Anti-locking wheels
service The anti-locking wheels service is divided into maintenance and repair operations. The maintenance work of the system is carried out periodically, which is about checking, cleaning and adjusting the parts of the system. As for repair operations, they are detected and examined to determine the cause of the malfunction and to replace or repair the damaged part.
Maintenance of the system to prevent the closure of the wheels
to prevent the closure of the wheels system needs very little maintenance. When lifting the car on the crane, the condition of the toothed ring and the wheel speed sensor is checked, whether there is damage or the presence of obstructions from the road (obstructions, whether from the car (lubricant) or from the road), they must be removed. Check the condition of the wires for signs of damage or lack of installation. The antilock system parts and components must be inspected at every maintenance.
Checking the brake fluid level of the ABS master cylinder
The fluid level should be checked periodically, as in a conventional system. Confirm the manufacturer’s requirements for liquid level before adding a volume to the liquid. The brake fluid level mark in the ABS for most vehicles is inside the tank, see Figure (1).
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| Figure 1: Checking the brake fluid level |
Most auto manufacturers recommend that the brake fluid system should be disposed of and replaced with new fluid, periodically to ensure that the fluid does not become contaminated and affects the components of the system. Review the manufacturer’s recommendations and follow the steps provided to perform the liquid ejection process.
| Warning: * On some vehicles, the pressure in the system circuit must be lowered before a fluid level check is performed. * When adding brake fluid to vehicles equipped with the system: Do not use brake fluid (DOT 5) as this will damage the interlocks and system parts. A new can of liquid must be used, or it has not been opened for more than 48 hours, in order to ensure that it is not contaminated to preserve the parts of the system. |
Diagnostics and repair of ABS system malfunctions
To determine the causes of malfunctions of the ABS system, logical steps must be followed to examine and diagnose faults in order to reach the actual causes of malfunctions in the least time and at the lowest cost. Here are the steps that can be followed to diagnose the malfunction.
* Note the performance of the warning lamp.
* General inspection of brake system parts and components.
* Obtaining problem information from the driver of the vehicle.
* Vehicle test on the road.
* Initial inspection of the vehicle equipped with the anti-lock wheel system.
* Check the performance of the anti-lock brake system.
The operation of the warning lamps for the brake system
The warning lamp for the conventional brake system (red):
This lamp lights up when the ignition switch is turned on and the starter is running, and then turns off after that. It also lights up to warn of a problem in the conventional brake system, as follows:
o Low brake fluid level.
o Low pressure problem (liquid leakage) in one of the car’s hydraulic circuits (double or dual circuit).
o If the hold brake is used.
The ABS warning lamp (yellow)
This lamp lights up when the ignition switch is started and turns off after a short period (the ABS is checking the system. other. It lights up if there is a malfunction in the anti-lock brake system.
| CAUTION * When the brake warning light is illuminated, you must check the conventional brake system first. Even if the ABS lamp is illuminated. There is no exception to this rule. * Do not assume there is a problem with the antilock system before you have checked the parts of the conventional system first. * Most of the hydraulic parts and some parts of the wheel brakes (circuit, disc, bushings, shoes, etc.) are different from those in the conventional brake system. * Most integrated units and a few separate units of the ABS operate at high pressures up to 2000 psi (13790 kPa). Be sure to release the pressure in the hydraulic system before carrying out any work, even if the detection is at the fluid level. * Always remember to check the simple things first like brake fluid level or fuse. Oftentimes, the technician takes a long time trying to find a fault with the antilock system and the problem is a fuse. * Anti-locking wheels parts and accessories are very expensive. Don’t change parts randomly in an attempt to get rid of the problem. You must accurately diagnose the malfunctions. * You must use logic, and use the right steps to reach the solution to the problem. |
Check by looking at the components of the brake system
§ Brake fluid level Check the condition and level of fluid in the reservoir.
§ Brake fluid leakage Check the condition of pipelines, connections and interlocking work.
§ Fuse condition Check the condition of all system fuses.
§ Wires and connections Check the condition of the wires, especially the wires of the speed sensor.
§ Speed sensor The condition and cleanliness of the speed sensor ring teeth.
§ Parts of the conventional brake system, the case of the disc, circuit, bushings, saddle, shoes…etc.
§ The installation brake is set and not loaded.
The calf pomegranate has no defects or problems and it is fine.
§ The wheels and tires are the correct size, proper air pressure and good condition of the tires.
Initial inspection of a vehicle equipped with an ABS system
Before starting to diagnose the malfunction as a malfunction of the ABS system, an initial inspection of the vehicle must be carried out.
q Check tire dimensions:
If there is a problem with the vehicle’s speed, check the vehicle to ensure the size of the tires fitted to the vehicle. An incompatibility in the tire size will lead to a different speed of the tires, causing problems with the system control unit.
q Check brake fluid level:
A low level of brake fluid may cause the warning lamp to illuminate, and the antilock system warning lamp can also illuminate. Low brake fluid level could be due to excessive lining or disc wear or fluid leakage. Check all brake connections.
q Servo Check (for vehicles with ABS):
Servo problems may make the pedal difficult and slow. Check the vacuum
servo vacuum and the fluid level on the hydraulic servo.
q Check wheel brake condition:
Wear of the friction linings, disc or circuit, or failure to adjust shoe clearance may cause the hydraulic system to pump more fluid which affects the pressure increase rate in conventional brakes which will affect the performance of the antilock system. Irregular wear of the disc or lack of rotation of the circuit causes uneven operation of the hydraulic system, which also affects the pressure condition of the system.
q Checking the battery charge status:
The condition of overcharging and low charging (charging voltage) will result in poor performance of the electronic controller. Check the charging voltage and the motor at no-load speed. During the check, make sure that the electrical circuits in the car that need to draw a high current are not working. The voltage is within (13 volts) at no-load speed and (14.5 volts) at full throttle opening. In most cases, the ABS does not operate at voltages less than (9.5-10V) or more than (14.5-15V). In the event that the voltage is low, check the tension and condition of the generator belt. In the case of high voltage, check the ground connection of the voltage regulator or an internal malfunction.
q Check the condition of the wires and electrical connections:
Check the condition of the wire connection and the proper path for it, as well as the insulation condition of the wires. The anti-lock wheel system is very sensitive to the influence of electromagnetic fields and radio frequency waves, which interfere with the system.
Source of interference and interference with system performance:
o Improper path of system wiring.
o Cut or ground the secondary circuit wires of the ignition system.
o Malfunction of the charger diode.
o Wrong installation of some electrical devices in the car.
Improper routing of the speed sensor wires, which may cross paths with other wires (even if they carry a weak current) may lead to problems with some antilock systems.
Obtaining information from the driver of a vehicle
As a start in diagnosing malfunctions in the anti-locking wheel system, the vehicle driver can be asked about the type of problem with the vehicle. The rate at which the problem occurs (intermittently or continuously) and is observed on the vehicle’s performance. The data can be written down for reference when the repair procedure is completed.
Take a car test on the road
Note the brake warning light, if it is still on after the engine is started, do not test the vehicle on the road and check the conventional brake system. If one of the lights stays lit for a long time after the engine has been running, there is a defect or leak in either the hydraulic circuit, the pump, or the pressure manifold.
If the warning lights go out, and before you start driving the car, check the condition of the brake pedal.
In the event that the conventional brake system is working, you can now test the car on the road. Test the car in a safe place away from the path of cars or parked cars. When braking hard enough to make the ABS system work, the vehicle must stop without swerving or locking up the wheels. And he noticed the presence of pulsations in the pedal when the anti-lock system system was working (its strength varies from one system to another). If you do not feel the pedal pulsing when using strong braking, this indicates that the antilock system may not work. During the operation of the anti-lock system, an intermittent beeping sound is heard (the sound of the wheel before locking).
Methods for diagnosing malfunctions of the anti-locking wheel system
When a problem occurs in the anti-locking wheel system in most cars, the electronic unit stores information about the problems in the form of a malfunction or problem code to obtain or extract that information by using a special connection (malfunction detection plug) in the car And connected with the electronic unit.
Using the ABS Code Indicator on the dashboard A
common way to obtain the malfunction code is by grounding one end of the infotainment connector. When the terminal is connected to ground, the warning lamp (yellow) on the dashboard begins to flash, and through these flashes, the type of malfunction can be determined. If there are more than one fault, the fault with the lowest number flashes first. Refers to the fault code manifest list to determine the type of fault present.
Using a diagnostic device
To use a fault code to extract the fault code.
§ Make sure that you use the correct information card with the fault diagnosis device.
§ Ensure that the ignition switch is in the off position, then connect the device to the fault detection plug using the correct connectors.
§ The fault scanning device is connected to an electrical source in the car to operate it, through the battery or the lighter connection. In some devices, the device obtains the source of electricity for operation through the information connector connection.
§ The device will perform a self-test, then the device will ask you to enter the vehicle’s data. After entering the required data, the device will ask you to enter the system to be checked.
§ The key ignition mode on playback mode ( the ON ) for the holidays code. The device will ask you for your consent to get the fault code. When you agree, the device will display the fault number.
§ After obtaining the fault code, the faults can be recorded and then the device can scan the fault codes from the control unit.
Check the wheel speed sensor
if the fault code indicates a problem with the wheel speed sensor. You should start checking that sensor by looking before starting any other procedure. Check the sensor for the presence of plankton (grease, etc.) between the sensor and the teeth of the sprocket ring. Examine the sprocket teeth for possible broken tooth or tooth damage.
Checking the clearance between the toothed ring and the wheel speed sensor
Check the distance between the sensor and the ring (clearance) by means of a clearance measurement sensor (Filter). Spin the wheel and measure in several places on the circumference, the clearance should be as per the specifications and there should be no significant difference in the readings, Figure (2). In the absence of clearance distance data, measure the clearance of the remaining wheels and compare the clearance of this wheel to the remaining clearances.
If the clearance is adjustable, follow the manufacturer’s instructions and steps. When adjusting the clearance, use a sensor to measure the clearance, the iron plate will be attracted to the sensitive magnet.
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| Figure (2): Sensor clearance measurement |
Checking the electrical output of the wheel speed sensor An ohmmeter
can be used to measure the resistance of the sensor coil. Lift the sensor cable connection and connect the resistance scale between the sensor terminals, Figure (3). In the event that the resistance of the coil does not meet the specifications, the sensor must be changed, the resistance of the coil is within (1000 ohms). In the event that the resistance of the coil is infinite or zero ohms, it means that the sensor is damaged.
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| Figure (3): Measuring the resistance of the sensor coil and measuring the insulation of the sensor coil |
Replacing the wheel speed sensor The wheel
sensor is usually attached to the suspension link bolt and there are clips to hold the wires in place. After installing the new sensor, adjust the sensor clearance (if it is compressible) using a copper or plastic gauge plate. Figure (4) shows how to remove the sensor from the car.
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| Figure (4): Replacing the wheel speed sensor |
Wheel Speed Sensor Quick Check:
1. Lift the vehicle on the jack .
2. Turn the ignition switch on the operating mode ( the ON ) only ( the engine does not work)
3. Turn one of the wheels by hand (by boat speed sensor) as quickly as possible.
4. In this case, the warning lamp (yellow) of the anti-locking wheel system should illuminate the cylinder, this means that the electronic unit has detected that there is speed in one of the wheels, but not on all wheels (in this case it is necessary to make sure that the lamp is working).
5. Turn off the ignition switch to start the system again.
6. Repeat the previous steps for all wheels equipped with a speed sensor.
* In the event that one of the wheels when turning does not illuminate the warning lamp, this is an indication of problems with the speed sensor, check the resistance of the sensor, wires, and sprockets.
* In the event that the warning lamp lights up and does not go out when the ignition is switched off, this means that the problem is not with the speed sensor.
Summary
* The Anti-lock Wheel System prevents the wheels from locking up by controlling the brake fluid pump at a high speed.
* The electro-hydraulic unit operates through three stages of pressure stabilization, pressure reduction and pressure increase.
* The wheel speed sensor sends voltage pulses whose frequency is proportional to the speed of rotation of the wheel.
* In the event that one of the wheels has a lower angular velocity at a high rate or less than the rest of the wheels. The electronic unit sends a signal to the electro-hydraulic unit to control the hydraulic pressure of the respective wheel by means of electromagnetic valves.
* If the electronic control unit detects a malfunction in the anti-locking wheel system, it will turn off the system and illuminate a warning lamp that the system is not working in the car.
* Anti-lock brake system malfunction does not affect the performance of the conventional hydraulic brake system.
* Some control units store codes for system faults and can be extracted either by a fault diagnostic device or by a fault detection lamp.
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