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Peugeot 405. Manual - part 45
23 Anti-lock braking system
(ABS) - general information
General
1 ABS is available as an option on certain
models covered by this manual, and is fitted
as standard equipment on some models. The
purpose of the system is to prevent the
wheel(s) locking during heavy braking. This is
achieved by automatic release of the brake on
the relevant wheel, followed by re-application
of the brake. The system comprises an
electronic control module, a hydraulic
modulator block, the hydraulic solenoid
valves and accumulators, the electrically-
driven pump, and the roadwheel sensors.
2 The system operates on all four wheels,
and vehicles may be fitted with rear disc or
rear drum brakes.
3 The system prevents wheel lock-up by
regulating the hydraulic pressure to the
brakes.
4 Solenoids (which control the fluid pressure
to the calipers) are controlled by the electronic
control unit, which itself receives signals from
the wheel sensors (fitted to all four wheels),
which monitor the speed of rotation of each
wheel. By comparing these speed signals
from the wheels, the control unit can
determine the speed at which the vehicle is
travelling. It can then use this speed to
determine when a wheel is decelerating at an
abnormal rate, compared to the speed of the
vehicle, and therefore predicts when a wheel
is about to lock. During normal operation, the
system functions in the same way as a non-
ABS braking system.
5 The ABS system is fail-safe, and should a
failure occur, a self-monitoring test facility is
incorporated in the system which can be used
in conjunction with dealer test equipment for
fault diagnosis.
6 Three different types of ABS may be fitted,
depending on model, as follows.
Bendix “integral” ABS
7 This system is fitted to certain models up to
1993 as standard equipment. The system is
fitted instead of a conventional system, and
the brake pedal acts directly on the hydraulic
control unit, which replaces the master
cylinder and vacuum servo in a conventional
braking system.
8 The system operates at very high fluid
pressure, typically 158 to 183 bar, generated
by an electric pump fitted to the modulator
assembly.
9 The system is fail-safe and will continue to
operate even if one wheel sensor should fail.
In the event of total failure, the control unit will
revert the system to normal braking.
Bendix “additional” ABS
10 The Bendix “additional” system is fitted as
an option to certain models, and the ABS
components are fitted in addition to the
conventional braking system components.
11 The system uses the pressure provided
by the conventional master cylinder and
vacuum servo.
12 The system is fail-safe, and conventional
braking is maintained through the servo
and master cylinder in the event of an ABS
failure.
13 The braking system can be safely bled,
and the fluid can be renewed as described in
Chapter 1, as the system operates using the
conventional pressure supplied by the master
cylinder and servo.
Bosch 2E “additional” ABS
14 The Bosch 2E additional system is fitted
to certain later models from 1993, and is
similar to the Bendix “additional” system
described previously.
24 Anti-lock braking system
(ABS) components - removal
and refitting
4
Front wheel sensor
Removal
1 Disconnect the battery negative lead.
2 To improve access, apply the handbrake,
then jack up the front of the vehicle and
support securely on axle stands (see “Jacking
and Vehicle Support”). If desired, remove the
roadwheel.
3 Trace the wiring back from the sensor, then
disconnect the sensor wiring connector (on
most models, the sensor wiring is routed
through the inner wing panel, and the
connector is located in the engine
compartment.
4 Release the sensor wiring from any
securing clips and, where applicable, push
the wiring grommet from the inner wing panel
and feed the wiring through the panel.
5 Unscrew the securing bolt, and withdraw
the sensor from the hub carrier (see
illustration).
Refitting
6 Before refitting a sensor, ensure that the tip
is clean. Where applicable, on new sensors
remove the protective sticker from the tip.
7 Fit the sensor to the hub carrier.
8 Clean the sensor securing bolt, then apply
thread-locking compound to the bolt threads.
Fit the bolt and tighten to the specified torque.
9 On models fitted with the Bendix “integral”
ABS system, proceed as follows (see
illustration).
a) Loosen the sensor adjuster bolt.
b) Position a 0.5 mm feeler blade between
the sensor tip and the sensor ring on the
driveshaft.
c) Press the sensor lightly against the feeler
blade, and tighten the adjuster bolt to the
specified torque.
d) Remove the feeler blade.
10 On completion, where applicable refit the
roadwheel and lower the vehicle to the
ground.
Rear wheel sensor
Removal
11 Disconnect the battery negative lead.
12 To improve access, chock the front
wheels, then jack up the rear of the vehicle
and support securely on axle stands (see
“Jacking and Vehicle Support”).
13 Trace the wiring back from the sensor,
then disconnect the sensor wiring connector
(on most models, the sensor wiring is routed
through the floor of the vehicle, and the
connector is located behind the luggage
compartment side trim panel.
14 Release the wiring from the clips
underneath the vehicle, and feed the wiring
through the floor panel.
Braking system 9•19
24.9 ABS front wheel sensor adjustment
(adjuster arrowed) - Bendix “integral” ABS
24.5 ABS front wheel sensor
(arrowed)
9
Warning: Due to the complexity
of the system, the very high
fluid pressures involved, and the
need for special bleeding
equipment and pressure gauges, any
operation requiring removal or
disconnection of any hydraulic
component, pipe or fitting must only be
carried out by a suitably-equipped
Peugeot dealer. Failure to heed this
warning may result in personal injury, or
malfunction of the system at a critical
time. Work on vehicles equipped with the
Bendix “integral” ABS should therefore be
confined to routine maintenance
operations.