How does a diagnose interference work (MB SD C4)

[bmw318isblack]

Hello friends,


i am not from the car industry and too stupid to understand how a diagnose interface works.
Lets take the MB SD C4 for an example, you have the can bus and k-line communication.

As i understand for



1. can communication the data coming from OBD2 interface going direct to CAN transceiver and then to MPU, like this:
CAR <> OBD2 interface <> CAN transceiver <> MPU (no relais or multiplexer needed)


2. K LINE

CAR <> OBD2 interface <> relais <> multiplexer <> MPU



Is this how its work or did i get it wrong and can i read it up somewhere?



I hope someone can help me, that way i don't have to die stupid ^^
B.

[bmw318isblack]

Especially for what do you need relais AND a mux ic?


B.

[autotrans]

Not a bad description , just a few points there are several types of can, hi speed / medium / lo / single wire.
Most vehicles use hi speed for engine / transmission / abs ect. the other types for less important E C U s
As for the k line, merc's use a multiplexer but most manufacturer's use a different target address for each E C U.

[bmw318isblack]

Thank you for the fast answer, what for me is very interesting is the part for what the relais are used and how the MUX is integrated in this (with DeMux and Mux the messages)?
I think you have via OBD2 interface only 2 lines for K-LINE, somehow you need to decode that information.

Thx
B.

[autotrans]

Mercedes k line use different pins in the obd connector for different E C U's
change over relays are used to access these pins.
example early A class
pin
engine 7
transmission 11
selector 12
esp abs 9
instruments 15

[bmw318isblack]

Thanks for your help autotrans, slowly i understand ^^.

B.