Airbag ECU - Connection Possible outside of Vehicle?

[jbourne99]

I'm experimenting with the possibility of using an airbag module from an E39 (5er) in my 2000 E36/7 (Z3).

The airbag modules have the same pin-outs except for the following differences:
* extra sensors and airbags in the E39
* k-bus data line in E39 where the E36/7 has a d-bus connection.

I believe that one of the parameters that can be coded to the airbag module include which bus connection to use (k vs d).

If I put this E39 airbag ECU (uses K-BUS) in my car which uses D-BUS I'm not sure I'll be able to program it and I'm worried it will cause trouble in my system or fire an internal fault that can't be cleared.

I'm wondering if there is anyone who knows how to directly connect their K+DCAN cable or other cable to the airbag ECU.

I already tried having my d-bus airbag module outside of my car with the following lines hooked up:
* power supply providing 12.5V DC
* ground from power supply
* d-bus line hooked up to the d-bus line of my KD-Can cable.

I wasn't able to communicate with the module using INPA but had no problems communicating with it when it was inside my car.

Please, what am I missing??

[jbourne99]

Update. I got a PM informing me that the "Z3 uses the standard K-line to communicate with airbag module. Often BMW wiring diagrams will call this TxD, but it's a normal K-line."

Maybe communication will be possible. Whether or not it is a good idea to put a different models airbag module in my car is probably not a smart idea because we don't know the internal differences in them.

[gpeterson]

The cluster translates k-bus messages to d-bus (yes, they are different). You could wire up a cluster or change your ediabas.ini to use Interface = KBUS instead of Interface = STD:OBD.

[jbourne99]

Thanks for that idea. I'll possibly be looking into it. If I do and make progress I'll post an update here.

Most recently I've learned that Carprog can interface directly with these units by wiring to the interface of the unit but just my luck the only one that requires soldering wires directly to the board is my airbag ECU, the Temic MRSZ3...

[328 Power 04]

The facelift Z3 airbag module (all of Z3 for that matter) doesn't use cluster as a gateway, so all K-line modules are connected together on their lines.
DME and EGS on 1 k-line, and the rest on the other k-line.

[jbourne99]

I did some experiments to see how I should try to communicate with the 5er airbag module xxx789 I received recently so I did the following with my original Z3 airbag ECU.
* remove the pins 5,6,9 (power, ground, TXD) from the airbag wiring harness
* plug these pins only directly into their position in airbag ecu

Results:
* I could communicate via INPA with airbag ECU normally
* I could communicate via PA Soft 1.4 with airbag ECU normally

I did this so I could try connecting to the 5er airbag ecu without connecting all the airbag circuits.

So I connected the 5er airbag ecu as above and got the following results:
* no communication with INPA "airbag" module in Z3 menu or E39 airbag menu items
* no discovery of "airbag" module when using "special" function of INPA that queries all active modules
* PA Soft 1.4 "scan" function says no SRS module present.

The next thing I'll try is gpeterson's suggestion below

... change your ediabas.ini to use Interface = KBUS instead of Interface = STD:OBD.

In ISTAD I think the module was showing up in the "tree" view of all modules but it had some hex code to it and it wasn't identified as a SRS module so maybe there is some kind of communication going on? I'm in the process of getting ISTAP to work to see if there are any programming options for it.

Thanks for any help for what could possibly could be the first MRS4 install in a 2000 Z3??

[jbourne99]

The cluster translates k-bus messages to d-bus (yes, they are different). You could wire up a cluster or change your ediabas.ini to use Interface = KBUS instead of Interface = STD:OBD.

Got home and trying to bench test the SRS modules. As a proof of concept I was able to hook up my Z3 SRS module (uses TXD line for communication/programming) directly to my K-DCAN adapter and use Tool32 to execute commands with success.

I don't have a cluster to wire up so I'm heeding your advice and trying to use ediabas to communicate directly with the 5 series SRS module which sits on the KBUS.

So the pin out for the 5-series SRS module is the same with respect to voltage, ground, and comm line. Wiring it up as such and not changing ediabas there was no success as expected with message "IFH-0009 No response from controlunit." . I tried to modify my Ediabas 7.3.0 (working on Windows x64 without problems) to communicate on the kbus by editing the OBD.INI file (the one my system uses is in the ediabas/bin directory -- there is none in the windows directory) by adding "MODE=KBUS". When attempting to communicate with the 5-series SRS module I get the error "IFH-0009 No response from controlunit." Just to verify that something is happening I re-hooked up my z3 srs control module and I couldn't communicate with it (as expected) with the "MODE=KBUS" setting giving me the same error message.

My power supply voltage is 12.5 V. The K-bus line on the 5 series SRS computer is 12.1 V. The TXD line on my Z3 SRS computer is 12.16 V.

I'm really at a loss regarding how to proceed from here regarding getting bench communication with the 5-series SRS module. It is always possible that the control unit I bought off ebay is a dud but this module was known to be pretty reliable.

I also have PA soft / BMW Scanner 1.4.0 so if there is a way to enable KBUS communication on that I could do it.

Thanks in advance for any help!

[jbourne99]

Using Ediabas 7.3.0 as well as an earlier version with Tool32 in KBUS mode as described earlier with an without a a "pull up resistor" didn't help in me communicating with the 5er airbag computer on the bench. I bought a CarProg clone off ebay around $50 with more connectors for it than I know what I'll ever do with but I was able to connect this up to the 5er airbag controller and read the eeprom and errors and can at least verify that the airbag controller isn't a dud. I'm giving up trying to communicate further with this airbag computer since I fixed my z3 airbag computer anyways. I'll plan on making a separate post on the details of this.