GM 0411 ECM VATS Bypass Class 2 Serial

American GM ECUs and PCMs
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GM 0411 ECM VATS Bypass Class 2 Serial

Postby scoutcamper » Thu Oct 25, 2018 10:17 am

Hey All,

Just took my K5 to the CA Smog Referee today, from a mechanical point of view I passed easily, from a software point of view I failed and I need some help.

They are telling me I have to take the truck to the dealer and have them flash the PCM with stock code, not a big deal, EXCEPT, that means I have to retain VATS somehow. Since the donor vehicle was a 2001 Tahoe that means VATS was controlled by the BCM, which I don't have on my swap. I have not found any bypass modules that simulate the class 2 serial of the BCM to allow VATS to work.

The referee said that they will read out the PCM and compare the calibration to a known stock one provided to CA SMOG by GM, and if it doesnt match then you automatically fail(not sure I buy that or not....)

My concern with bringing over a BCM, aside from all the other check engine codes that it might introduce, is that I cant find a good wiring diagram, plus then I am still stuck needing to do some kind of bypass because I am not changing out my key in my column for a VATS key(no room)

I am super close to passing smog, I passed the visual, the dyno, the tailpipe sniffer, this is my last barrier to a smog legal swap, I am hoping someone can help me out!

Has anyone ever built a VATS/BCM emulator that can work for this situation?

Thanks,
Scoutcamper

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Re: GM 0411 ECM VATS Bypass Class 2 Serial

Postby pman92 » Thu Oct 25, 2018 8:03 pm

I don't have the answer but am very interested in knowing how the class 2 VATS works and what a BCM simulator would require

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Re: GM 0411 ECM VATS Bypass Class 2 Serial

Postby roughneck427 » Fri Oct 26, 2018 1:35 am

I’m in CA also and never had to do that. I have programmed several vehicles that now have a sticker. Are you using a calibration that is for the VIN in ecm? Verify it against GM TIS. Unless they are looking at the CVN when the poll the ecm and verifying it against the TIS data.

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Re: GM 0411 ECM VATS Bypass Class 2 Serial

Postby j_ds_au » Thu Nov 01, 2018 6:55 pm

Is the VATS flag within the Cal portion of the Bin? If so, you're in a bind, if not, you just need to flash the Cal portion of the Bin with stock, not the whole Bin. HTH.

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Re: GM 0411 ECM VATS Bypass Class 2 Serial

Postby antus » Sat Nov 03, 2018 2:24 pm

Yes it is a flag in the cal portion. Im not sure about this cvn check, as far as I could tell when I looked in to it, if you set the flag and update the checksum the cvn doesnt change unless the software you are using updates it for you. You can verify its not right by downloading the whole bin and re-calc the cvn and see it doesnt match, but then if you are going to download the whole thing and calc the cvn why bother putting it in the calibration? Since the sum is just a sum, if you wanted to you could add some junk data in an unused space to keep the original checksum too. Just remember checksum is a 16bit calculation, so see how far out your checksum is and write a 16 bit value of the difference between the original sum and what you want it to be. Larger if you need to overflow past FFFF and come back to a lower sum. But having said that, the OEMs dont seem to use it to verify changes from stock. The whole system seems a bit pointless to check for mods.
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: GM 0411 ECM VATS Bypass Class 2 Serial

Postby roughneck427 » Sun Nov 04, 2018 7:20 am

antus wrote:Yes it is a flag in the cal portion. Im not sure about this cvn check, as far as I could tell when I looked in to it, if you set the flag and update the checksum the cvn doesnt change unless the software you are using updates it for you. You can verify its not right by downloading the whole bin and re-calc the cvn and see it doesnt match, but then if you are going to download the whole thing and calc the cvn why bother putting it in the calibration? Since the sum is just a sum, if you wanted to you could add some junk data in an unused space to keep the original checksum too. Just remember checksum is a 16bit calculation, so see how far out your checksum is and write a 16 bit value of the difference between the original sum and what you want it to be. Larger if you need to overflow past FFFF and come back to a lower sum. But having said that, the OEMs dont seem to use it to verify changes from stock. The whole system seems a bit pointless to check for mods.



Being in California the state it heading towards the Euro style program checking CVNs So do to a swap with drivetrain not original to the swap you have to go to a “referee” they validate it has the emissions equipment from the donor vehicle and the correct unmodified calibration in the ecm. It could be the vin the poster provided from the donor doesn’t have the same or latest calibration verified against TIS hence get it updated

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Re: GM 0411 ECM VATS Bypass Class 2 Serial

Postby j_ds_au » Mon Nov 05, 2018 2:38 am

antus wrote:Yes it is a flag in the cal portion. Im not sure about this cvn check, as far as I could tell when I looked in to it, if you set the flag and update the checksum the cvn doesnt change unless the software you are using updates it for you. You can verify its not right by downloading the whole bin and re-calc the cvn and see it doesnt match, but then if you are going to download the whole thing and calc the cvn why bother putting it in the calibration? Since the sum is just a sum, if you wanted to you could add some junk data in an unused space to keep the original checksum too. Just remember checksum is a 16bit calculation, so see how far out your checksum is and write a 16 bit value of the difference between the original sum and what you want it to be. Larger if you need to overflow past FFFF and come back to a lower sum. But having said that, the OEMs dont seem to use it to verify changes from stock. The whole system seems a bit pointless to check for mods.

Interesting. Would the ECU itself not generate some DTC if the CVN doesn't match the Cal? Assuming the CA referee isn't checking the Cal in its entirety (as in byte per byte), then I'd expect they'd be checking the CVN is correct per factory and that the Cal actually matches the CVN (by DTC if applicable, or checking against the Cal itself). So the original CVN would be required, and as you say, a spare byte or two adjusted so that the Cal matches this.

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Re: GM 0411 ECM VATS Bypass Class 2 Serial

Postby antus » Tue Nov 06, 2018 11:36 am

Not in the 0411 generations. I left it the CVN and updated the Checksum just to see if I had missed something and everything was fine. Its a CRC16, where as the sum is exactly a sum, so its more computationaly heavy to calculate. I expect it was a case of "get it out there" as a concept and build it up further in the later generations.
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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