CA/LA Smog

[terra]

terra do you know if the CVN is a calculated value or stored value?

It's calculated. Exactly how it's calculated isn't entirely clear to me. IIRC @gpetersen found that if you brute force the checksum such that the calculated checksum is equal to the stock value, then the CVN is also correct. So it's either itself a CRC16 (of each half) with a different initial value and/or polynomial, or it's some sort of calculation that's done to the calculated checksum.

Probably wouldn't be crazy difficult to hardcode the program to return a valid value

[T-Rex]

This new insanity is all the motivation I needed to finally start an LLC in another state...

CA really loves making our lives as miserable as possible

[oceansize]

IDK how the CVN check would do anything without the manufacturer data to check against

Supposedly they have a database. Quote from the one PDF below. It is all over the map though in terms of what years it starts. On the EVO forums they said 2006. On that CA BAR website I found 2000. Another PDF says 2008.

"Section (g)(4.7.4) of the OBD II regulation requires manufacturers to submit CAL ID and CVN information. A template titled “CAL ID and CVN Data” is provided in this Mail-Out as Attachment E. For 2008 and subsequent model years, manufacturers are required to use the Microsoft Excel electronic template provided on the ARB website http://www.arb.ca.gov/msprog/obdprog/obdprog.htm for reporting and electronically submitting CAL ID and CVN data to ARB. For the electronic submittal, manufacturers may email the data to ARB staff"

EVO forum thread discussing people actually hitting this issue:

https://www.evolutionm.net/forums/ge...se-help-2.html

Data collection forms for CAL ID and CVN for manufacturers:

https://ww2.arb.ca.gov/resources/doc.../obd-resources

[skristedja]

This would be the best possible outcome for all my e46 m3 holmies in CA. This little blurb says model year 2000 and later. https://www.bar.ca.gov/ARSC/Newslett..._Modifications

beginning July 2020, BAR will implement Cal ID and CVN checks for most model-year 2000 and newer vehicles as part of the On-Board Diagnostic Smog Check inspection failure criteria

IDK how the CVN check would do anything without the manufacturer data to check against

[heinzboehmer]

The checksum value is stored in the DME memory. The DME then recalculates this checksum based on what's in the rest of memory and if the two values don't match then the car won't work.

So potentially, if the smog computers are just reading the checksum value out of memory, you might be able to fool them by storing a "stock" checksum. Would require some program changes to disable the checksum check on the DME itself though, as the stored and calculated values would differ.

[oceansize]

The e46 may be exempt. Manufacturers were not required to submit CAL ID and CVN info for 2007 and prior years.

Page 6 of http://ww2.arb.ca.gov/sites/default/...og/msc0623.pdf

This would be the best possible outcome for all my e46 m3 holmies in CA. This little blurb says model year 2000 and later. https://www.bar.ca.gov/ARSC/Newslett..._Modifications

[oceansize]

heinzboehmer has it correct.

Everyone needs to realize that if the CVN is indeed a checksum, which is how it reads, rather than a simple stored value then any modification to the DME will cause you to be flagged as your CVN would then be incorrect. I can't believe CVN is a simple stored value because it's usefulness as a software modification check would then be zero. It almost assuredly is a calculated value. If you aren't a computer guy your thinking what do you mean calculated? A little formula using the OE software engine parameters as inputs will be used to produce a value. Change an engine parameter, change the value that is produced by the calculation.

terra do you know if the CVN is a calculated value or stored value?

[skristedja]

The e46 may be exempt. Manufacturers were not required to submit CAL ID and CVN info for 2007 and prior years.

Page 6 of http://ww2.arb.ca.gov/sites/default/...og/msc0623.pdf

CAL ID & CVN
Section (g)(4.7.4) of the OBD II regulation requires manufacturers to submit CAL ID and CVN information. A template titled “CAL ID and CVN Data” is provided in this Mail-Out as Attachment E. For 2008 and subsequent model years, manufacturers are required to use the Microsoft Excel electronic template provided on the ARB website http://www.arb.ca.gov/msprog/obdprog/obdprog.htm for reporting and electronically submitting CAL ID and CVN data to ARB.

[EthanolTurbo]

[heinzboehmer]

Sure, if the CVN and CAL ID are just constants stored in the firmware (serial numbers, hardware/software numbers, etc), then getting past these checks is trivial.

However, the documents posted make it seem like the CVN is actually a checksum. This is a mathematical operation that is performed on the entirety of the software to produce a number. So yes, even if you change a single bit, the checksum will change too.

[Tbonem3]

You get like 30 flashes, but each one uses two slots iirc, so more like 15.

I really don't see how modifying a little code is going to change the serial numbers. As long as the ECU is your original, should be fine I would guess.

[heinzboehmer]

What's your source on this? I'm going through the regs right now and haven't seen this, only saw it was proposed

Page 9 of the link Samsonite79 posted: https://www.bar.ca.gov/pdf/BAG/20210...d_Software.pdf

[jet_dogg]

Finna cop spare dme.

[Epsilon]

Don't you get a finite number of flashes before you have to virginize your DME? Each SMOG is like 1 flash to return to stock and another to go back to CSL.

[skristedja]

Oh shit this software thing goes into effect Jul 19. I'll do what I can to get my car smogged this week. That will at least buy me two years before I have to get it smogged again.

What's your source on this? I'm going through the regs right now and haven't seen this, only saw it was proposed