The EMLIIIS control unit transmits and receives signals from other control units or components both in digital as well as in analog form.
Digital data transfer takes place via the CAN-bus between the control units, analog data transfer takes place to the brake switch, kick-down switch and fault indication in the instrument cluster.
Communication between the EMLIIIS control unit and the control units AGS, both DMEs and DSC takes place via the CAN-bus, facilitating extensive data exchange on digital level. The only exception to this is the safety fuel cutout signal from the EMLIIIS control unit to both DME control units which is transferred via the external safety path.
For this purpose, a CAN-module is installed in the EMLIIIS control unit and in the other control units which are interconnected via a star coupler, to which shielded supply lines lead from each control unit with a total line resistance of 60 Ohm. This is achieved in that the terminal resistor in the DSC control unit (fixed to 120 Ohm) and in the AGS control unit (120 Ohm, activated by a jumper) are connected in parallel.
By way of self-diagnosis, the EMLIIIS control unit constantly checks both for correct transmission and reception of messages on the CAN-bus as well as identical CAN status of all control units.
Note
Particular care must be taken when replacing one of the CAN-bus control units to ensure the identical CAN status otherwise communication via the CAN-bus will not be possible. Check by means of diagnosis program on identification page under "Bus index".
An electronic brake switch is installed in both series E31 and E38, in that 2 brake switches are accommodated in one housing. The function of the electronic brake switch is checked by the self-diagnosis function every time the brake is operated.
In E31 vehicles the electronics simulates the switching characteristics of the 2 mechanical brake switches of the previous EML system, which switch slightly offset. The first switch (BLS signal) is a make contact, i.e. during operation it closes to U-batt and transfers this signal to the external safety path. The slightly delayed second switch (BTS signal) is also a make contact which, however, when operated closes to ground and transfers this signal to the EMLIIIS control unit.
In E38 vehicles, the two brake switches switch at the same time exactly. The one switch (B-EML signal) is a make contact, i.e. when operated it closes to U-batt and transfers this signal to the external safety path. The second switch (BL-ON signal) is a break contact, i.e. when operated it opens from ground and transfers this signal to the EMLIIIS control unit.
The kick-down switch is used to activate the downshift procedure in automatic transmissions. This switch is used in all series E31 and E38 vehicles with 12-cylinder engine M73B54 since these vehicles are equipped solely with automatic transmission.
The kick-down switch in both series E31 and E38 is a make contact, i.e. when operated it closes to ground.
The task of fault indication is to inform the driver of a fault in the EMLIIIS system which can lead to limitations in output or to deactivation of various functions, and is intended to draw the driver's attention to a necessary workshop visit.
In E31 vehicles, a fault is indicated in the form of a warning lamp with the inscription "EML" in the instrument cluster.
In E38 vehicles, a fault is indicated by way of a "engine emergency program" message in the check-control module of the instrument cluster.
Note
The ignition must be switched off for approx. 10 seconds after clearing the defect code memory of the EMLIIIS control unit. The fault indication is then deactivated when the ignition is switched on again.