Technical information

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Technician Guidelines for Antilock Braking Systems

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Failure Lamp An indicator lamp that indicates ABS operational status. See

Malfunction Indicator Lamp.

FMVSS Federal Motor Vehicle Safety Standard. FMVSS 121, “Air Brake

Systems,” is the regulation that applies to air brakes used on

commercial vehicles.

Four-Channel ABS A system that has four sensors and four modulators (4S/4M) or

six sensors and four modulators (6S/4M).

Full-Time Power This term refers to an ABS design in which a circuit connects

the tractor and trailer to supply constant electrical power for an

ABS. See Stop-lamp Power.

Ghost Sensing In-axle Speed Sensing Systems where one wheel/axle is sensed

and the differential gear is sensed. The ECU uses these two

inputs to calculate the speed of the unsensed wheel (i.e., the

ghost sensor). Ghost Sensed Speed = (2)(Average) - Individual.

In-Axle Sensor/Sensing The practice of locating wheel speed sensing devices inside the

drive axle housing of the ABS-equipped vehicle. This sensing

option offers additional environmental protection for the wheel

speed sensor, but presents special service considerations for

equipment users.

ISO Connector A multi-pin tractor-trailer electrical connector used in Europe

that meets International Standards Organization (ISO) require-

ments. This connector carries power, failure lamp status, and

serial communications to and from European trailer ABSs. The

ISO 7638 connector, for example, provides a dedicated ABS

power source for European tractor-trailers. The ISO 3731

connector is used by a North American manufacturer for ABSs

as well.

J560 Connector See Seven-Pin Connector.

J1587 An SAE Recommended Practice for applications dealing with

the J1708 serial data bus. This standard deals with the assign-

ment of specific parameter codes including diagnostics and

other system attributes. SAE J1587 and J1708 must be used

together to fully implement the noncritical data exchange on

heavy vehicles. See J1708.