Technical information

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Technician Guidelines for Antilock Braking Systems

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Vehicle Power The voltage and current delivered to various electrical and/or

electronic devices on a vehicle. Typical vehicle power in North

America is 9.0-16.0 volts direct current. European vehicles

typically operate from 18.0-32.0 VDC. TMC Recommended

Practice 137 establishes a voluntary standard that tractors

should deliver a minimum power level of 12.5 volts at 10 amps

load. TMC Recommended Practice 141 establishes a voluntary

standard that at least 9.5 volts (which includes a 1.0-volt safety

margin) must be available at the trailer ABS ECU to ensure

proper operation.

Warning Lamp See Malfunction Indicator Lamp

Wheel-by-Wheel Control A type of ABS control in which each wheel is controlled

individually.

Wheel Slip The difference between vehicle speed and wheel speed, ex-

pressed as a percentage. The formula is: Wheel Slip =

(100)(Vehicle Speed-Wheel Speed)/(Vehicle Speed).

Wheel Speed The measured velocity of an individual (sensed) wheel which is

derived by the ABS ECU. Wheel speed may differ from vehicle

speed during wheel slip. See Wheel Slip.

Wheel Speed Sensor Pickup A magnetic pickup-type sensor—coupled with an exciter or

tooth wheel—that produces a signal to indicate wheel speed to

the ECU. A permanent magnet and passing metal teeth com-

bine to produce an electrical signal with a frequency propor-

tional to the wheel speed. The teeth alter the magnetic field

produced by the sensor. The changing magnetic field produces

an AC voltage in pickup coil within the sensor.