking system).

ABS is one of the very first safety systems that began to be used on a car, and it is now found on almost all cars, from budget categories to premium ones.

Let's briefly consider the purpose of ABS - this system is needed so that the wheels do not lock during braking, but continue to rotate, albeit at a slower rate.

Thanks to this, the grip of the wheel on the road surface is not lost and the likelihood of the car skidding is completely eliminated, the car remains fully controlled by the driver.

ABS has been used in vehicles for a long time and has proven its effectiveness more than once.

This system works simply. There is an electronic unit that controls the deceleration rate of each wheel. And if one of them stops faster than others, the block reduces the force of fluid pressure in the brake caliper on this particular wheel, that is, the brake mechanism begins to act less.

What is the ABS sensor for?

It is stated above that the ABS unit, popularly called the “brains” of the braking system, controls the speed of rotation of the wheels, so the design of this system could not be done without sensors.

They are the “sense organs” of this system and based on their readings the ABS functions.

The first anti-lock braking system used only one sensor, which was installed in the axle of rear-wheel drive cars.

But as ABS has improved, their number has increased; modern cars already use 4 sensors. This allows the system to monitor the rotation speed of each wheel individually.

Types of sensors

There are three types of such elements, differing in their operating principle. The most common passive sensors are induction type.

The essence of their work comes down to a change in voltage due to the influence of a magnetic field. Their main disadvantage is the inability to determine the speed of rotation of the wheel at very low speeds.

The remaining two types are active.

One of them is magnetoresistive (rare). The principle of its operation is based on the magnetoresistive effect - the property of a semiconductor to change the trajectory of electrons when exposed to a magnetic field.

The second type of active sensor uses the Hall effect, in which electrons on a semiconductor wafer move to its edges when the magnetic field changes.

Sensor Features

There are several significant differences between passive and active types. They are called passive because they do not require voltage to operate; such a sensor itself generates electrical impulses, to which the electronic unit reacts. Active elements require voltage to be applied to them.

Passive elements are very simple in design and are very reliable. That's why they are so common, despite their shortcomings.

Active types of sensors use microcircuits in the design, which complicates the element and makes it more vulnerable. But they are highly accurate and do their job even at low speeds.

Since all types of sensors operate under the influence of a magnetic field, it alone is not enough in the design; another element is needed to which it would react.

The induction (passive) type uses a ferromagnetic alloy pulse gear ring mounted on the drive hub or shaft, as well as on the steering axle. Previously, it could also be mounted on the bevel gears of the main drive.

In active types, a magnetic pulse ring is used. In the case of a magnetoresistive sensor, this ring is divided into alternating sectors with permanent magnets of different polarities.

But the Hall sensor uses a regular magnetic ring, without any sectors, integrated into the wheel bearing.

Inductive type element design

Since inductive sensors are the most common, their design will be considered in the future.

Such a sensor consists of an inductive coil, inside of which a magnetic core is placed. It is installed next to the toothed impulse ring, but so that there is a certain gap between them.

When the wheel rotates, the ring teeth pass through the magnetic field created by the core, which affects the magnetic flux, causing the alternating voltage value in the coil winding to change.

As a result, the speed of rotation of the wheel, and with it the pulse ring, affects the frequency and amplitude of oscillations of the output voltage on the coil. These parameters are fed to the “brains”, as a result of which they estimate the speed of deceleration of the wheel.

Problems with at least one of the ABS sensors can lead to a complete shutdown of the system. And although the braking system on the car will work, you can forget about the braking efficiency and safety that ABS provided.

Causes of sensor malfunction

The induction sensor is characterized by its simple design and high reliability; malfunctions with it occur very rarely. The problem most often lies in the wiring through which signals are sent to the control unit.

Since the sensors and their wiring are located directly next to the wheels, over time the circuit may break or short out. Often, sensor failures occur due to oxidation of the contacts.

Due to the fact that after turning on the ignition on a car, ABS always undergoes self-diagnosis, during which the condition of all elements of the system is assessed, it is quite simple to identify problems with the sensors; if they occur, the warning light will constantly light up on the dashboard.

In total, there are 4 types of system behavior when a malfunction is detected:

Self-diagnosis detects an error and ABS is disabled. This may be a sign of an error in the control unit, or a break in the wiring coming from the sensor;
The system undergoes diagnostics, during which no problems are detected, but after this the ABS is turned off. This result usually results from problems with the wiring going to the sensors (oxidation, open circuit, short circuit, etc.);
Self-diagnosis detects an error, but the system does not turn off and continues to operate. This usually indicates a break in the wiring on one of the sensors;
ABS does not turn on. This can happen due to a broken wiring, or because the impulse ring is damaged, chipped or broken. This result can also be produced by a heavily worn hub bearing, which is why there is significant play in it.

Since malfunction of ABS often occurs due to wiring, it is quite simple to identify a faulty element and all you need is a multimeter.

Of course, it is better to check using an oscilloscope, since such a device makes it possible to visually assess the amplitude and frequency of voltage fluctuations in the sensor, but not everyone has one.

Check on Ford Focus 2

First, let's look at how the test is carried out on a Ford Focus 2. This car uses a Hall effect sensor and is located in the upper part of the wheel hub. It is easy to detect - just remove the wheel, unscrew and move the caliper to the side, and also remove the brake disc.

Before starting the inspection, be sure to check the tire pressure. It must be the same in all wheels, otherwise the pressure difference may affect the performance of the system.

To check the sensor on Focus 2, for ease of access, you should jack up and remove the wheel from the side being tested.

At the first stage, we check the resistance. To do this, switch the multimeter to ohmmeter mode and connect its probes to the terminals in the block.

On Focus 2, the sensor resistance when measured should be in the region of 1.3-1.4 kOhm.

But there is one nuance that is important to consider. During measurements, you should knead the wire, especially at bends.

The fact is that at the point where the wire is broken, the copper conductors can come into contact, and therefore the sensor can show normal resistance. And during crumpling and bending, contact is broken.

If the readings do not match, a measurement should be taken at the input of the wires to the sensor. This will reveal whether the problem lies in the sensor itself, or just in the wires.

If, when checking the resistance near the element, a discrepancy in resistance remains, then the sensor must be replaced.

In some cases, the cause of the problems lies in contamination of the semiconductor platinum of the Hall element. Therefore, you should remove the sensor itself and clean it.

In addition to the sensor wiring, you should also check the entire circuit for damage. To do this, you need to disconnect the wire block from the control unit.

Then we find out from the technical documentation for the car which terminals on the block correspond to which sensor, after which we connect a multimeter to the necessary connectors and measure the resistance.

If it does not meet the required parameters, you should look for a break in the area from the control unit to the sensor connection block.

Faults such as breaks or short circuits can be treated by replacing the wires. But if the element itself malfunctions, it is replaced.

Diagnostic features for BMW E39

Diagnostics are carried out using the same methods as for Focus 2. That is, the resistance of the sensor, its wiring, as well as the circuit from the control unit are checked.

Since this car uses an induction type element, it is additionally possible to measure the output voltage.

To do this, switch the multimeter to voltmeter mode and connect it to the sensor wiring connectors.

Design nuances of Lada "Priora", "Kalina"

Now let’s figure out a little how to diagnose and replace Lada cars of the Priora and Kalina models. These cars were taken as an example because they use drum brakes at the rear, and above we looked at how work is carried out with sensors that work with disc mechanisms.

Checking the sensors on Kalina or Priora is completely identical to those described. But this sensor still needs to be found. The element is installed in the rear wall of the hub, and the impulse ring is located inside the mechanism, under the drum.

Therefore, in order to assess its condition, you will have to remove the drum from the car, and immediately under it you will see the ring, as well as the protruding part of the sensor, which passes through the technological hole in the brake pad.

That is, by checking the condition of the ring, you can immediately look at and clean the sensor itself from dirt. And then we measure the resistance of the sensor and the entire circuit up to the “brains”.