Two Prii - one smartkey?

Sorry to be the bearer of disappointing news, but it would be extremely difficult to do. I'd like to do it too. The problem is that the fob and car are associated and change their code in a pseudo-random manner with each start. It would be very difficult to get the two cars in sync with their codes and keep the fob in sync too.

Different key chains/fob ornaments attached to each fob...

 

<div class='quotetop'>QUOTE(Bill Merchant @ Mar 12 2007, 11:29 PM) [snapback]404557[/snapback]</div>

Theoretically it should work. The fob/car pair allows for up to 250 or so steps away from the last pairing. This is to prevent getting out of sync if you press the fob button(s) while out of range from the vehicle.
But if you kept the crossed fobs/cars separate for over 250 or so iterations, then the crossed fob would lose sync eventually.

To clarify, lets say you have fob A for car A and fob B for car B with no other fobs. You could program fob A to work with a second memory slot in car B and vice-versa.
Now if fob A is away from car B and is used for car A for say 10 presses of the fob (or SKS function). Car A is still ready for the next code sequence, but car B will be out of sync. Well, not really. Car B will look ahead for up to the next 250 sequences. We are still within this range, so fob A will still work for car B.
But lets say you take a trip with car A for an extended period of time. The fob A dishes out 500 codes to operate with car A. Now when fob A is attempted to operate car B, its sequence is too far out for car B to accept. It will have to be re-syncronized.
Some have said that the fob and car can resync by putting the fob in the slot. This type of RFID is a different system than the long range rolling code so the fob could be authenticated, and then the car could accept a resync. I don't know if this is true or not though.

 

<div class='quotetop'>QUOTE(DanMan32 @ Mar 14 2007, 01:20 AM) [snapback]405248[/snapback]</div>

So are you saying that if I use only one fob and keep the other stashed away and never get it near my car it will become useless? I live alone and am the only driver of my Prius so I end up carrying one fob and keeping the other in a drawer in my desk. Must I make an effort to alternate using the two fobs in order to keep them synched with the car?

Tom Wright

 

<div class='quotetop'>QUOTE(RedRockPrius @ Mar 14 2007, 11:34 AM) [snapback]405409[/snapback]</div>

No, the codes are maintained separately for each fob. If you used a given fob extensively with another car, or just went a distance away and pushed the fob buttons several hundred times, then you would need to resync. Just sitting in a drawer is fine.

Tom

 

<div class='quotetop'>QUOTE(qbee42 @ Mar 14 2007, 08:49 AM) [snapback]405425[/snapback]</div>

But he is saying that for the guy with two 2007 Prius, only two of the four FOBs would be usable - the other two would no longer be functional.

That's because each car has only 2 memory slots: A and B. The A slot would be synced with FOB 1 for car 1 and the B slot would be synced with FOB 2. Meanwhile, in the other car, A slot would be synced to FOB 2 and the B slot with FOB 1....

 

Has anyone seen any official document that shows the Prius to synchronize the fob with the car with rolling codes? I thought it was mostly speculation that such rolling codes existed, but I have never seen any evidence. I suppose one way of proving it would be to activate two cars on one fob and then use a single car 251 times and see if that disables access to the other car.

 

theoretically it may be possible but good luck finding someone who can pull it off in practice. :blink:

 

This sounds like a perfectly reasonable question, but the answer's not so easy. Assuming the fob and/or the car could be reprogrammed for different cars, this would circumvent the security Toyota has obviously gone to a great deal of trouble to build in, and make it too easy for anyone with a fob to drive any Prius they wanted. I wouldn't doubt that a portable code-stealer is in the works somewhere, but we're not there yet.

Sorry, let me paraphrase: 'No, 'because then somebody could steal it.'