Transmission Selector Switch/Control Buttons
ISIS SZL Steering Column Switch Center
The functional range of the SZL can be divided into three main blocks:
- SZL as an ISIS satellite with connection to the BYTEFLIGHT bus (ISIS is the Intelligent Safety Integration System)
- SZL as switching center for the control functions on the steering wheel and steering column
- SZL as steering-angle sensor.
In the steering column switch center, the following functions can be operated quickly and ergonomically by the driver:
- 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, windscreen wipers, cruise control -> via the 4 control levers on the steering column
- partial and/or fully electric steering column adjustment -> button on the left-hand side of the steering column
- steering wheel heating -> via the button on the left of the steering column.
Brief component description for EGS function (Electronic Transmission Control)
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-angle sensor in the steering column
- Control module SZL (Steering Column Switch Center Satellite)
The electronic control for the steering column switch center is divided into two electronic modules:
- Electronic modules integrated in the steering column
- Electronic modules integrated in the steering wheel
The signal transfer from the control elements in the Multifunction Steering Wheel (MFL) is ensured by a coil spring.
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 sensors 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
Information displayed to the driver
- Gear shift pattern in the gear selector lever: the gear shift pattern is equipped with a locating light (dependent on terminal 58 g).
- 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 control module (Electronic Transmission Control).
Signal path: From SZL (Steering Column Switch Cluster) -> data bus BYTEFLIGHT -> SIM (Safety Information Module) -> data bus BYTEFLIGHT -> ZGM (Central Gateway Module) -> data bus PT-CAN -> EGS (Electronic Transmission Control).
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 anti-theft measure: the electronic parking lock replaces the steering column lock.
Electronic parking lock emergency unlock: In an emergency, the electronic parking lock be unlocked mechanically:
- Undo the cover (Phillips screw) in the footwell on the driver's side at the left-hand A-pillar.
- Unlock the electronic parking lock manually.
Steering-column lever, bottom left: Cruise control
The steering-column lever for cruise control increases or reduces the traveling speed.
The cruise-control system comes with the special equipment "ACC, Adaptive Cruise Control".
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. frequently required speeds, such as 30 km/h, 50 km/h, 60 km/h. For these required speeds, speed marks can be set and stored.
Programming required speeds: It is best to program required speeds with the vehicle 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 lever, the axial one-touch button or the rotary actuator (in the case of "ACC, Adaptive Cruise Control" as special equipment), a message is sent to the DME/DDE or the ACC control module.
Signal path: From SZL (Steering Column Switch Cluster) -> data bus BYTEFLIGHT -> SIM (Safety Information Module) -> data bus BYTEFLIGHT -> ZGM (Central Gateway Module) -> data bus PT-CAN -> DME/DDE or ACC.
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.
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.
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 unlocking of the electronic parking lock only with identifier
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.
In the USA, the cover can only be removed with the identifier. This ensures that unauthorized persons are unable to release the electronic parking lock manually.