Originally Posted by grantv

Measuring the VATS (Vehicle Anti Theft System, that's all); this is only the resistance of the key. Inside of the key is a resistor to make it a bit more difficult for would-be thieves/amateurs to copy a key. Your ignition will only read one that is for example 2.37K ohms. This has nothing to do with the key profile or actually starting your car however. The right resistance only allows the ignition to read that this key (with no teeth cut at all for that matter) is allowed to engage the car. There are 15 different VATS measurements, so you have a 1 in 15 chance that my key will be "allowed" in your car.

As for an original being more accurate, you can also say a photocopy of a drawing from a machine shop that had greasy fingerprints on it making some areas hard to read might be fine, and then another copy of that... eventually you're done. Print a new copy.

Inside your tumbler is a matching set of teeth for your proper key. If your key is worn out you won't properly engage the tumbler. Imagine to exaggerate, you only have tiny little corners left that meets up with the tumbler inside. In short time you will wear out both the key and cylinder/tumbler. Now you have a bigger problem. A perfect matching key/tumbler will align everything inside and prevent internal wear.

Either the car starts or it doesn't, yes. For now. But remember that your worn out key is wearing out your tumbler faster. And eventually you just might not start, maybe time to have your tumbler re-keyed. OK, maybe I paid too much, but $100 is pretty cheap insurance IMO. This is Canada.

All just IMO. I am not a locksmith, just did some research for fun previously.

Originally Posted by grantv

No! 😔 Sorry, me again...
If all keys with same VATS (ohm reading) had the same profile we'd have lots of thefts. They can call up the original key profile using the VIN at either a dealer or qualified locksmith. No need to look at the tumbler. For that matter the car doesn't need to be there short of proof that it's yours, and testing the key after.
All this is assuming nobody ever changed the tumbler (not too common, usually caused by either a worn out key or very heavy keychain).

Originally Posted by grantv

No! 😔 Sorry, me again...
If all keys with same VATS (ohm reading) had the same profile we'd have lots of thefts. They can call up the original key profile using the VIN at either a dealer or qualified locksmith. No need to look at the tumbler. For that matter the car doesn't need to be there short of proof that it's yours, and testing the key after.
All this is assuming nobody ever changed the tumbler (not too common, usually caused by either a worn out key or very heavy keychain).

Originally Posted by laurent_zo6

It makes sense that a same profile would not be good. So what does a profile look like when a dealer or qualified locksmith calls for one? And does each VIN has a separate profile?

Originally Posted by grantv

Sorry for the delay, but here's my locksmith VIN made key at left, and the one key that came with the car to the right. If you made a copy of the right key... it would look like the right key. Premature wear to the tumbler will likely occur, eventually ending in a much more expensive fix than a properly made key.
The right side key is in my house as a backup only, not used.
I'd assume each VIN has it's own profile.

Originally Posted by thisMSGgood4me

Man, that right key is really worn out. I wouldn't even try using it anymore. Just get a second new key made as a backup (with that new one on the left as a guide), throw that old worn out key away and then you'll be all set.

Originally Posted by laurent_zo6

And does each VIN has a separate profile?

Originally Posted by Lee DeRaud

Not even close. To get the keys to work with normal manufacturing tolerances, there are a relatively low number of possible tumbler pin heights (almost certainly less than 10, probably more like 6-8) and a relatively low number of tumblers (again, somewhere around 10 max)...best case that totals out to 100 different profiles. Multiply by the number of VATS resistance values (15), and there are only about 1500 possible keys.
(I suspect the actual number is about half that.)

Originally Posted by laurent_zo6

So basically I have one chance in 1500 that a neighbor who drives a C5 has the same key as me?

Originally Posted by laurent_zo6

What is the exact information that the dealer has to make a key based on your VIN if you come in without a key ? Is the info on a card? does it show tumbler pin heights or just a code that the dealer input into a machine and the machine makes the key based on the vats number?

Originally Posted by Lee DeRaud

Pretty much. That's decent odds, IMHO, if you think about how long it would take if you had a full assortment of keys to try.The question of how a dealer gets the info from the VIN is above my pay grade...probably has to call somebody or access a computer back at GM headquarters. But it boils down to cutting the right peaks and valleys onto a blank with the right chip resistance: a list of ten or so numbers, one of which is the chip value.

Originally Posted by laurent_zo6

Thanks. I have 2 keys and not letting them out of my sight. . For good measure I am going to make a duplicate key without resistors just in case I lock myself out.