Electronic ignition switch control unit, task - GF80.57-P-4102-03PP

The purposes of the EIS control unit (N73) are as follows: 

• Check and control of access authorization
• Check and control of drive authorization
• Infrared communication with the transmitter key (A8/1) when inserted and inductive energy transmission to the transmitter key (A8/1)

Gateway function 

The EIS control unit (N73) serves as the interface (Gateway) between the Control Area Network bus, class B (interior compartment) (CAN B) and the Control Area Network bus, class C (engine compartment) (CAN C) for interchange of data between the two bus systems.

Diagnosis function 

The EIS control unit (N73) provides the connection between the CAN B control modules and the diagnostic test connector (X11/4).

Shiftlock function (with transmission 722) 

The mechanical shift lock function prevents the transmitter key (A8/1) from being turned back to the "0" position when the shift lever is not in the "P" position.

Code equipment versions 

The equipment versions are coded in the EIS control unit (N73).

Provision of circuit: 

• C. 15C on CAN B
• C. 15R on CAN B and as hardware output
• C. 15 on CAN B, CAN C and as hardware output
• C. 15X on CAN B (c. 15X serves for switching off loads during the starting operation. C. 15X is ON, when the engine is running stably or when c. 15 is ON and an attempt is not being made or has not been made to start the engine.
• C. 50 on CAN Band CAN C

Scan the following switches: 

• Combination switch (S4)
• SBS switch (S93/2) (on together with steering column adjustment lock indicator switch (S97/1))
• (on models 203.0/2/7) TPM button switch with variable speed limitation (S40/4) (on model 209) TPM button switch (S40/4)
• Left multifunction steering wheel button group (S110)
• Right multifunction steering wheel button group (S111)

Read in button for multifunction steering wheel 

The left multifunction steering wheel button group (S110) and right multifunction steering wheel button group (S111) are read in by the EIS control unit (N73). voltage-coded.

Observe the following peculiarities:

The left multifunction steering wheel button group (S110) and right multifunction steering wheel button group (S111) are read in directly by the EIS control unit (N73) over two leads only. If the voltage coding for the various button functions was accomplished here only with various resistors with corresponding incrementation, the resistance to interference would not be sufficient.

• The voltage generated by the EIS control unit (N73) for scanning the left multifunction steering wheel button group (S110) and right multifunction steering wheel button group (S111) changes its polarity continuously.
• In each case, a diode is connected in series to the left multifunction steering wheel button group (S110) and right multifunction steering wheel button group (S111) whose polarity differs for the two groups.
• The left multifunction steering wheel button group (S110) or right multifunction steering wheel button group (S 111) are checked alternatively depending on the polarity of the scanning voltage from the EIS control unit (N73). The button check "switches" back and forth between the two groups of switches. Actual voltage coding is therefore accomplished only within the left multifunction steering wheel button group (S110) or right multifunction steering wheel button group (S111).

Assessment:

If a number of buttons are actuated simultaneously within the left multifunction steering wheel button group (S110) or right multifunction steering wheel button group (S111), only one function is activated by the EIS control unit (N73) in each case.

This results in different priorities for the various functions within the left multifunction steering wheel button group (S110) or right multifunction steering wheel button group (S111). The button with the lowest resistance has the highest priority.