Re: remote entry -key fob programming

maxpower wrote:

> The RKE system and transmitter use a rolling code method  ... 
> The transmitter sends a randomly selected sequence code each time
> The code increments vary depending on a unique algorithm that
> is preprogrammed to each transmitter at the time it was built. 
> The sequence changes each time the transmitter is used. 

> the sequence code cannot be calculated from the encoded
> transmission. The receiver module also learns the transmitter
> id code

So far, what you're saying is that the FOB sends out a different
sequence each time it's pressed, and that the ID code of the fob can
be uniquely calculated from the transmitted data stream based on an
algorythm.  

I doubt that the fob actually does generate a completely different
stream each and every time it's pressed, as I doubt that the designers
would ever anticipate someone with enough electronic gear would be
close enough to the car to (a) want to open/unlock the car without
possessing the real fob or key, (b) be close enough to evesdrop and
capture the transmission, and (c) possess the electronics required to
replicate the transmission.  Just consider a use-case situation.

But even if the fob does generate a different stream each time it's
pressed, then I guess the receiver in the car would have to never
respond to the same stream twice.

> and initial sequence code at the time of transmitter programming.
> The receiver then expects the next transmitted sequence code to
> increment within a predetermined range of numbers

Now that has got to be total bull****.

I can see plenty of situations where the fob and receiver can get out
of sync with each other.  There would be no need for this
syncronization if the fob simply generates different streams that
algorythmically always reduces to the same unique ID code.

> Transmitters and receivers are unique to each vehicle line and
> will not work.

I guess we'll have to wait and see if John Keith posts back his
results.

> 1999 Plymouth Voyager and 2000 Dodge Caravan

And by the way, do those 2 vehicles have sentry-key?

If so, would they/could they have the same physical ignition key?