Yeah, maybe this scheme is to "deactivate" a lost key. Unless the lost key has a tag which can identify its vehicle, if you found this key, you'd need to walk past potential vehicles and press the open button to see if that's indeed the vehicle. This scheme would (eventually) prevent that. If you found the key, you could of course always try that on the doors of potential vehicles, but that would look very suspicious.The1 wrote:i would think it would be so if you lost your key then it would stop someone eventually finding it and being able to open your car, though it will work and update itself once used in the ignition, so BCM must have some kind of timer or last X number of rolling codes only stored, key may still retain a master value that works in the barrel so it can disarm to get a new rolling code, perhaps that's what these people have worked out via the BCM serial number.
I don't think that the rolling key code is checked when the key is inserted into the reader, as that wouldn't serve any practical purpose (a bad rolling key code has no effect here). Only the respective ID(s) would need to be checked, most likely via an encryted data exchange via the reader (although I do wonder if the key reader interface is actually bi-directional, or if it's uni-directional, from the BCM to the key fob, with the key fob's RF transmitter being used for the other data direction).
Joe.