CVN's Explained.

[GMPX]

Hi All,

Something we are asked about quite often is to do with CVN's. What are they? What do they do? So I thought I would do a quick explanation. Scattered throughout this forum is various discussions on it, so it was time to summarise in to one thread.

Q - What is a CVN?
A - CVN stands for "Calibration Verification Number", this is a fancy name for checksum (http://en.wikipedia.org/wiki/Checksum). What the ECM (or TCM) does is add up all the numbers within each segment of the flash memory, the total of those numbers is what the CVN equals. This allows people with a TechII to quicky check the data in each segment is correct or unaltered (eg, the CVN matches a known program).
If any data is altered within the segment then the checksum (CVN) will change or not match what it originally was.

The CVN can also be used by tuners to uniquely identify their own calibrations without needing to read out the ECM / TCM.
EFILive allows workshops (or stream owners) to modify the CVN to whatever value they desire.
As an example, a stock E38 CVN list might be as follows -

Segment Name Part Number CVN
Operating System 12612381 50D6
Engine Operation 92200744 26BA
Engine Diagnostics 92200743 0B9F
Fuel System 92196978 D0EB
System 92200742 16E2
Speedometer 92196106 C405A tuner might wish to change each CVN to a pattern they can quickly recognise -
Segment Name Part Number CVN
Operating System 12612381 AAAA
Engine Operation 92200744 BBBB
Engine Diagnostics 92200743 CCCC
Fuel System 92196978 DDDD
System 92200742 EEEE
Speedometer 92196106 FFFFOR
Segment Name Part Number CVN
Operating System 12612381 50D6
Engine Operation 92200744 1001
Engine Diagnostics 92200743 1000
Fuel System 92196978 2004
System 92200742 1000
Speedometer 92196106 3000In the last example the CVN of the calibration segments could be used to indicate a version of the tune, so Engine Operation v1.001, Fuel System v2.004.

CVN editing is only available to customers who have the stream enabled for the controller they are trying to correct the CVN on. Anytime the CVN is altered from the stock value the vehicle would no longer meet EPA / CARB emissions regulations. Please keep that in mind if you are thinking of putting in some custom patterns like those above.
You must be very careful not to alter the CVN's to a value already used by the manufacturer, please see page 99 of the SAE HS-3000 purple book for more on this.

How to alter the CVN in EFILive -
Click on the CVN Tab (with a E38,E40,E67,T42 or T43 file loaded and active stream for that controller).
Click on the CVN value you wish to alter and enter in the new number (using only letters A - F and numbers 0 - 9). Hit enter.
Then click the 'Update' button and save / reflash the file.

Many early controllers did not support CVN reporting, it really came to light after about 2006, CVN customisation for the Bosch Diesel ECM is not possible.

Cheers,
Ross

[Nemo]

Well put, made it easy for the n00bs like me. :)

-Nemo

[GMPX]

Just trying to reduce Emails for support :)

[Nemo]

:hihi: Haha, yea, sorry about that...

-Nemo

[Chuck CoW]

So, I'm assuming the CVNs that Live displays are the the original "correct" CVN for the original calibrations and do not change as live alters the cals. I would imagine that unless you continue to read the cal multiple times from the pcm, the CVN should always report the original correct CVN??? SO, we can use this for a reference when wanting to put the original CVNs back???

What would be cool would be the ability to load (after the modified tune is finished) the original cal/bin file as the "alt" calibration and be able to toggle between the 2 CVN fields so as to permit a copy/paste operation making it easier to put the "correct" CVN's back into the pcm....

My suggestion would be to show the CVNs where Live currently displays them, but also build the CVN parameters into the flowchart/tree on the left of the editor in a RED folder like the throttle response tables so as to permit easy comparison/modification of the CVN.

I'm assuming you'll need to "full flash" the controller to restore the correct CVN?


Chuck CoW

[GMPX]

See answer here -
http://forum.efilive.com/showpost.php?p=82566&postcount=9

[rcr1978]

"please see page 99 of the SAE HS-3000 purple book for more on this."

Where can I find this?

[GMPX]

"please see page 99 of the SAE HS-3000 purple book for more on this."

Where can I find this?
It's a little pricey!
http://www.sae.org/technical/books/HS-3000/2006

For copyright reasons I probably can't quote the text, but it's along the lines of if someone other than the manufacturer changes the flash data then a new CVN must be created. Which is exactly what you would be doing by entering in your own CVN.

Cheers,
Ross

[rcr1978]

So basicaly if the flash data was changed and the CVN was not or was made the same again a emission law would be violated.

[GMPX]

So basicaly if the flash data was changed and the CVN was not or was made the same again a emission law would be violated.
Correct, if you change something in the tune and then correct the CVN to the factory value that is an emissions violation, of course we could have easily made the software do that but that CVN correction function is not about that.
I use the analogy that if you buy a gun you choose to shoot at a target, wildlife etc, or you choose to commit a crime with it. Same for this, manual CVN correction has a perfectly legitimate reason to exist, if you choose to use it illegally that is your choice.

Cheers,
Ross

[joecar]

For non-stream usage, can the CVN tab be made to display the CVN's...?

[ScarabEpic22]

joecar, it is there on the E38 sample tune in the latest download. I dont have any idea about other PCM/ECM/TCMs but I have the same verbage as you show there for my P10.

[GMPX]

It's only going to show on late model ECM's/TCM's, LS1 has no CVN in place.

Cheers,
Ross

[LetsGoBrandon]

Does EFI Live disable any of the monitors, say for a '06 5.9 Cummins?

Thanks,

4c6574277320476f204272616e646f6e21

[GMPX]

No, emissions manipulation isn't possible.