Anti-Lock Braking And Traction Control System Components; Hydraulic Modulator; Electronic Control Unit (Ecu); Wheel Speed Sensors - Opel Zafira B MPV 2006 Owners Workshop Manual

9•16 Braking system
18.5 Disconnect the wiring harness plug
(arrowed) from the ECU
braking. This is achieved by automatic release
of the brake on the relevant wheel, followed
by re-application of the brake.
The solenoid valves are controlled by the
ECU, which itself receives signals from the
four wheel speed sensors which monitor
the speed of rotation of each wheel. By
comparing these signals, the ECU 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
conventional braking system.
If the ECU senses that a wheel is about to
lock, it operates the relevant solenoid valve(s)
in the hydraulic unit, which then isolates from
the master cylinder the relevant brake(s) on the
wheel(s) which is/are about to lock, effectively
sealing-in the hydraulic pressure.
If the speed of rotation of the wheel
continues to decrease at an abnormal rate,
the ECU operates the electrically-driven pump
which pumps the hydraulic fluid back into the
master cylinder, releasing the brake. Once
the speed of rotation of the wheel returns to
an acceptable rate, the pump stops, and the
solenoid valves switch again, allowing the
hydraulic master cylinder pressure to return to
the caliper, which then re-applies the brake.
This cycle can be carried out many times a
second.
The action of the solenoid valves and return
pump creates pulses in the hydraulic circuit.
When the ABS system is functioning, these
pulses can be felt through the brake pedal.
On models with traction control, the ABS
hydraulic modulator incorporates an additional
set of solenoid valves which operate the
traction control system. The system operates
at speeds up to approximately 30 mph using
the signals supplied by the wheel speed
sensors. If the ECU senses that a driving
wheel is about to lose traction, it prevents this
by momentarily applying the relevant front
brake. The ABS ECU also communicates with
the engine management ECU during traction
control operation. In severe cases of traction
loss the engine management ECU will reduce
engine power to assist with traction recovery.
The electronic stability program (ESP) is
a further development of ABS and traction
control. Using additional sensors to monitor
steering wheel position, vehicle yaw rate,
acceleration and deceleration, in conjunction
with the ABS sensors, the ECU can intervene
under conditions of vehicle instability. Using
the signals from the various sensors, the ECU
can determine driver intent (steering wheel
position, throttle position, vehicle speed and
engine speed). From the sensor inputs from
the wheel speed sensors, yaw rate sensors
and acceleration sensors the ECU can
calculate whether the vehicle is responding
to driver input, or whether an unstable driving
situation is occurring. If instability is detected,
the ECU will intervene by applying or releasing
the relevant front or rear brake, in conjunction
with a power reduction, until vehicle stability
returns.
The operation of the ABS, traction control,
and stability programs is entirely dependent
on electrical signals. To prevent the system
responding to any inaccurate signals, a
built-in safety circuit monitors all signals
received by the ECU. If an inaccurate signal
or low battery voltage is detected, the system
is automatically shut down, and the relevant
warning light on the instrument panel is
illuminated, to inform the driver that the
system is not operational. Normal braking is
still available, however.
If a fault develops in the ABS/traction
control/ESP system, the vehicle must be taken
to a Vauxhall/Opel dealer for fault diagnosis
and repair.
Note 1: Faults on the ABS system can only
be diagnosed using Vauxhall!Opel diagnostic
equipment or compatible alternative
equipment.
Note 2: Before starting work, refer to the note
at the beginning of Section 2 concerning the
dangers of hydraulic fluid.
Hydraulic modulator
1
Remove the windscreen cowl panel as
described in Chapter 11.
2 Remove the battery and battery tray as
described in Chapter 5A.
3 Release the locking clip, then lift up the
cooling system expansion tank and remove it
from the mounting bracket. Place the tank to
one side.
4 Minimise fluid loss by first removing the
master cylinder reservoir cap and screwing it
down onto a piece of polythene.
5 Pull out the locking bar and disconnect
the wiring harness plug from the ECU (see
illustration).
6 Note and record the fitted position of the
brake pipes at the modulator, then unscrew
the union nuts and release the pipes. As a
precaution, place absorbent rags beneath the
brake pipe unions when unscrewing them.
Suitably plug or cap the disconnected unions
to prevent dirt entry and fluid loss.
7
Unscrew the three retaining bolts and
remove the hydraulic modulator from the
mounting bracket.
8 Refitting is the reverse of the removal
procedure, noting the following points:
a) Tighten the modulator retaining bolts to
the specified torque.
b) Refit the brake pipes to their respective
locations, and tighten the union nuts to
the specified torque.
c) Ensure that the wiring is correctly routed,
and that the ECU wiring harness plug is
firmly pressed into position and secured
with the locking bar.
d) Refit the battery tray and battery as
described in Chapter SA.
e) Refit the windscreen cowl panel as
described in Chapter 11.
f) On completion, bleed the complete hyd-
raulic system as described in Section 2.
Ensure that the system is bled in the
correct order, to prevent air entering the
modulator return pump.
Electronic control unit (ECU)
Note: At the time of writing, no information
was available for removal and refitting of the
ECU on systems incorporating an electronic
stability program (ESP). This work should
therefore be entrusted to
a
Vauxhall!Opel
dealer.
9 Remove the hydraulic modulator from the
car as described previously in this Section.
10 Undo the three retaining bolts and
carefully withdraw the ECU from the base
of the hydraulic modulator. Note that new
retaining bolts will be required for refitting.
11
Carefully remove the eight sealing rings
from the modulator valves and obtain new
sealing rings for refitting.
12
Locate the new sealing rings over the
solenoid valves, then carefully place the ECU
in position, keeping it square and level.
13 Fit the three new retaining bolts and
tighten securely.
14 On completion, refit the hydraulic
modulator as described previously in this
Section.
Wheel speed sensors
15 The front and rear wheel speed sensors
are an integral part of the hub bearings and
cannot be separated.
16
Refer to Chapter 10 for front and rear hub
bearing removal and refitting procedures"
Yaw rate/acceleration sensor
Note: The yaw rate/acceleration sensor is only
fitted to vehicles equipped with an electronic
stability program (ESP).
17 Disconnect the battery negative terminal
(refer to Disconnecting the battery in the
Reference Chapter).
18 Remove the centre console as described
in Chapter 11.