The ABS 5.4 system in brief
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The ABS 5.4 system in brief
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ABS brakes (Antilock Braking System) have been
developed to provide optimum braking with no loss of directional
stability under widely varying conditions. The stopping distance of
a car is influenced by a variety of factors, including weather
conditions, road surface, prevailing traffic conditions and the
amount of brake pressure applied.
The ABS is a control system that gives modern brake
systems the ability to harness the maximum braking effect of the
vehicle in critical situations, regardless of the road conditions.
The main advantages of the ABS system are:
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No loss of directional stability on braking.
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Steering control retained even during heavy braking.
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Shortest possible braking distance.
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The Saab 9-5 is equipped with the ABS 5.4 system, which
is a dual-circuit, four-port brake system containing the following
principal components:
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Wheel sensors (one on each wheel).
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ABS hydraulic unit with the following integral components:
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Valve block with one inlet and one outlet valve for each
wheel
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Return pump comprising electric motor and pump unit.
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Control module with integral master and pump relay.
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A wheel sensor on each wheel generates an alternating
current, the frequency of which increases with increasing wheel
speed. The ABS control module, which receives signals for wheel
speed, continuously computes wheel acceleration, retardation, road
speed and wheel slip (degree of lock-up). When a wheel comes
close to the lock-up threshold, the control module activates the
inlet/outlet valves and the return pump, thus modulating the brake
pressure for the wheel in question, and enabling the maximum
braking effect to be achieved without loss of steering control.
The control module incorporates a function known as
electronic brake-force distribution (EBD), which controls the rear
inlet valves such that the maximum braking effect is achieved on
the rear wheels under different load conditions, without the risk of
their locking up before the front wheels.
Several other systems in the car also need data on the
vehicle's road speed. The MIU receives a signal, via a lead
connected to the rear left wheel-speed sensor, which it then
converts to km/h, a computation that includes a preprogrammed
correction for tyre size. Because the MIU is connected to a bus, all
the other control modules connected to the bus are able to share the
RL wheel-speed and milometer (odometer) data.
The control module continuously monitors both its own
internal functions and the functioning of the other system
components. If a fault is detected, a diagnostic trouble code (DTC)
will be generated, the ABS warning lamp will come on and the
ABS system will be disabled.
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Note
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The function of the ABS warning light is to be changed during the 1998 model year. After the new function has been introduced, when the ABS warning light comes on, this will also cause both the standard brake warning light and the central warning light to come on. The circuitry between the ABS control module and the MIU will remain unchanged.
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