Actron ABS BrakeScan CP9449 User Manual download pdf (Page 9)

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Section 2 – Getting Started

Introduction

ABS BrakeScan is the first tool designed

for Do-It-Yourselfers to access the

ABS diagnostic information. The Tool retrieves codes from the ABS system and

provides the definition of each code to help pinpoint the problem areas within

the Antilock Brake System that may have caused the ABS light to turn on.

The Tool was developed by experts in the automotive service industry to access

the information stored in the ABS module.

All information, illustrations and specifications contained in this manual are

based on the latest information available from industry sources at the time of

publication. No warranty (expressed or implied) can be made for its accuracy

or completeness, nor is any responsibility assumed by the manufacturer or

anyone connected with it for loss or damages suffered through reliance on any

information contained in this manual or misuse of accompanying product. The

manufacturer reserves the right to make changes at any time to this manual or

accompanying product without obligation to notify any person or organization

of such changes.

ABS Overview

Anti-Lock Brake Systems (ABS) began bei

ng used on vehicles in the

mid-1980's. The mechanical components of the hydraulic-brake system

(master cylinder, shoes, pads, wheel cylinders, calipers, rotors, drums, and

assorted hardware) work the same as they did before ABS. What has changed,

however, is the addition of an ABS computer module, wheel speed sensors, and

a hydraulic control unit consisting of solenoid valves.

How ABS works

When th

e brake pedal is pressed with normal force, the vehicle decelerates. If,

during deceleration, the ABS computer detects wheels going at different

speeds (wheels slipping) from data provided by the wheel speed sensors, then

the vehicle enters antilock mode. During antilock mode, the ABS computer will

control brake fluid hydraulic pressure delivered to the wheels. The brake fluid

hydraulic pressure will be equal to or less than the value delivered by the master

cylinder. By controlling pressure to the wheels, the ABS computer can prevent

one wheel from locking up while others keep turning. It can also prevent wheels

from turning at different rates, so the vehicle should stop in a straight line.

ABS Configurations

ABS has had three different configurations for distribution of wheel speed

sensors and hydraulic lines from the hydraulic control unit since its conception:

• The earliest ABS configuration used one wheel speed sensor that monitor

the speed of both rear wheels. If the rear wheels would lock up, the ABS

computer would pulse a solenoid in the hydraulic control unit, which would

then change the brake fluid hydraulic pressure applied to the rear wheels.

• The next evolution in ABS added wheel speed sensors to both front

wheels, while still having a single wheel speed sensor in the rear to monitor

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Actron ABS BrakeScan CP9449 User Manual Page 9

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