Help with reading ABS/Airbag DTCs over elm327

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Help with reading ABS/Airbag DTCs over elm327

Postby Arnaud » Sat Jan 06, 2018 11:32 am

Hi everyone,

Sorry if I'm being unclear or posting in the wrong place.
I searched a lot and tried my best to pick the right section beforehand.
I'm new to this whole universe and still need to learn a lot about it, so I might still have missed something.

We are a tiny 2 people software startup and we need our app to fetch DTC codes from our elm327-based reader.
We have no issue fetching engine related DTCs. But we don't get Airbag or ABS codes.

After a full day of googling, it's my understanding that we need to address those modules directly by setting some special headers on the ELM to get answer from them.
I could dig out that for GM vehicles, "AT SH 6C 58 F1" would allow me to talk to the Airbag ECU for instance.

We need to support all main suppliers for the US market.

Is there any place any where where I could find a consolidated list of those addresses? How different is it across manufacturer?
Where can I find which command to send in each case to get the codes?
Any advice on how I should proceed to achieve our goal? Any place I should look at? Any reference documentation anywhere?

Thanks a lot,
-- Arnaud

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Re: Help with reading ABS/Airbag DTCs over elm327

Postby antus » Sat Jan 06, 2018 12:59 pm

It is different across manufacturers, and across differing data busses on different pins for different vehicles. Sometimes there is extra comms to get your packets through an extra module such as a BCM. ELM interfaces are also not created equal. To do this you'd need to spend big $ and subscribe to one of the vendors who re-sell such data, but its $thousands and I cant remember the name of the group now. Enough googling and you should be able to find them if you're willing to great lengths to get this working. It wont be easy. It also looks like your talking vpw/pwm protocol which wont cover can bus/kwp. Most holdens that are vpw have most modules including SRS on ALDL which the elm does not support.

Your best realistic bet would be to find a tool that does what you want (if one exists) and reverse engineer the traffic on the vehicle data bus.
Have you read the FAQ? For lots of information and links to significant threads see here: viewtopic.php?f=7&t=1396

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Re: Help with reading ABS/Airbag DTCs over elm327

Postby Arnaud » Sat Jan 06, 2018 1:04 pm

Thanks for the info antus, this is helpful!
If anyone has any clue as to which vendor we can contact to purchase this data I'd be interested to know more as this is critical to our product.
Thanks for clarifying all this.
Just to make sure I understood what you said: It should be possible with the ELM to talk to ABS/Airbag module on CAN systems but often won't be on VPW ones?
Reverse engineering the traffic with an existing tool would be doable to support one vehicle in particular but I can't really reverse engineer each vehicle class one by one.
Cheers
-- Arnaud

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Re: Help with reading ABS/Airbag DTCs over elm327

Postby antus » Sat Jan 06, 2018 1:11 pm

No that is not what I mean. It wont be possible on vehicles where it is on the ALDL data bus (many up to mid 2000's holden/gm including most which use VPW for engine comms because of re-use/certification/testing etc they still have most modules on ALDL).

The data source I'm thinking of is https://www.etools.org/TEK-NETLibraryOEMData

Ive never used them, just wanted access to the data. But it was prohibitively expensive for me.
Have you read the FAQ? For lots of information and links to significant threads see here: viewtopic.php?f=7&t=1396

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Re: Help with reading ABS/Airbag DTCs over elm327

Postby Tazzi » Sat Jan 06, 2018 2:41 pm

50k on GMs. Ohhhhh yeah, expensive is an understatement.

Arnaud, I wouldnt recommend trying to use an ELM. They are not really intended for any complex tasks. Iv been down this road, made software for the ELMs, and basically had to do alot of little 'tricks' to get the ELM to do things its not designed for so it could read Holden specific live data and faults ect.

The ELM is better for use with smartphones, or other devices which are generally made to look 'fancy', but realistically dont provide alot of actual useful info.

Youd go better to find a more comprehensive tool, as in the end it will be more durable and easier to develop with.

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