Smart Key?

1. It's not possible to program the Prius to recognize a Smart fob unless you have access to the Toyota diagnostic laptop or hand held device.

2. Used Smart fobs purchased on eBay may not be recognizable by your Prius because the fob contains a counter that increments each time the fob is used. The Prius will refuse to recognize a "new" fob whose counter has increased above some small number.

 

Get the replacement from a dealer and be done with it, before you lose the other one. It gets *way* more expensive if they're both missing.

Key strategies: put all keys on the fob and *always* lock your house doors using the key. (We installed deadbolt locks specifically to enforce this.) This forces you to have the house key, and thus all keys, in hand. Always put the keys in the same place.

 

I have SKS and my solution for a cheap spare/extra key is to buy the cheapest silver or black fob from ebay I could find and program it to work in the dash to start the car. Instructions are on this site to do this. Either type fob can be programmed to work in the dash to allow the car to start. Then get a key made for the drivers door lock and grind the keychain end to fit the fob. Just use the old key you get with the ebay fob as a template for the keychain end. The key matches a standard Toyota blank and can be duplicated anywhere.

I keep my other fob at home in a safe place and carry the ebay fob as a spare. If I lose the fob that came with the car I can use the key and ebay fob to get home. One thing you don't want to do is lose both fobs that came with the car as that costs $$$ to reprogram the car and to buy new SKS programmed fobs.

If I had a driver that was prone to lose keys I'd give them the cheaper fob and let them do without the SKS. Then if the fob is lost you're only out <$50 instead of $$$'s.

 

Also, I read here in the forums that you can only program a Prius to accept a maximum of 5 SmartKeys. So even if you don't mind paying to get the fobs replaced, you could get to the point that you could no longer program the car to recognize a new SmartKey.

The great thing about the SmartKey system is this: it never has to leave your pocket or your pocketbook. Just put it in there, and never take it out. As long as the SK is on or near your person, you can unlock, drive, and lock the car without the SK ever leaving your pocket or purse. Very cool. So it should be harder to lose a SK than a regular car keyfob.

 

I purchased a used smart key (silver logo) on ebay...per other post on prius chat,,I instructed toyota tech to just program portion of smart key to act as "ignition key" of to deactivate immobilizer...they were able to perform this for me for $45.00.... I now have a hidden, inside car spare smart (albeit..not really that smart) key to put in ignition slot to start car..and a hidden, outside car, mechanical key to get into car...I'm set for all eventualities...locking smart key in car...loosing smart key(s) ..etc

 

I believe the number is four Smart Keys, and that relates to the number that can be used at any one time. You can always remove an old Smart Key and add a new one, so there is no worry about filling up the slots.

Tom

 

Strap that key to your cell phone. I bet you'll never lose it then!

 

Patrick,

I can't imagine this being a problem; the keyfob is probably not storing the counter value as a double long int so I'm sure after just a few key presses you can roll that counter back over to zero to reprogram the keyfob to the car...

~ dan ~

 

Someone remind me there's a free Prius waiting for me in Trinidad, please.

 

No, it isn't that simple. Once a fob is no longer new, which means a small number of presses, it can no longer be associated with a controller. It is designed this way on purpose. Furthermore, you don't reprogram the keyfob to the car. The car is programmed to accept the fob.

Tom

 

I apologize for using poor syntax; I understand the car does all the 'thinking' but I find it stupid that a fob can no longer be associated with a controller. So, from what you're saying I infer it's not a keypress counter we're talking about but a flag that, once set, prevents it from re-associating with a car.

I find it hard to believe that it can't be flashed somehow. Actually I don't believe it's possible to make it impossible to reset, design consideration or not. It's always possible to replace an SMD component if absolutely necessary. But is the flag REALLY stored on one bit of NVRAM? If I pull the battery out for several days that won't be enough to unset the flag? Do I really have to replace a component?

~ dan ~

 

The fob uses a Microchip Keeloq. All of the keystroke counting is done on the chip, not on some separate piece of memory. Using external memory would be a huge security risk. If you want to change the data in the Keeloq, you will need to use micro-machining techniques and direct probing of the die. Even then I wouldn't expect it to work, since the package is designed to self destruct when subjected to that sort of attack.

Tom

 

The black logo keyfob uses a Microchip HCS362 Code Hopping Encoder. The datasheet for it is available at the Microchip website. The usage counter is 16 bits. There is a mode described in which the seed value (necessary for pairing with a receiver) is only transmitted when the usage counter is in the range of 0 to 127. This mode could be the limitation on usage of used black keyfobs. The procedure for flashing it is fully documented, and you could probably do it without even removing the chip from the circuit board.

The only problem with reflashing it is what data to put into it. There is a 60-bit seed value which is transformed by the receiver into an encryption key. So you have to know how to design an encryption key, and then how to encode that key as a seed value. These are Toyota/Microchip secrets.

Some cryptology experts have succeeded in breaking the Keeloq system used on devices such as garage door openers. The black logo keyfob uses essentially the same system, so they could probably do the same to it. A key component of their crack was that they used a lab instrument that recorded the power fluctuations of the receiver as it decrypted a transmission. So the message is that a half dozen professional cryptologists using expensive lab gear have cracked a system similar to the black logo keyfob. They didn't crack the Toyota system, only a similar one that they had full documentation of the receiver.

The silver logo (SKS) keyfob uses a different chip that is not publicly documented. The transmission protocol is even different (Manchester encoding for the silver logo, pulse width encoding for the black logo).

 

It's probably how I would have expected it to work because it's more secure and cheaper, but it's still evil.