Hydraulic Control Assembly - Antilock Brakes: Description and Operation

ABS Control Module Input/Output Signal Description

ABS Hydraulic Unit/Control Module Assembly Description
ABS control module is a component of ABS hydraulic unit/control module assembly and has the following functions.

Self-Diagnosis Function
ABS control module diagnoses conditions of the system component parts (whether or not there is any abnormality) all the time and indicates the results (warning of abnormality occurrence and DTC) through the ABS warning lamp as described.
1. When ignition switch is turned ON, ABS warning lamp lights for 2 seconds to check its bulb and circuit.
2. When no abnormality has been detected (the system is in good condition), ABS warning lamp turns OFF after 2 seconds.





3. When an abnormality in the system is detected, ABS warning lamp lights and the area where that abnormality lies is stored in the memory of EEPROM in ABS control module.








4. When Diag. switch terminal (2) of diagnosis connector (1) (monitor connector) is grounded, the abnormal area is output as DTC. It is indicated by flashing of ABS warning lamp.
5. For procedure to clear all DTC's, refer to "DTC Clearance.
Also ABS control module turns ON EBD warning lamp (brake warning lamp) depending on the trouble that detected by the module and EBD warning lamp does not indicate DTC as well as ABS warning lamp.

Fail-Safe Function
When an abnormality occurs (an abnormal DTC is detected), ABS control module turns OFF the fail-safe relay which supplies power to ABS hydraulic unit. Thus, with ABS not operating, brakes function just like the brake system of the vehicle without ABS.

Tires and ABS
Spare Tire
Using the compact spare tire supplied with the vehicle will not affect the operation of the ABS. The ABS control module can compensate for this smaller tire. However, increased stopping distance may occur due to reduced tread depth.

Replacement Tires
Tire size is important for proper performance of the ABS. Replacement tires should be the same size, load range and construction as the original tires. Replace tires in axle sets and only with tires of the same Tire Performance Criteria (TPC) specification number. Use of any other size or type may seriously affect the ABS operation. For more information on original equipment and replacement tires, refer to "Replacement Tires Description:".