Anti-lock brake system (ABS control unit)
P-37
Description of ABS control unit during the maintenance process
The ABS control unit is composed of the electric and mechanical parts. When the faults are diagnosed, it is
necessary to divide those faults into the electric system and hydraulic pressure unit.
1. Electric system fault
a. The ABS control unit modular has the fault diagnostic function. According to such function, the warning
light of ABS control unit will lighten up when there is a failure occurred in the electric system. At the
meantime, the previous and current faults can be recorded on the ABS control unit modular. This fault
diagnostic function is able to detect the faults not yet shown up during the regular inspection. After the
TBS terminal on the DLC is short-circuited with the grounding end, or connected with the SST, enabling
the ignition switch to turn in the ON position. In 5s, the saved fault codes will show up according to the
priority of presence. To find out the fault origin of ABS control unit, refer to the table of fault diagnostics.
If there has been the presence of some certain fault, it is now a normal case, and came about due to the
temporarily bad contact of harness. The control modular of ABS control unit remains in normal
communication. When tracing the reasons of faults, be careful not to damage the sensor elements.
b. After the repair, delete the fault codes saved in the modular in the ABS control unit. At the meantime, if
the parts associated with the ABC control unit have been replaced, confirm that the fault codes do not
exist any further after the replacement.
c. After the wheel speed sensor of ABS control unit repaired or the ABS control unit replaced, even if the
ignition switch were turned in the ON position, the warning light of ABS control unit may be not go off.
At this moment, please drive the vehicle at the speed more than 15km/h, allowing the ABS control unit
system to carry out a dynamically self-check. Assure that the ABS control unit light has gone off and
then delete the fault codes.
d. If the relevant plugs of ABS control unit disconnected and the ignition switch turned in the ON position
during the repair, the control modular of ABS control unit will take it as an error and record it as a fault.
e. To protect the control modular of ABS control unit, prior to connect or disconnect the control modular
plug of ABS control unit, the ignition switch has to be turned in the OFF position. In order to protect the
terminal, the SST must be used when the tester terminal is connected with the control modular plug of
ABS control unit.
2. Faults in the hydraulic pressure unit
a. The faults of hydraulic pressure unit are similar wit those in the conventional brake system. it 必须 must
be determined whether the fault exists inside the component of ABS control unit or in the conventional
brake system;
b. The precision parts are contained in the hydraulic pressure component of ABS control unit. If foreign
materials are mixed inside, it may result in failures and hinder the ABS control unit from the operation.
As it is very difficult to localize the fault position, cares must be taken to avoid foreign substance from
ingress into the hydraulic pressure unit of ABS control unit, when the ABS control unit is under
maintenance (if the brake fluid is replaced or the pipeline removed).
Index of diagnostics
1. Sometimes, cases may exist, where there are no records of fault codes in the modular of ABS control unit
control while both the warning light and indicator light are lit.
In the following table are listed the faults with such phenomena and the fault symptoms, where, indicator
light doesn’t lighten up.
2. Confirm the fault and carry out the operation of fault diagnostics according to the suitable S/N.
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