J1850 VPW functional messages

They go by many names, P01, P59, VPW, '0411 etc . Circa 1999 to 2006. All VPW OBD2 PCMs.
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J1850 VPW functional messages

Postby pman92 » Thu Jun 18, 2020 9:28 pm

Hi guys,

I've been playing around looking at the VPW databus recently and trying to understand whats happening on it.

I've got an LS1 PCM and a PIM (which aren't linked, they are random units from random cars) connected up on the bench and I'm watching the data on the bus when I turn ignition on. There's around 70 frames sent within the first second of ignition on with just these 2 modules connected, and from then on it quietens down and there is only a couple of frames per second.

I've found this very useful website: https://www.fastfieros.com/tech/vpw_com ... otocol.htm and also found a PDF containing alot of J2190 information which all seems to make sense (at least from my brief look), but it seems to only cover PHYSICAL frames (when bit 2 of the header byte is set). I can't seem to find any information on FUNCTIONAL frames apart from the J1979 mode $01-$09 stuff.

Of the roughly 70 frames in the first second, only 2 are physically addressed. All the rest are functional.
I've noticed all the functionally addressed frames have a destination byte that is different / doesn't correspond to any physical node (obviously because its a functional address), but the source address byte is still the same physical node ID.

Is there any information on understanding all these functional frames? Is there an SAE document I'm missing? Or is it all proprietary GM stuff that isn't defined by any standard?

Thanks in advance
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Re: J1850 VPW functional messages

Postby picvrss » Thu Jun 18, 2020 10:37 pm

You'll find descriptions of the functional message format in J2178-2 Data Parameter Definitions, and J2178-4 Message Definitions for three-byte headers.

Google "J2178-2 baidu" and "J2178-4 baidu".

I needed these when I designed a manual paddle shift module for my son's VZ SV8. An example of the messages I use are shown below, and you'll recognise these on your VPW logger:

; Functionally addressed message format (hex notation)
; "HH", "LL" and "XX" are variable hex values. CRC is Checksum
;
;RPM:
;88 1B 10 10 HH LL CRC
;
;SPEED:
;88 29 10 01 XX CRC
;
;CURRENT GEAR:
;88 3B 10 03 XX CRC
;
;PRNDL:
;68 EA 10 0A XX CRC

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Re: J1850 VPW functional messages

Postby In-Tech » Sat Jul 11, 2020 6:07 pm

Hello,
I googled the baidu j2178-1,2,3,4 stuff and didn't see how to download the files. Do you guys have those saved and can forward? I was hoping to find J2190_200810 pdf too.
Thanks

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Re: J1850 VPW functional messages

Postby picvrss » Sat Jul 11, 2020 8:04 pm

Hello In-Tech,

Yeah, they're a bit of a struggle to download.

Actually, you don't really download as such. I took a snip of each page after translating and finding the green button that displays the next page - very tedious.

I've done all the hard work and have the files, but I'm not too comfortable with the whole copyright thing and public posting.

Can anyone advise me on this point? Happy to post the files if there are no comebacks.

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Re: J1850 VPW functional messages

Postby In-Tech » Sat Jul 11, 2020 8:34 pm

Hello and thanks for the reply,
It's up to the site owner(s) about posting it, totally understand the whole copyright thing.

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Re: J1850 VPW functional messages

Postby antus » Mon Jul 13, 2020 6:54 pm

Ok, well site owner is me, so I'll be clear. It is important that the site does not contain any copyrighted material posted without permission. If the documents are not labeled as copyright and you want to post them please go ahead, but dont remove copyright tags to game the system. If any copyright holders see this and need content removed, please contact me and provide details and I will assist. I believe small snippets should be OK for educational purposes and references but lets keep that to a minimum. Sorry it has to be that way, but I think its better for everyone in the long run.
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: J1850 VPW functional messages

Postby antus » Mon Jul 13, 2020 7:06 pm

@In-Tech, Im not sure you do want that document, it looks like it was cancelled and the 1993 revision updated instead https://www.sae.org/standards/content/j2190_200810/
Having said that I dont know what cancelled means, Ive not seen it before on other SAE docs.
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: J1850 VPW functional messages

Postby picvrss » Mon Jul 13, 2020 8:21 pm

Thanks for the policy clarification, Antus; it’s exactly the reason I asked.

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Re: J1850 VPW functional messages

Postby In-Tech » Mon Jul 13, 2020 10:47 pm

Thanks guys,
I saw that one was cancelled and was just wondering if it had anything newer in it compared to the '93 one. I think it's ~$83usd at sae.org and I've got plenty of other crapola to read and study in the meantime :typist:

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Re: J1850 VPW functional messages

Postby Gampy » Mon Jul 13, 2020 11:06 pm

To state the obvious ...

The fact they are trying to sell it implies they don't want it posted for free!
I'm not angry, I'm a brash, blatant, driven, passionate individual that is extremely intense!

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