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 Electronic brake control systems integrate computer controls to prevent
wheel lock-up, shorten panic stop distances, help drivers maintain steering
control, and improve vehicle stability.
 Basic anti-lock brake systems control hydraulic pressure hold and release via
solenoid valves, but cannot function independently of the driver’s applied
brake pressure.
 Traction control systems minimize wheel slip by automatically applying
brake pressure to a slipping wheel’s brake unit and reducing engine output.
 Electronic stability control systems use steering wheel position sensors, yaw
sensors, and wheelspeed sensors to independently monitor vehicle stability
and apply brakes as necessary.
 Primary components of an anti-lock braking system are: ABS master
cylinder, electronic brake control module/electronic control unit, hydraulic
control unit/modulator, power booster, wheel speed sensor, and brake
switch.
 Braking force and wheel lock-up are affected by friction of road surface and
type, condition, and loading of each tire.
 Maximum traction occurs with 10–20% tire slip.
 Wheel speed sensors signal the EBCM, which sends current to the solenoid
valve, which then holds or releases hydraulic braking pressure.
 ABS master cylinders are integral (mainly in older vehicles) or nonintegral
with the HCU.
 Solenoid valves provide three operating conditions: apply, hold, and release.
 The hydraulic control unit executes the commands of the ABS control
module.
 Hydraulic control units differ by number of channels (one, two, three, or
four), number of solenoid valves (single or dual), and type of accumulator
(low or high pressure).
 Wheel speed sensors send electric signals to the EBCM to determine speed
and rate of deceleration for each wheel.
 Wheel sensor assemblies are comprised of a toothed tone wheel and a pickup
assembly, separated by an air gap.
 Types of wheel speed sensors are: variable reluctance, magneto-resistive,
and Hall effect.
 The EBCM is comprised of electronic circuitry, electronic data processor,
computer memory, and output drivers.
 The EBCM receives input signals from: the brake switch, ignition switch,
vehicle speed sensor, wheel speed sensors, and sometimes the battery.
 The ESC system includes a yaw sensor (directional rotation), steering angle
sensor (driver’s directional intent), and roll-rate sensor (rate and amount of
vehicle roll).
 Some TCS and ESC systems can be manually deactivated by the driver.
 EBCM systems can self-diagnose and store faults as diagnostic trouble codes
(DTCs) for technicians to retrieve.