Switches for turning on/off J1850 VPW information

They go by many names, P01, P59, VPW, '0411 etc. Also covering E38 and newer here.
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Switches for turning on/off J1850 VPW information

Postby RADustin » Wed Apr 13, 2022 2:54 am

Gents,

I'd like to switch on the PCMs broadcast of ignition voltage over the J1850 bus to the gauge cluster. End goal being 03+ cluster/P59 in an original P01 truck, aka bcm is older.

Working with a P59 and ...618 OS(2005). Using a kodiak system segment I've already confirmed it's possible, but the full segment causes several undesirables as well-> including a security light which makes sense since kodiak has no security.

Looks like the ID for voltage is $1141. But I'm not sure if this is the broadcast ID or only if a scan tool requests.

Just looking to see if there is any knowledge on this stuff before I dive in to the hex and try to spot the location(s) of the switch/data that control it.

Thanks

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Re: Switches for turning on/off J1850 VPW information

Postby kur4o » Wed Apr 13, 2022 3:14 am

We need to make some logs and define the exact message that is send from pcm to cluster. Than some digging can be done to identify settings in bin.

For some playing around with bus you can check this program.

https://pcmhacking.net/forums/viewtopic.php?f=42&t=7753

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Re: Switches for turning on/off J1850 VPW information

Postby RADustin » Wed Apr 13, 2022 3:42 am

sweet I'll get that fired up.

as a means of brute force, I also cut the bin differences into 3 'trials'. Will try those to quickly funnel the search.

I don't think it'll take long. There isn't that much data to process.

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Re: Switches for turning on/off J1850 VPW information

Postby RADustin » Wed Apr 13, 2022 6:02 am

Through some quick searching and a few scans-

from:
https://ls1tech.com/forums/conversions- ... vpw-6.html

The volt message works like this-

19 volts = 0xE8,0x73,0x40,0x08,0x07,0x8C
9 volts = 0xE8,0x73,0x40,0x08,0x03,0x84
14 volts = 0xE8,0x73,0x40,0x08,0x05,0x88

E8 - Priority 7, 3 byte, No In-frame response allowed, Function address, Function Command/Status
73 - Status ID for Table - 24 Charging system messages of SAE J2178-4
40 - sent from BCM (if 40 is used, the status will reset to bottom of scale in a few seconds if message is not reset. can be sent from 10 - PCM
08 - Sec ID from table (not in SAE J2178-4)

078C- hex for 1932 (it appears the value is sent in hundredths of volts, converted to hex)

The messages are similar format to oil pressure (Status ID 4B, Sec ID 11) , coolant temp (Status ID 49, Sec ID 10).


Through some brute force I know the data to be modified is in this range- left does not work. right does work. so getting close.
Capture.JPG

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Re: Switches for turning on/off J1850 VPW information

Postby RADustin » Wed Apr 13, 2022 1:05 pm

I think I found a single bit that makes it work or not. currently testing it. :punk:

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Re: Switches for turning on/off J1850 VPW information

Postby RADustin » Mon Jul 18, 2022 11:56 pm

revisiting this. I have the volt gauge working but I think it's only updating at key on and not while the engine is running. I need to play with it some more.

But basically I know there are class 2 data message switch tables located in the system segment. I'm not smart enough at this time to get this part of the code to disassemble in ghidra so I'm curious what info may be available for these tables? I know it's possible to control the underline on the PRNDL indicator on gauge cluster and to control the security light because those turn off when I use a kodiak system segment (and the volt gauge full functionality turns on).

I'm not sure how tables are references and called in assembly and maybe learning that could lead me to some clues? not exactly sure my game plan here- trying to avoid brute forcing the solution; a roadrunner would be nice though.

thoughts? TIA

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Re: Switches for turning on/off J1850 VPW information

Postby Highlander » Sun Sep 11, 2022 6:58 am

This means you need to enable the different phases.. what OS are you running?

There is a total of 12 phases if I am not mistaken
PwrUpPh1Enable UnlockPh1Queue UnlockPh1Enable UnlockPh2Enable RunPh1Queue RunPh1Enable RunPh2Enable RunPh3Queue RunPh4Enable CrankPh1Queue CrankPh1Enable CrankPh2Enable

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Re: Switches for turning on/off J1850 VPW information

Postby RADustin » Mon Sep 12, 2022 11:05 pm

Highlander wrote:This means you need to enable the different phases.. what OS are you running?

There is a total of 12 phases if I am not mistaken
PwrUpPh1Enable UnlockPh1Queue UnlockPh1Enable UnlockPh2Enable RunPh1Queue RunPh1Enable RunPh2Enable RunPh3Queue RunPh4Enable CrankPh1Queue CrankPh1Enable CrankPh2Enable

yep from what I can tell you are correct but I still don't have the bit mapping.

using the ...603 or ...618 OS.

I have it working but I'm hesitant to post what I did because it's just a random un-educated guess/hack. I do want the bit mapping though- seems like this is the same structure in all 1mb and 512k PCMs.

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Re: Switches for turning on/off J1850 VPW information

Postby Highlander » Thu Nov 17, 2022 4:41 am

Did you define the table that enables the bit mappings?

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Re: Switches for turning on/off J1850 VPW information

Postby ShorTuning » Mon Nov 21, 2022 11:55 am

I'd be interested in more info into this matrix. I am trying to make traction control communication work in a Fbody using a P59.

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