parking lock cannot be engaged, there is a risk of the vehicle
rolling away, and the parking brake should be applied.

643_029

Deactivating the emergency release (P-ON position)
The emergency release mechanism is deactivated in reverse
order.

643_030

44

Operation
1. Remove inlay from cupholder.

Inlay in cupholder

2. Remove the cover with a screwdriver. Remove the screw, push the
release tab (arrow) and take out the cover.

3. Fold the socket wrench as shown and insert it into the actuating
mechanism.

Cover

Socket wrench

643_031

4. Fold the special socket tool as shown and move it into position.

Direction of travel

643_032

643_033
45

Oil system and ATF supply
The 0BZ transmission has a common ATF oil system for all
functional sub-assemblies and oil chambers of the gearbox.
The Mechatronic module has its own oil chamber in which its
own oil level is established. See page 48.
The following functional sub-assemblies are supplied and/or
controlled, lubricated and cooled with ATF.
››
››
››
››
››
››

The special ATF and the ATF pressure filter currently have a
service/replacement interval of approximately 40,000 miles
(60,000 km) (the ATF intake filter is not replaced). In order to
be able to drain off the used oil as completely as possible, the
0BZ gearbox has several ATF drain plugs.
Note: when changing the ATF, all drain plugs always have to
be removed.

Mechatronic module.
Dual clutch.
Hydraulic selector mechanism.
Hydraulically operated parking lock.
Gear set (gear train).
Final drive with differential lock.

ATF filter
›› with heat shield
(partial-flow pressure filter)
Make sure the heat shield is
always installed. Otherwise,
there is a risk of damage to the
transmission.

ATF drain plug
for Mechatronic module oil chamber

There may also be a drain
plug here, depending on
version.

ATF intake filter –
integrated in ATF sump

ATF drain plugs
643_056

Note on draining the ATF
There are different versions of the ATF drain plugs and the
overflow pipe. Follow the instructions given in the workshop
manual, ETKA and on the VAS Scan Tool when checking and
changing the ATF.

Overflow pipe

ATF inspection and drain plug

643_057

46

ATF pump
One of the most important components of an automatic
transmission is the ATF pump.
The 0BZ transmission is supplied with oil by an ATF pump
that is constantly driven by the engine (internal gear pump).
The ATF pump is driven by a spur gear system of which the
drive gear is attached to the clutch housing. See page 22,
Figure 643_039.

The ATF pump is part of the auxiliary hydraulic module. See
page 54.

Oil pipe connections
to parking lock module

Oil pipe to clutch cooling circuit for clutch K2

Oil pipe connections to
and from
Mechatronic module

Bracket/
securing clip

643_058

ATF filtration

Intake connection –
connected directly to ATF
intake filter

The ATF is filtered by an intake filter integrated in the ATF
sump and a partial-flow pressure filter through which the
return flow from the ATF cooler passes. Part of the cooled
and filtered ATF is diverted by the Mechatronic module used
directly to control the clutch cooling circuit for clutch K2.

Pipe to clutch cooling circuit
Clutch K2

ATF filter
Partial-flow pressure filter
643_059

47

Oil level
On the 0BZ gearbox, the Mechatronic module is in its own oil
chamber, which is formed by a partition dividing it off from
the gear train. In operation, that oil chamber (Mechatronic
module oil chamber) fills with ATF until it is largely or completely (depending on gearbox version) immersed in ATF. That
ensures that the hydraulic system is well vented and the
Mechatronic module always operates under the same physical
conditions. In addition, the solenoid valve coils are effectively
cooled.
The Mechatronic module oil chamber fills up with exhaust oil
from normal operation of the solenoid valves and is thus
continually filled. An overflow facility provides for venting
and a defined oil level in the Mechatronic module oil
chamber.
Version A
- transmission codes NXZ and PTX

There are two transmission versions with differing accumulation levels:
›› Version A – Transmission codes NXZ and PTX
The apertures in the partition for the two lower gear-shift
actuator travel sensors and for the two speed sensors are
sealed by means of sealing collars. The apertures for the two
upper gear-shift actuator travel sensors are not sealed (no
sealing collars installed) and the left aperture is enlarged.
The ATF accumulates until it reaches the upper apertures, at
which point is runs off into the gear train oil chamber.

Enlarged aperture for
oil overflow

View of partition
On version A, the apertures in the partition for the upper travel sensors act as
the oil overflow.

There are no sealing collars installed on
the two upper travel sensors.

Oil level in Mechatronic
module oil chamber

Oil level in gear train oil chamber1)

643_093

48

Version B
- all transmission codes EXCEPT NXZ and PTX

Overflow channel

View of partition
On version B the apertures in the partition for the upper travel
sensors are an exact fit and are sealed.

Gear-shift actuator A – gears 5/1

Overflow channel

The sealing collars on the two
upper travel sensors have to be
installed on as shown (tab at the
top).

Mechatronic module oil
chamber completely filled

643_094

Oil level in gear train oil chamber1)

With this version, all apertures in the partition are sealed by
sealing collars. At the very top of the Mechatronic module oil
chamber there is an overflow channel through which the
exhaust oil flows off into the gear train oil chamber. With
version B, therefore, the Mechatronic module oil chamber
fills up completely with accumulated oil (ATF) and the oil
1)

level is raised to a point where it is above the highest gearshift actuator (gear-shift actuator A for gears 5/1).
The effect is that gear-shift actuator A is better filled and
vented. That, in turn, improves the quality of gear changes in
gears 1 and 5.

he oil level in the gear train oil chamber varies according to the operating conditions. The oil level shown here reflects the required level under the specified
T
inspection conditions.

Information for all transmission codes

›› The oil chamber has its own drain plug. Observe the guidance notes on page 46.
›› A new Mechatronic module is always supplied with only 4 sealing collars. The two upper sealing collars (on the upper
travel sensors) are obtainable from the ETKA and have to be installed if necessary.
Information for transmission codes NXZ and PTX only

›› With these versions, the Mechatronic module is installed without sealing collars on the upper travel sensors.
Information for all transmission codes except NXZ and PTX

›› With these versions, the sealing collars have to be installed as shown on the upper travel sensors before the
Mechatronic module is installed so the ATF can accumulate as required in the Mechatronic module oil chamber.
49

Lubrication and cooling of the gear train
Lubrication of the gear train is performed by a selectively
targeted injection system that lubricates only the gear train
subset that is transmitting the drive at any one time, each
gear train subset is allocated a separate oil pipe. Depending
on which clutch is in operation (K1 or K2), a change-over
valve in the Mechatronic module controls the oil flow to the
relevant gear train subset. In the oil pipe there are small
injector jets which deliver ATF to the drive gears for lubrication and cooling.

The gear pairings that are permanently engaged and the two
input shafts with their idler gear bearings and synchromesh
mechanisms are supplied separately and continuously with
cooled oil. See hydraulic circuit diagram on page 74.

Gearbox unit 1
Gearbox unit 2

Oil pipe –
gear train subset 1

Oil pipe –
gear train subset 2

50

Lubrication and cooling of the final drive
Pinion top bearing

Oil pan

Overflow pipe

Intake point – sump

643_060

The relatively high oil chamber for the final drive is filled by
the cooling oil from the dual clutch. The dual clutch throws
large quantities of its cooling oil into the final drive oil
chamber via an oil baffle plate (not illustrated).
The rotating ring gear moves surplus oil into an oil collector
from where it can run back to the intake point through the
hollow pinion shaft. In addition, the oil level is limited by an
overflow pipe.
The pinion top bearing is supplied via another oil collector.

643_061

51

ATF temperature management
The ATF cooling system uses two heat exchangers – one
coolant/oil heat exchanger (ATF cooler 1) and one air/coolant
heat exchanger (ATF cooler 2).
ATF cooler 1 is connected in series in the partial-flow ATF
circuit for the ATF pressure filter and the ATF flows through it
constantly. The cooling capacity of ATF cooler 1 is substantially
increased by ATF cooler 2. The two heat exchangers are connected in series and integrated in the engine cooling system.
The coolant flow through the two heat exchangers is controlled by means of a coolant thermostat (bypass thermostat).
After-Run Coolant Pump V51 assists the flow of coolant
through the two ATF coolers.

ATF cooler 2
›› Air/coolant heat exchanger

After-Run Coolant Pump V51
V51 operates as required for the following conditions:
›› For continued coolant circulation.
›› To increase heating capacity.
›› To increase the cooling capacity of the ATF cooling system.
It is operated on demand by the ECM via a PWM signal. Above
an ATF temperature of approximately 204 °F (96 °C), the ECM
instructs V51 to operate. V51 increases the coolant flow rate
through the two ATF coolers and the cooling capacity is then
increased in proportion with the pump delivery rate. If the
ATF temperature drops to around approximately 197 °F
(92 °C), the pump delivery requirement is cancelled. If there
is no other demand for pump operation within the thermal
management system, V51 is switched off.

After-Run Coolant Pump
V51

52

The coolant thermostat opens at approximately 176 °F
(80 °C). When the coolant thermostat is open, the coolant
cooled by the motion-induced air flow over ATF cooler 2 flows
to ATF cooler 1. ATF cooler 2 substantially reduces the
coolant temperature before it is fed into ATF cooler 1. Due to
the low inflow temperature, ATF cooler 1 is able to operate
very efficiently.

Coolant thermostat closed up to approximately 176 °F
(80 °C)

Heat shield1)

The flow through the two heat exchangers is kept to a
minimum. Engine and transmission quickly reach operating
temperature.

Coolant thermostat
›› Bypass thermostat
›› Pay attention to installation
orientation

643_096

Coolant thermostat open at approximately 176 °F (80 °C)
(as illustrated)
Coolant flows through both heat exchangers. The ATF is
effectively cooled.
1)

he heat shield acts, as a protective guard for the component and, secondly
T
prevents the coolant and the coolant thermostat being heated too much by
the exhaust system. That prevents unintended opening of the thermostat.
Therefore, you should pay careful attention to correct installation of the heat
shield.

ATF cooler 1
›› Coolant/oil heat exchanger

643_095

53

Transmission control
Component overview
The Mechatronic module is the central transmission control
component. It originates from the DQ500 transmission series
(for example, the 7-speed dual clutch transmission OBH). To
meet the functional requirements of the OBZ transmission,
additional components have been added. One particular
feature is that that transmission control system utilizes two
control modules.
The electro-hydraulic transmission control system uses the
following components/modules:
››
››
››
››
››

Dual-Clutch Transmission Mechatronic J743.
Auxiliary hydraulic module.
Parking lock module.
Transmission Control Module 2 J1006.
Selector mechanism.

Those components/modules have the following functions:

Dual-Clutch Transmission Mechatronic J743

Parking lock module

J743 is the central control module and master for Transmission Control Module 2 J1006. See pages 57 and 65.
It is responsible for hydraulic pressure control for the following subsystems:
››
››
››
››

Clutch control system for clutches K1 and K2.
Clutch cooling system for clutch K1. See also page 26.
Gear shifting.
Demand-based gear set lubrication.

Auxiliary hydraulic module
The auxiliary hydraulic module performs the following tasks:
›› Oil supply (ATF pump) for gearbox control, lubrication and
cooling.
›› Control of cooling oil for clutch K2.
›› Partial control of the pressure for the parking lock.

Parking lock module

Transmission Control Module 2 J1006
J1006 performs the following tasks:
›› Electrical operation of the parking lock module.
›› Electrical operation of the clutch cooling system for clutch
K2 (via Gearbox Control Unit 1 J743 and the auxiliary
hydraulic module; see page 26).

The parking lock module performs the following tasks:
›› Partial control of the pressure for the parking lock.
›› Electro-hydro-mechanical actuation of the parking lock.

Transmission Control Module 2 J1006

54

Selector mechanism
The selector mechanism performs the following tasks:
›› Registering driver input for control of the transmission.
›› Shift-lock functions and indication of transmission settings.

Selector mechanism

Dual-Clutch Transmission Mechatronic and
Gearbox Control Unit 1 (both referenced as J743)

Auxiliary hydraulic module

643_065
55

Dual-Clutch Transmission Mechatronic
J743 consists of two modules:
›› The electronic module containing Gearbox Control Unit 1
and the majority of the sensors.
›› The electro-hydraulic control module containing the majority of the actuators.
The Mechatronic module is compatibly matched combination
of those two modules and may, therefore, only be replaced as
a complete unit.

Electrical connector for Transmission Input Speed
Sensor G182 and Clutch Temperature Sensor 2
G659

Electrical connector T16c
for vehicle and transmission peripherals

Printed circuit board
for the solenoid valves (actuators)

Electronic module – see page
64

Electro-hydraulic control module

643_066

When handling the Mechatronic module, it is important to pay close attention to the working guidelines regarding electrostatic discharge (ESD). Electrostatic discharge can irreparably damage electronic components.

56

The Mechatronic module controls, regulates and/or executes
the following functions:
›› Adjustment of the oil pressure in the hydraulic system to
suit the various needs and requirements.
›› Control of the dual clutch.
›› Control of the clutch cooling system for clutch K1.
›› Control of the clutch cooling system for clutch K2.1)
›› Shift point selection.
›› Gear shifting.
›› Serving as master J1006.
›› Control of the parking lock.1)
›› Communication with the other control units in the vehicle.
›› Safe mode program.
›› Self-diagnostics.
1)

peration/activation is performed by Transmission Control Module 2 J1006.
O
See page 26 and the schematic diagram on page 72
Electro-hydraulic control module

Electronic module – see page 64

Electrical connection between Gearbox
Control Unit 1 and the solenoid valves
(actuators) takes place via the printed
circuit board.

Electrical connector for
printed circuit board

Gearbox Control Unit 1
(also referenced as J743)
643_067

The gasket for the interfaces between the hydraulic control module and the gearbox housing is printed on the intermediate
plate and cannot be replaced. When the Mechatronic module is detached, the gasket is damaged, which means that a proper
seal can no longer be obtained. Re-using such a Mechatronic module is not permissible. See page 59.

57

Electro-hydraulic control module
The electro-hydraulic control module contains the majority of
the solenoid and pressure regulating valves, hydraulic valves
and other valves for controlling the transmission functions.
See hydraulic circuit diagram on page 74.

The electro-hydraulic control module controls, regulates and/
or executes the following functions:

The description of the valves can be found on page 60 and
the section for the relevant function.

›› Pressure control for operating clutches K1 and K2.