9.2. System of anti-blocking of brakes (ABS) - the general information and codes of malfunctions

The scheme of an arrangement on the car of the ABS elements

When the vehicle is equipped with the brake system of usual type, sharp squeezing of a pedal of a foot brake leads to blocking of wheels. At the same time coupling of a protector with a paving is broken, and the car can start to skid, losing controllability. The system of anti-blocking of brakes (ABS) prevents premature blocking of wheels, continuously operating the speed of their rotation during braking due to modulations of pressure of hydraulic liquid in each of brake mechanisms.

ABS consists of two main subsystems: electric and hydraulic. Four sensors of speed of rotation of wheels, the sensor of acceleration (G-sensor), an electronic control unit (ECU) and a set of a connecting electrical wiring enter an electric part of system (see the illustration Scheme of an Arrangement on the car of the ABS elements). A hydraulic part includes pressure modulator, supports / wheel cylinders of brake mechanisms and lines of communication connecting components.

The principle of functioning of system is rather simple. Each of wheels is equipped with the individual RPM meter. The sensor consists of a rotor (a ring with the teeth which are evenly located on its perimeter) and a sensitive element in the form of the podmagnichenny coil. The sensitive element of the sensor fixes the moments of passing of rotor teeths by it and will transform the obtained information to the electric signals which are continuously transferred to the ABS control unit. By results of processing of the arriving signals of ECU obtains information on the relative speed of rotation of each of wheels. While all four wheels rotate with an identical frequency, ABS stays in a passive state. As soon as any of wheels begins to be blocked, the control unit fixes change of the entering signal and develops the command for operation of the modulator which is instantly dumping pressure of hydraulic liquid in the brake mechanism of the corresponding wheel. As soon as normal rotation of a wheel is restored, the processor stops functioning of the modulator. Let's notice that switchings of the modulator can happen to speed of one hundred times a second.

One more ABS element used on the Infiniti QX4 models is the sensor of acceleration (G-sensor). Normally closed reed G-sensor is installed under assembly of the central console in interior of the car (ahead of the lever of the parking brake) and serves for transfer on the module of management of ABS information on the overloads arising during dispersal or braking of the vehicle. The analysis of the arriving signals together with the data accepted from wheel sensors, and information on working parameters of the power unit allows the processor of the module to define reliability of coupling of protectors of wheels with a paving and to exercise control of functioning of the hydraulic modulator taking into account this factor.

Actually the scheme of functioning of ABS is much more difficult, than it can seem therefore authors of the present manual do not recommend to owners of cars to make attempts of independent performance of repair of system. In case of malfunctions it will be most reasonable to address specialists of car service.

At identification of any sort of violations of functioning the ABS control unit is exercised by transition of system to emergency operation by power off from the hydromodulator, at the same time the corresponding diagnostic code is brought in memory of system of self-diagnostics, and the brake system continues to work in the usual mode (without ABS).

ABS failure diagnostics

Preliminary checks

Before starting check of a condition of the ABS components, it is necessary to make sure during a trial trip that the manner of driving of the owner of the vehicle is not a cause of infringement.

Check the level of brake fluid. If level is normal, pass to the following stage of check, otherwise check a condition of brake shoes and explore the hydraulic highway of system on existence of signs of development of leaks. Rectify debugged, in case of need make replacement of blocks, or correct level by addition in the GTTs tank of the corresponding amount of hydraulic liquid of the required grade.

Estimate serviceability of functioning of the standard brake system (including checks of a condition of the vacuum amplifier and correctness of adjustments of brake mechanisms and the parking brake). Make necessary corrections.

Include ignition, and make sure of serviceability of operation of a control lamp of ABS (see the Head the Maintenance instruction). Start the engine — the control lamp of ABS has to go out. At refusals of a control lamp it is necessary to make reading of the codes of malfunctions brought in the processor memory (see below) — told treats as well cases of operation of a control lamp after dispersal of the car to the speed over 30 km/h and the movement in this mode within not less than 1 minute.

Reading of codes of malfunctions (DTC) of ABS

Reading of the DTC codes by means of a control lamp of ABS

At identification by the processor of malfunctions in system in an instrument guard lights up and remains to ABS included a control lamp. Diagnostics of malfunctions of anti-blocking system is among enough difficult procedures and authors of the present manual do not recommend to make it in house conditions. Nevertheless, it is possible to allocate a number of the elementary checks which can be quite successfully made by own forces of the owner of the car and allow to define qualitatively a cause of failure (see further).

Reading of the DTC codes is made by means of the special scanner connected to the 16-contact diagnostic socket located at the left under the car dashboard.

Alternatively codes can be schitana by means of a control lamp of ABS: by means of a wire crossing point ground the CONSALT socket plug No. 4. Without squeezing out a pedal of a foot brake, include ignition. About 3 seconds later the control lamp will begin to give flashing signals, highlighting the codes brought in the processor memory. The figure of tens of code is defined by quantity of the gleams of a lamp lasting 0.6 seconds divided among themselves by pauses of the same duration, the figure of units of a code is separated by a pause lasting 0.9 seconds. The figure of units of a code is defined by quantity of gleams of a lamp lasting 0.3 seconds. The moment of the beginning of reading is noted by delivery of a code 12 (one gleam, a pause, two gleams). Then again the pause after which the lamp begins to highlight the codes which are stored in memory of the control unit follows long (3.3 seconds).

At first the lamp always highlights a code of the beginning of reading (12), further there are DTC codes (to three in a row, starting with the last) (see the illustration Reading of the DTC Codes by means of a control lamp of ABS). Completion of process is confirmed by repeated highlighting of a code 12. If only the code 12 is highlighted, and the symptom of refusal takes place, the car should be driven away on car repair shop for performance of standard diagnostic checks according to the card of symptoms. The simplest malfunction can be the reason of entering of a code into the processor memory — first of all make the following checks:

The following is among the diagnostic checks of symptoms entering the card:

Too frequent operation of ABS

Test A

Inadequate reaction of a pedal of a foot brake to squeezing

Test B

Excessiveness of length of a brake way

Test C

ABS functioning refusal

Test D

Vibrations and noise of a pedal when braking

Test E

Refusal of operation of a control lamp of ABS at inclusion of ignition

Test F

Refusal of switching off of a control lamp of ABS after implementation of start of the engine

Test G

Excessive vibrations of the car at ABS operation

Test N

The ID card of codes of malfunctions of ABS is provided in Specifications.

Performance of any recovery repair should be charged to specialists of car service.

Cleaning of the processor memory of ABS

After elimination debugged system the processor memory it has to be cleared. Cleaning of memory can be made either by means of the scanner, or by double grounding of the plug No. 4 for 1 second during a 12.5-second interval — during the whole time of removal of codes the control lamp of ABS remains included, then has to go out.

In repeated attempt of reading the code 12 is highlighted even if all faults were rectified.

More detailed information on the skanerny reader is provided in the Head of the Feed and control system.