The comfort start enables operator-friendly start of the engine, as the starter motor automatically remains on until the engine is running.
The immobiliser ensures that an engine start-up is only possible when a remote control belonging to the car or the spare key (in the key adapter) is inserted in the ignition lock.
The Car Access System (CAS) control unit contains the functions of the radio remote control, the ignition switch, the terminal control, the immobiliser and the starter motor control. It is also the gateway module between the data buses K-CAN SYSTEM and K-CAN PERIPHERALS.
The start-stop button and the ignition lock are integrated in the CAS.
In addition, the CAS contains the data for the EWS random code (EWS: electronic vehicle immobilization system) that is sent to the engine control unit on starting up.
The CAS controls terminal 15 for all electrical systems. In addition, with terminal R on, the information ”Terminal R on” is transmitted via the data buses to the control units.
The CAS also activates terminal 15 wake-up for all control units of the PT CAN Activation of the terminal 15 WUP has the effect that the control units are shifted from sleep mode to operating mode.
In the starting process, terminal 50L for the comfort start relay and terminal 50E for the start request are switched to the engine control unit.
The remote control contains the data for the electronic vehicle immobilization system (EWS) and the radio remote control. An accumulator is integrated for the power supply. The accumulator is charged when the remote control is engaged in the ignition lock.
For mechanical emergency actuation in the case of failure of the central locking system, a mechanical key is inserted in the remote control. However, this mechanical key contains no EWS data.
As emergency key, a mechanical spare key is supplied; this also contains a data memory for the EWS data (transponder). The spare key can be inserted in the ignition lock in the CAS using an adapter.
The engine control unit controls and monitors all the functions of the engine. It also controls the ignition and the fuel injection.
The data for the EWS random code is also stored in the engine control unit. The EWS data is transmitted between the CAS and DME across the data line D_EWS.
The brake-light switch is an electronic switch that records operation of the brake pedal. Two switches are integrated in the switch housing: the actual brake-light switch and the brake-light test switch. This enables function monitoring of the switch.
An engine start-up is only possible when the brake pedal is pressed. For reasons of safety, the CAS control unit evaluates both the signal of the brake-light test switch and the switch signal across the data bus K-CAN SYSTEM.
The light module controls and monitors the vehicle lights. Information is received and sent via the data bus K-CAN SYSTEM.
The light module registers the signal of the brake-light switch and routes it across the data bus to other control units.
The DSC control unit contains the functions of the anti-lock braking system ABS and driving dynamics control. The DSC control unit is connected to the PT-CAN data bus.
When the brake is pressed, the DSC control unit sends a signal across the data bus to the effect that brake pressure has been set up. The CAS uses this information, which means that even if the brake-light switch fails an engine start-up is possible.
The EGS control unit controls and monitors the functions of the automatic transmission. It is connected to the PT-CAN data bus.
An engine start-up is only possible when the gearbox is in park position (selector-lever position P) or neutral position (selector-lever position N). The gearbox control unit transfers the selector-lever position across the data bus. For reasons of safety, there is also a line between the gearbox control unit and the CAS control unit (line name P). Positive (battery voltage) is switched across this line when the selector lever is at P or N.
The central gateway module links the data buses
The overall sequence for starting the engine can be described as follows:
The remote control is inserted in the ignition lock.
Pressing the start-stop button
When the start-stop button is pressed, terminal 15 is activated first of all.
When the start-stop button is pressed, the CAS checks whether the brake pedal is pressed and the gear selector lever is at P or N. If this condition is met, the engine is started:
Starter motor anti-repeat lock
The starter motor anti-repeat lock prevents activation of the starter motor when the engine is running. The anti-repeat lock is active as long as there is engine speed.
Emergency on function
The 'emergency on' function enables immediate restarting of the engine following an engine stop caused by incorrect operation; the need to press the brake pedal is eliminated. The requirement is that a the car road speed > 1 km/h.
If the start-stop button is pressed when the engine is running, the engine is stopped.
With engine shutdown, the automatic transmission is automatically shifted into the park position.
Following engine shutdown, the remote control can be removed from the ignition lock. To release the remote control from the mechanical locking, it must be pressed lightly into the lock. In the CAS, a Hall sensor (Eject switch) detects that ejection is required. When the engine and vehicle are at a standstill, the remote control is unlocked and can be removed from the ignition lock.
Removal lock
The remote control cannot be removed from the ignition lock while the engine is running or the vehicle is moving.
The function of the Electronic Vehicle Immobilization System (EWS) is integrated in the CAS control unit. The immobiliser ensures that an engine start-up is only possible when a remote control belonging to the car or the spare key is used.
A random code process ensures that all types of manipulation are excluded, for example electronic copying of a remote control.
Key identification
The data of 10 remote controls / spare key is stored in the CAS control unit. If a remote control or spare key is used, the identification code in the remote control and/or spare key is changed by means of a random code process.
New remote controls or spare keys must be ordered using the vehicle identification number (VIN).
Interface to DME
The drive-enable code is transferred across a line between the CAS control unit and the engine control unit. The engine control unit only enables the ignition and fuel injection when this code is recognised as valid.
The basic code (starting value) of the immobiliser is entered in the CAS on vehicle production and cannot be changed. It is transferred via a diagnosis command to the engine control unit if this is still unused. Following this entry, the starting value in the engine control unit can no longer be changed.
After every engine start, the drive-enable code in the CAS and in the engine control unit is changed on the basis of a random code process.
The following points must be borne in mind when the CAS or the engine control unit are replaced:
In the case of a new engine control unit, the service function ”DME/DDE - CAS matching” in the BMW diagnosis system is used to read the EWS drive-enable code from the CAS and transfer it into the engine control unit. This means that the engine control unit and the CAS control unit are mutually linked.
If the engine control unit is already linked to the CAS, the service function is used to perform a starting value match. This means that the random code calculation between the CAS and the engine control unit is matched.
A start match is required if there is a variance in the random codes caused by the influence of errors in the two control units.
The service function ”Disable remote control/spare key” in the BMW diagnosis system can be used to disable or enable remote controls or spare keys.
It is recommended that a key is disabled if it is lost or stolen. A disabled remote control (or spare key) is not locked in the ignition lock and the engine can therefore not be started. The functions of the radio remote control are also disabled.
A remote control or spare key can only be disabled if the remote control or spare key has been used at least once and it is currently not inserted in the ignition lock.
To run the service function, it is required that a valid and enabled remote control or valid and enabled spare key is detected in the ignition lock.
Insert the new remote control in the ignition lock and hold in this position until the remote control locks into place. This can take up to ten seconds. After locking, wait another five seconds. The remote control is then ready for use.
If the remote control is a replacement for a lost or defective remote control, the old remote control still has to be blocked using the service function ”block/release” (see above). To use the Car/Key functions, the service function ”Personalization number” has to be run.