Prius smartkey question

It's a used key. Only the immobilizer will work. The other parts can't be set back to synchronize with the car, as the ECU expects a new key fob.

Tom

 

Actually, it's the car that is programmed to recognize the keyfob. The black logo keyfob has a counter in it that increments by one each time a key is pressed. Apparently it is only possible to program the car to add a keyfob that has been used some small number of times. The silver logo keyfob uses a different encryption chip, but it behaves in much the same way.

If you're really interested, go the Microchip website and download the data sheet for a HCS362 encryption chip. It is used in the black logo keyfob. Note particularly the section on "limited seed" mode. It limits transmission of the seed value to a counter value of 127 or less. I don't know if Toyota uses this mode, but it would account for the observed behavior.

 

Exactly. As posted above, the car is programmed to accept the fob, not the other way around. For security reasons, you cannot add a fob that has been used for more than a small number of cycles.

Microchip makes the guts for these things. Their web site is a good source of technical information if you want gory details.

Tom

 

http://priuschat.com/forums/care-ma...21501-end-don-t-lose-your-keys-else-myth.html

Check this link out.

 

Different issue. The link is for a thread about programming the ECU to use new fobs without having an existing fob. The OP of this thread wants to use and OLD fob and still has a working fob.

Tom