ISIS steering column control center (SZL) and multifunction steering wheel (MFL)

The functions of the SZL (steering column control center) can be subdivided into three main blocks:

SZL as an ISIS satellite with connection to the BYTEFLIGHT bus (ISIS is the Intelligent Safety Integration System)
The SZL as the switchboard for the control functions on the steering column:
- semi/fully electrical steering wheel adjustment -> via the button on the left-hand side of the steering column
- steering wheel heater -> via the button on the left of the steering column
SZL as steering-angle sensor.

The multifunction steering wheel (MFL) provides the means by which the driver can easily and ergonomically perform the following functions:

audio, telephone, Steptronic, fanfare horn and a definable button -> via the function buttons of the multifunction steering wheel
direction indicators / high beam headlights, gear selector lever, windshield wiper, cruise control (FGR), -> via the 4 control levers on the steering column

Brief description of components

The multifunction steering wheel (MFL) consists of

4 steering-column levers: All steering-column levers are incremental keys and no longer lock in the operated position
Fanfare
4 Steptronic buttons
2 blocks with function keys
Airbag system
Heating coil and temperature sensor in the steering wheel rim

Located below the multifunction steering wheel are

2 buttons on the left of the steering column (steering wheel adjustment, steering wheel heater)
SZL (steering column control center) control module with integral steering angle sensor

The electronic control system for the steering column control center and the multifunction steering wheel is divided between two electronic modules:

Steering column module (= SZL)
Steering wheel module

Signal transmission from the steering wheel module to the steering column module is effected by means of a coil-spring conductor.

Steering column stalk, top left: Turn indicator-low beam switch

The turn signal/dip switch consists of a steering column stalk with two integral axial touch switches.

Function	Operation
one-touch indicating	Touching lever up/down
continuous flashing	press up/down beyond point of resistance
Parking light	press up/down beyond point of resistance
High beam	touch forwards (only when headlights are on)
Headlamp flasher	touch lever backwards

The turn signal/dip switch also incorporates two axial touch switches .

The top button activates the Info display on the right of instrument cluster below the tachometer. This Info display shows information such as average fuel consumption and average speed. The top button hides the Info display or retrieves stored Check Control messages:
High-priority Check Control messages are automatically shown on the Info display. Low-priority Check Control messages are retrieved/scrolled by means of the top button.
The bottom button activates the Info display on the left of instrument cluster below the speedometer. This Info display shows information such as remaining fuel and range.

Transfer concept: steering column stalks and axial touch buttons have differing signal transmission routes:

Steering column stalk signal transmission route: When the driver operates the steering column stalk, a message is sent to the light module. Signal path: From SZL (steering column control center) -> BYTEFLIGHT data bus -> SIM (safety information module) -> BYTEFLIGHT data bus -> ZGM (central gateway module) -> System K-CAN data bus -> LM (light module).

For safety reasons, there is an additional serial cable from the SZL to the LM. An analogue coded signal is applied to that cable and is analyzed by the light module. Each switch position is allocated a voltage range. The serial cable enables transmission of all positions of the turn signal/dip switch in the event of a bus fault, though with some limitations to the possible functions:

High beam and headlamp flasher only function if the steering column stalk is held in position.
The direction indicators only function while the steering column stalk is held in position, no continuous flashing, no automatic reset
No hazard-warning lights in the event of a crash and when arming the antitheft alarm.

Touch button signal transmission path: When the driver operates one of the axial touch buttons, a message is sent to the instrument cluster.

Signal path: From SZL (steering column control center) -> BYTEFLIGHT data bus -> SIM (safety information module) -> BYTEFLIGHT data bus -> ZGM (central gateway module) -> System K-CAN data bus -> Instrument cluster.

Steering-column lever, bottom left: vehicle speed control

The steering-column lever for cruise control increases or reduces the traveling speed.

Cruise control is available with the ”ACC (Adaptive Cruise Control)” option.

Function	Operation without ACC	Operation with ACC
Switch from cruise control OFF to cruise control ON and set the current speed. If the cruise control is already switched on, the set speed is increased/reduced.	One-touch forwards/backwards	One-touch forwards/backwards
Switch from cruise control OFF to cruise control ON and set the current speed. If the cruise control is already switched on, the next highest / lowest stored speed stage is set.	Overpress forwards/backwards
Calls up stored speed	Touch lever inwards	Touch lever inwards
Sets or deletes speed stage	Press inwards and hold (for at least 3 seconds)
Switches off cruise control	Touching lever up/down	Touching lever up/down
Change distance setting		Turn adjuster wheel

Speed marks of required speeds: the steering-column lever for cruise control can also be used to select required speeds. Required speeds are e.g. frequent speeds used, such as 30 km/h, 50 km/h, 60 km/h. Speed marks can be set and stored for these required speeds.

The preset cruise control speeds are car & key memory functions, i.e. they can be set and stored individually for each driver.

Programming required speed: It is best to program required speeds when the vehicle is stationary! Reason: when the vehicle is moving, the speed entered as required speed is set immediately!

Activating the programming function: overpress the steering-column lever for cruise control (in direction of travel or against direction of travel).
Selecting required speed: an arrow appears in the speedometer of the instrument cluster. To increase the required speed, the cruise control steering-column lever must be pressed forwards up to the pressure point. To decrease the required speed, press the lever backwards up to the pressure point.
Storing required speed: press and hold the axial button for at least three seconds. The stored required speed is indicated by a speed marker on the speedometer (gray arrow).

Deleting required speed:

Activating the programming function: overpress the steering-column lever for cruise control (in direction of travel or against direction of travel). An arrow then appears on the speedometer.
Select the speed marker to be deleted with the arrow. The arrow on the speed marker turns white.
Press and hold the axial button for at least three seconds. The speed marker is deleted.

Transfer concept: When the driver operates the steering column stalk, the axial button or the adjuster wheel (if ”Adaptive Cruise Control” option fitted), a message is sent to the DME (digital engine electronics module) or the ACC control module.

Signal path: From SZL (steering column switch center) -> data bus BYTEFLIGHT -> SIM (Safety Information Module) -> data bus BYTEFLIGHT -> ZGM (Central Gateway Module) -> data bus PT-CAN -> DME or ACC.

Steering-column lever, top right: selector lever

The gear selector lever is used for fully electronic selection of the gear positions R - N - D and P (reverse gear - neutral position - drive - park position).

The desired drive position is registered by seven Hall sensors. The Hall sensor are configured in such a way that if an individual Hall sensor fails the operability of the gear selector lever is retained.

The gear selector lever involves the following functions

Function	Operation
Drive position D (Drive)	Overpress downwards
Drive position R (reverse gear)	Overpress upwards
Drive position N (neutral position):	from drive position P: one-touch upwards or downwards from drive position D: one-touch upwards from drive position R: one-touch downwards
Position P (park position)	Touch lever inwards

Information displayed to the driver

Gear shift pattern in the gear selector lever: the gate pattern is illuminated by locator lighting
The current gear position in the center field of the instrument cluster
Check Control messages in the information display of the instrument cluster.

Transfer concept: When the driver operates the steering-column lever or the axial one-touch button, a message is sent to the EGS (Electronic Transmission Control) control module.

For reasons of safety, there is also a serial line between the SZL and EGS. The same messages are transmitted across this line as across the buses.

Electronic parking lock: with electronic transmission control, the steering column lock can be eliminated as an antitheft measure: the electronic parking lock replaces the steering column lock.

Electronic parking lock ”emergency” release: in an emergency, the electronic parking lock be unlocked mechanically:

Remove the cover in the driver's side footwell near the left A pillar.
Unlock the electronic parking lock manually.

Steering column stalk, bottom right: Wiper switch

The wiper switch consists of:

Steering-column stalk with
integral axial button
adjuster wheel

The steering column stalk for the windshield wipers incorporates the following functions:

Function	Operation without Rain/Light Sensor	Operation with Rain/Light Sensor
Intermittent wipe	Touch upwards once
Wiper speed 1	Touch upwards twice	Touch upwards once
Wiper speed 2	Touch upwards three times or press upwards beyond point of resistance	Touch upwards twice or press upwards beyond point of resistance
Flick wipe	Touch lever down	Touch lever down
Front wash	touch lever backwards	touch lever backwards
Wipers off	Touch lever inwards
Automatic wipe ON/OFF		Touch lever inwards
Set sensitivity of the rain sensor/light sensor to a choice of 4 levels.		Adjuster wheel with 4 positions
Set intermittent-wipe interval to choice of 4 settings (within each of those 4 settings the actual interval varies according to the vehicle's road speed)	Adjuster wheel with 4 positions

The rain/light sensor is fitted with the ”Rain sensor and automatic headlamp control” option.

When the ignition is switched OFF, the wiper and the rain/light sensor are switched off as well.

Transmission concept: when the driver operates the steering column stalk for the windshield wipers, a message is sent to the wiper module.

When the driver operates the axial button or the adjuster wheel,

on a vehicle without rain/light sensor, a message is sent to the wiper module.
on a vehicle with rain/light sensor, a message is sent to the rain/light sensor control module.

Steptronic buttons

Operating the Steptronic button causes the EGS (Electronic Transmission Control) to shift gear upwards or downwards.

The Steptronic buttons are redundant for safety reasons, one each to the left and right on the multifunction steering wheel.

The Steptronic buttons are only enabled when the S/M key (S = Sport program, M = Manual shift program) on the right of the multifunction steering wheel has been switched to Manual: an M is displayed in the program display of the instrument cluster (display field between speedometer and tachometer). Depending on the gear selection, M1 to M6 appears for the current gear.

The Steptronic buttons (+) in the upper area of the multifunction steering wheel are used for upshifts.
The Steptronic buttons (-) in the lower area of the multifunction steering wheel are used for downshifts.

The Steptronic buttons are Hall sensors.

For reasons of safety, there is also a redundant serial line between the SZL and EGS.

Left-hand function buttons

The function buttons on the left are used for voice input and sound output.

The PTT ("push to talk") button activates the voice input function.
The +/- rocker with the speaker symbol adjusts the volume of the audio system, telephone, TV and navigation system.
The telephone button is used to make or end a telephone call or accept an incoming call.

Function key block, MFL right

The function keys to the right are keys for the choice of various functions:

The S/M key (S = Sport program, M = Manual shift program) changes between: Sport program (S) and Manual shift program (M). If Manual (M) is selected, the driver can use the Steptronic keys to shift up and/or down. The Sport program (S) implements a performance-oriented driving style.
The rocker with the up and down arrows activates
the station search function if the radio is in use,
the next/previous track function if the cassette/CD/minidisk player is in use,
the station list scroll function if the TV is in use,
the phone book scroll function if the telephone is in use.
The bottom button is a programmable-function button with car & key memory function. It can be programd individually for different drivers.
The ”Configuration” menu on the Control Display offers a choice of various functions for which the button can be programd, such as Zoom for the navigation system or Headlamp wash.
Those functions are selected from the Control Display using the controller. The button is then assigned the selected function. Different drivers can assign different functions to the button.

Steering wheel adjuster button

The steering wheel is adjusted by means of the button on the left-hand side of the steering column trim.

Semi-electrical steering wheel adjustment: press steering wheel adjustment button. An electric motor releases the steering column lock for five seconds.
Within that period, the driver can adjust the position of the steering wheel manually as required.
After five seconds, the steering column is automatically locked in position again.
If the period of five seconds is too long for the driver, the steering column can be locked immediately by pressing the button again.
Fully electrical steering wheel adjustment (”Electrically adjustable steering wheel” option) The steering wheel position is adjusted electrically by means of a button. The adjuster button has four possible directions of movement. These enable the steering wheel to be moved up, down, forwards or backwards.
The choice of steering wheel position is a Car&Key Memory function. It is memorized together with the driver's seat position.
When the ignition is switched off and the door contact signals ”open”, the steering wheel is moved to its highest and most forward position so as to make getting in and out of the car easier.

Fanfare horns

The fanfare horns serve both as a warning signal and as redundant-system audible antitheft alarms.

The directly read horn switch signal is sent as a valid status via the steering wheel module and the coil spring conductor to the steering column module (control module of the steering column control center). The steering column module can control the high-tone and low-tone horns separately. The power consumption for each horn is approx. 5 A.

Steering wheel heater

The steering wheel heating system consists of

a button on the left of the steering column for switching the steering wheel heater on and off
a function indicator in the steering wheel heater switch which lights up when the steering wheel heater is on.
the heater coil in the steering wheel rim which heats up the steering wheel
a temperature sensor in the steering wheel rim which sends the temperature signal back to the steering column module.

The SZL (steering column control center module) activates the heater coil as required in order to ensure even heating of the steering wheel.

Control modules

The following control modules are involved in the message transmission for the SZL:

SZL (steering column switch center): the steering column switch center processes all the data of the multifunction steering wheel. The SZL transmits the data across the BYTEFLIGHT bus to the ZGM.
ZGM (Central Gateway Module): The central gateway module provides the link to the bus systems. The ZGM sends the data to each receiver control module: wiper module, rain/driving light sensor, EGS, DME, KOMBI, LM.

For safety reasons, there are two serial cable connections in addition to the bus connection:

From the SZL to the LM (light module) and
from the SZL to the EGS (Electronic Transmission Control).

Service functions

Note on safety

For all work on the steering column switch center, comply with the safety legislation for work on airbags!

Disconnect battery!

Country-specific version

USA: Emergency release for electronic parking lock with remote control only

In an emergency, the electronic parking lock be unlocked mechanically: Undo the cover in the footwell on the driver's side at the left-hand A-pillar.

On USA models, the cover can only be opened with the remote control. This ensures that unauthorized persons are unable to release the electronic parking lock manually.