2 Prius Keyed the Same?

Even if they could, I would personally consider that a bad idea. It could be a liability at some point in the future if you sell the car.

 

The fobs use a rolling code which updates with each use. Using one fob on two cars will cause the fob to lose synchronization. There have been several attempts to make this work, but I haven't heard of any success with it.

Tom

 

I would guess (based on what I learned about SKS) that it would work only if the SKS-ECU is at least four-channeled. I am sure the SKS is at least dual-channeled since we have TWO separate keys. (e.g. use your key #1 for 2 years. The key #2 still works). Each key can search forward 256 codes to match the new codes given by SKS-ECU. The ECU was made (during pairing) to recognize the key so that it knows the code sequences to perform code rolling. The ECU is programmed to recognize keys (not the other way around). Therefore, technically, you can have both ECUs recognize the same set of keys. However, if the SKS-ECU can only recognize two at most, them it becomes overriding when the third or fourth join the party.

Since over-engineering costs $$$$ for Toyota, I am not betting on that the ECU can support more than two channels. That is just my educated guess, anyway.

Do keep us posted of the outcome. Thanks in advance.

 

The ECU is four channeled. The fobs, however, are single channeled. The problem isn't with the ECU, since it can keep track of all four fobs. The problem is that a fob gets bumped along by the ECU on car A, and then confuses the ECU on car B at a later date.

Tom

 

Further, the Toyota service policy on this is to program the vehicle only to recognize a new fob, not previously used ones.

 

It's more than policy. I think that a keyfob only transmits the data necessary for programming for the first 128 times a key is pressed. This would explain the mixed, but generally bad, experience with programming used keyfobs.

I took apart a black logo keyfob (non SKS). There is a Microchip HCS362 "KeeLoq Code Hopping Encoder" in it. The data sheet discusses a mode called "Limited Seed". In section 3.3.1, example B is the following statement:

This sure sounds like the behavior that we see with attempts to program used keys.

I also took apart a silver logo keyfob (with SKS), and it uses a different chip with numbers on it that I couldn't track down. So it may be entirely different, but I doubt it. It probably uses a similar protocol, except that the SKS fob can respond to queries from the car.

The synchronization counter is 16 bits, which means that it will wrap to zero every 65536 usages. So there may be a way to reset a keyfob to new status. Just press buttons S2 and S0 about 65,000 times until it can be programmed. My thumbs wouldn't make it, but an electronic rig could probably be built.

 

Judging by the wear n tear that I've placed on just the unlock button.... I wouldn't recommend pushing it 65k times.... I've had to get one key replaced because the unlock button got stuck.

 

Tom:
Sure, the fob is always one-channeled. Therefore, if one uses the key interchangeably for both vehicles within 256 code rolling. It should still work.
However, I agree. This is bad usability. Once a key is used for one vehicles (ECU) more frequently, it could get out of code search range (256), and it may never open the other vehicle again (needs reprogramming).

P.S. If ECU is four channeled, that means we can have up to four fobs to pair with a Prius ECU. Good to know.

 

What you might do is to have both cars programmed to accept all of the keyfobs inserted into the dash.

Then add ordinary $2 mechanical keys to your keychain. So the 2005 keyfob gets an additional key to get you in the door of the 2009, and vice versa. Or you could have a locksmith rekey the mechanical lock of one of the cars to accept the key of the other car.

The end result will be that all keyfobs work in the dash, and the mechanical keys will get you into the car that the keyfob key won't. The SKS/remote functions will only work with the car they were originally programmed for.

As for full SKS function, there might be a window of 128 usages while the car is new during which you could add a 2009 keyfob to the 2005 car. Programming the 2009 car for the 2005 keyfob is way beyond the 128 limit, if in fact that is the problem.

 

sorry you can't do that as far as I know I tryed

 

Having multiple Prii keyed alike is fairly easy. As far as the rolling code fobs go, it can be done but is not recommended, and may not be legal for the general public. Last year I did a 4 Prii set for the Deparment of Defense, where all 4 Prii had individual keys/fobs, and one master key/fob that worked for all 4. Coding a master fob does require a bit of understanding of the structure of the underlying algorythm as defined by the NSA. Unfortunately, it will also work on any Toyota that uses the same FCC ID fob. As I said before, not recommended.

Bob

 

While a bit of an oversimplification, it's a bit like master keying conventional pin tumbler locks. Every master or group makes for a lot of additional pin combinations that will open the lock.

In the case of rolling key codes, they are designed so that the consumer can't do this. As Bob points out, you have to trick the system to make it work, thereby compromising security.

Tom

 

Would it be a pain to have both cars unlock when you only want to drive 1 and you leave the other car unlocked after you drive off?

 

You could always do what some of my friends have done: remove the lock entirely.

I know it wouldn't be simple on a Prius, but it's kind of a amusing thought. I know of at least two people that have eliminated locks on their trucks. One replaced the starter key switch with a toggle switch, the other removed the pins from the lock. Theft is so low in this area that most people leave keys in their cars and their houses unlocked. Given this, it was an easy step to the convenience of no locks on the car.

As for me, I keep my house locked. I worry about you PCers finding where I live. After PCD, I now keep my shotgun loaded.

Tom

 

Where did you say you live Tom?

 

I'm not worried about you. The cold will keep you at a safe distance.

Tom

 

Oh wow! A few questions if you don't mind...

1. Does the black logo (non-SKS) keyfob use "Limited Seed" mode to prevent adding used keyfobs to a car's list of acceptable units? The Microchip HCS362 datasheet description of this sounds like what happens with attempts to add used keyfobs.

2. Is the silver logo (SKS) keyfob communications protocol a superset of the black logo protocol, or something entirely different?

3. Could you restore a keyfob to "new" protocol condition by wrapping the sync counter back to zero?

4. Does the British non-SKS keyfob use the same protocol as the US black logo, only a different frequency?

5. KeeLoq is an NSA protocol? I thought is was just a proprietary protocol of Microchip.

 

Dammit! You got me, but after winter comes ...





August!!!!!!!!!



Bloody cold here in August! Gets down to 32 degrees F some nights.
I might choose to follow the sun?