Body Control Module: Description and Operation
Electronic Vehicle Module (EKM):
Functional Description:
General:
The electronic vehicle module (EKM) processes the signals of a large number of sensors and control units. The information and messages are displayed via the
Instrument cluster:
and-
Multi-information display (MID):
The EKM calculates all values to be indicated/displayed (exception: tD signal for tachometer connected directly to instrument cluster) and transfers the data via two separate data links to the instrument cluster and the MID.
Instrument Cluster:
The following functions are detected by the EKM and displayed in the instrument cluster:
- Position signal for speedometer and odometer
- Coolant temperature
- Tank content measurement
- Hand brake warning lamp
- Seat belt indicator lamp (USA only)
- Brake fluid level/brake pressure warning lamp
- CC indicator lamp
- Gear and program display (EGS transmission)
Engine speed measurement:
The to signal (engine speed signal) for the tachometer is connected directly at the instrument cluster. The to signal connected at the EKM is only used as part of the check control function.
Tank content measurement:
The tank contents are measured by way of two lever-type sensors which are connected in series. Since the measured value of the sensors fluctuates considerably when driving at high speeds, in order to improve display accuracy, the consumption is additionally calculated on the basis of the ti signal (injection signal) and then subtracted from the tank contents last measured. As soon as the measured value of the lever-type sensor is sufficiently accurate once again (e.g. steady driving or when stationary), a balance takes place between the calculated and measured tank contents.
No reserve contact is provided for the reserve lamp. On the basis of the tank content measurement/calculation, the lamp is switched on at a reserve content of approx. 10 lit..
Data transfer:
The EKM transfers the data to the instrument cluster via a separate data link. This data link (serial interface) to the instrument cluster is independent of the I-bus (instrument bus).
Multi-information Display (MID):
The following functions are detected by the EKM and displayed by the multi-information display (MID):
On-board computer functions:
- Clock/date
- Timer for independent heating/ventilation or stopwatch
- Average consumption (derived from ti signal from DME I and II and position signal)
- Outside temperature
- Average speed
- Distance entry and calculation of expected time of arrival
- Calculation of range referred to tank contents
- Entry of limit speed
- Entry of a code number for drive-away protection/antitheft
Code number:
After entering a code number in the MID, the drive-away protection and antitheft function is active. The front lid and the radio are monitored as part of the antitheft system. The alarm horn is activated in the event of unauthorized intervention.
The EKM switches a B+ signal to the DME I and II for as long as the drive-away protection function is active. The engine can not be started before the correct code number has been entered after switching on the ignition.
Entering the code number:
- Ignition switch in terminal R setting
- Enter code number in MID, acknowledge entry with setters
- The drive-away protection/antitheft function is active when terminal R is switched off
Disarming the system:
- Switch on ignition
- Enter code number in MID, acknowledge entry with Set/Res
The alarm horn is activated after three incorrect entries For measures to be taken when the code number has been forgotten, refer to Multi information display (troubleshooting!)
Check-control messages:
The EKM processes the signals of a large number of sensors and control units. If a defect occurs, the Driver is informed by way of a text message. This text is shown in the MID. In addition, the CC indicator lamp is switched on in the instrument cluster.
Data transfer:
The EKM transfers the data to the multi-information display via the I-bus (instrument bus).
Outputs at the EKM:
The EKM controls the following outputs:
- 3 acoustic outputs for acoustic generator (gong). The acoustic generator can be activated with different frequencies.
- Speed signal output to DWA. Position signals sent to DWA when vehicle is pushed.
- Alarm to DWA. A relay switched in the DWA control unit.
- Start blocking to DME III when a code number (drive-away protection) is entered at the MID.
- Switching on the independent heating/independent ventilation after entry of a switch-on time at the MID.
- Speed A signal. Position signal for other control units.
I-Bus (Instrument Bus):
The instrument bus (I-bus) is a data link, to which a large number of control units are connected. The control units can exchange data with the EKM via This data link. The EKM controls and monitors the entire data flow on the I-bus.
Examples:
- The ZKE (central body electronics) signals to the EKM the status of the passenger S door and rear lid (open/closed) via the I-bus.
Central Control Module
- The LKM ([1][2]lamp control module) signals to the EKM the status of the lamps (OK/not OK) via the I-bus.
- The EKM sends the current time to the MID.
In the *D* diagnostic program, an inquiry can be made under the selection "special functions - coding data" as to which control units are connected to the
I-bus.
Control units connected to the I-bus. In addition to ZKE, LKM and MID, other control units can also be connected.
Diagnostic mode of I-bus users:
Diagnostic mode between the BMW Service Tester/MODIC and control units which are connected to the I-bus (e.g. LKM, ZKE, MID) takes place via the I-bus. The diagnostic links RXD and TXD are connected to the EKM.
Example:
Example of the diagnostic procedure with ZKE
- BMW Service Tester sends a diagnosis command to the ZKE, e.g. read defect code memory.
- The command is sent via the RXD link to the EKM.
- The EKM receives the command and recognizes by way of a control word that the command concerns the ZKE.
- The EKM transfers the command via the I-bus to the ZKE.
- The ZKE receives the command and performs the instruction; e.g. the contents of the defect code memory are sent via the I-bus to the EKM.
- The EKM receives the data from the ZKE and transfers them via the TxD link to the BMW Service Tester.
Diagnostic mode via EKM:
In order to reduce the number of plug-and-socket connections, the diagnostic links RxD and TxD are looped through in the EKM. A large number of control numbers are therefore connected to the EKM.
Check Control:
The check control is a comprehensive system of messages which inform the driver about various statuses in the vehicle. The display is in the form of a text message in the multi-information display (MID) and is accompanied by an acoustic signal (gong). The CC indicator lamp additionally lights in the instrument cluster.
The EKM detects the statuses:
- via sensors connected to the EKM,
- via control units which are connected to the I-bus and signal defects within their function range to the EKM. e.g. the [1][2]lamp control module (LKM) monitors the lighting.
Priority groups:
The CC messages are subdivided into three priority groups.
Priority 1:
Faults which directly endanger driving safety. Indicated by flashing arrows in the display. The message, as well as the CC indicator lamp cannot be cleared.
Priority 2:
Faults which do not directly endanger driving safety. The message text can be deleted, however, it is cleared automatically after approx 2 minutes. After being cleared indicator arrows signal that a message is still pending.
Priority 3:
Messages relating to fluid levels, "light ON" warning, seat belt They are indicated only when the ignition is switched on and off and are cleared after approx. 2 minutes.
The messages of a large number of sensors and control units are processed by the EKM. Check control messages are displayed in the MID.
Clearing and calling messages:
Priority 2 and 3 messages can be cleared with the "CHECK" key on the multi-information display (MID).
It several messages are pending at the same time, they can be selected by way of This "CHECK" key. A cleared priority 2 message can be recalled.
Languages:
The language of the CC message texts is programmed in the EKM. It can be changed by taking corresponding measures at the MID.
Coding Data:
All coding data for the EKM and instrument cluster are stored in both control units.
Replacement of a control unit:
If one of the two control units is replaced, immediately after switching on terminal R, the coding data are transferred to the new control unit.
The data exchange lasts approx. 10 seconds. During This period of time, there is no distance display in the instrument cluster. Also in the MID, no message and no time are indicated during This data exchange period.
Data exchange does not take place if a used control unit is installed (e.g. EKM from another vehicle).
Note: All *D* diagnostic functions and the instrument cluster system test are also possible when data exchange has not taken place.
Test mode of a control unit and used identifier:
A new EKM or instrument cluster can be installed in a vehicle for test purposes. After data transfer, a counter is activated which counts the operating hours, i.e. operation with terminal R switched on.
After 8 hours of operation, an identifier is stored, indicating that the in- stalled control units are "used". The data are now permanently stored and can no longer be overwritten.
However, identification does not take place if the control unit is removed once again before the 8 hours of operation have elapsed. The control unit can once again be installed in another vehicle. The data contained in the control unit are then overwritten by new data. The operating hours counter is reset to zero when the EKM is removed.
*D* control unit identification of EKM and instrument cluster shows whether the control units are "used" or in the "test phase".
Error messages:
The following messages can be displayed in the display unit of the instrument cluster (field for trip odometer):
EEEE: Instrument cluster and EKM from different vehicles, therefore data exchange not possible.
PPPP: EKM and instrument cluster not coded or faulty data record in EKM. Record EKM.
Note:
If the EKM is renewed, during automatic data exchange, EEEE or PPPP are indicated for 10 seconds depending on whether the installed EKM is uncoded (EEEE) or coded PPPP).