Technical information

■

Technician Guidelines for Antilock Braking Systems

■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■

• four sensors/four modulators (4S/4M),

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

• six sensors/six modulators (6S/6M).

Common configurations for trailers are 2S/1M, 2S/2M, 4S/

2M and 4S/3M.

D. ABS Malfunction Indicator Lamps

Vehicles required to have an ABS must have ABS

malfunction indicator lamps. These lamps must be yellow and

light up when the ABS has a “malfunction that affects the

generation or transmission of response or control signals” in

the ABS.

ABS malfunction indicator lamps are not required to light up

for every type of malfunction. However, they are required to

light up for short periods of time for a bulb check whenever the

ABS starts to receive electrical power. The warning lamps for

trailers and dollies are not required to light up for a bulb check

unless the vehicle is stopped.

All trailers/dollies built on or after March 1, 1998 must

feature an external ABS malfunction indicator lamp as part of

the ABS. All new trailers must be capable of activating an in-cab

trailer warning lamp beginning in March 2001. The

requirement for an external trailer/dolly indicator lamp expires

in March 2009.

In-cab ABS indicator lamps are typically located on the

instrument panel. The exact location and appearance vary by

vehicle/component manufacturer. Consult the manufacturer’s

service information for specifics.

E. ABS Diagnostics

Although not required by law, all air brake ABSs have self-

diagnostic capability. On truck-tractors and single-unit or

straight trucks, an ABS provides this information to technicians

through the malfunction indicator lamp and/or an electronic

diagnostic tool, which plugs into an on-board diagnostic

connector. The connector is typically located inside the tractor

cab just underneath the left end of the instrument panel. It is

usually the same connector that’s used to troubleshoot

electronic engines.

Truck-tractors and trucks may also use the ABS malfunction

indicator lamp to signal stored fault information through a blink

code. Vehicles using this system have a switch to activate the

ABS In-cab Malfunction

Indicator Lamp

(ABS)