Technical information

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Technician Guidelines for Antilock Braking Systems
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blink code system. Other ABSs may also have light-emitting
diode (LED) lamps on the ECU to indicate problems.
ABSs used on trailers sometimes have a place to connect an
electronic diagnostic tool. The connector is either on a pigtail to
the ECU, on the outside of the ECU, or inside the ECU box.
Others have either LED lamps on the ECU box or number
codes displayed inside the ECU which give diagnostic
information.
F. Traction Control Systems
Traction control systems are designed to prevent wheel spin
in the power mode. Traction control attempts to regain traction
by braking the spinning wheels, and sometimes throttling back
engine power. Unlike an ABS, traction control can automatically
apply the brakes. The driver does not need to depress the brake
pedal for traction control to engage.
Traction control electronics are integrated into the ABS ECU.
The system applies the brakes on the spinning wheel(s) when
the wheel speed sensors tell the ECU that a wheel is
accelerating at a much faster speed than the wheel on the other
end of the axle. It does this by energizing a solenoid valve,
which directs reservoir pressure to the relay valve and
simultaneously activates the modulator valves to keep air
pressure from the brake chambers. The ECU then directs the
modulator valve to open, and pulse air into the brake chamber
on the spinning wheel until wheel speed balance is regained.
On some systems, the ECU will throttle back engine power
if both wheels are spinning too fast. If all the drive wheels on a
tractor are spinning too fast, the tractor can become unstable,
spin or jackknife. Traction control is especially valuable when a
light drive wheel load might allow the wheels to spin under
power, or when a tractor is pulling multiple trailers.
Traction control systems
are designed to prevent
wheel spin in the power
mode.
Unlike an ABS, traction
control
can apply the
brakes automatically.
The driver does not
need to depress the
brake pedal for traction
control to engage.
Traction control is not
required by law, but it is
a common ABS option.