Re: All the key questions. (archive)

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: someone at E46 board said that even the wallet key has the chip that prevents thefts. My q is then -

: 2. more importantly, if all the keys have the chips, how would key #2 know what the last code setting was when I turn the car off with key #1? Doesn't the system work by the car and the key programming a certain code, then next time the codes must match between the two? How does key #2, or #3 know what that last code was??

Lots of questions in the attached thread. I will try to hit the high points - with what information I know.

There are identification chips in all keys. Lets assume for discussion you have the 4 standard keys (2 master remotes, 1 Valet, 1 plastic spare).
All these keys are coded by BMW to work with the security unit that is in "your car". They will not work with any other security unit.
Each key has a different "identity code' that is recognised only by your car.

AND - there are two separate security processes in this issue.
- identification of key to allow car to be started.
- identification of a remote key to allow remote key functions.

There is a small induction ring antenna imbeded into each key. This alows transfer of data between the key and the car when it is in the ignition - there is a corresponding antenna ring in the ignition switch. This part of the function is powered from the ignition switch part of the antenna - induced magnetic flow - same way a smart card works when you hold it up to a reader for secure entrance to a building, etc.

If the security system in your car can not read an authorized code from your key then it does not give the signal to the DME that allows it to start the car. Removing the battery and circuit board from a remote key just reduces that key to the same functionality of the plastic spare key.

As far as I know this portion of the identity code for each key for your car does not change on each use.

Now lets talk about the remote keys. When used in the remote mode they communicate with the car's security system by radio signals. Now a completely different set of security codes comes into play that relates only to the remoting capabiliites.

Each remote key works with it's own set of security codes, and it does not care what is going on with another remote key.

The remote keys have to go through a separate "initialisation" process. When this is done the car's security unit selects a "code word" for each key ( a randomly chosen number from a base of 2 to the 48th.) This code word is transferred to the remote key and is also remembered by the car for that key. Each key has it's own randomly chosen code word.

Now each time you hit a button on a remote key the code word is incrementd by one number in it's series. So the next time you use that key with the car it is expecting to see the next higher number. Since you might hit a button away from the car it tracks a series of numbers and will resync the key & code if it is within a certain range. If you hit a button often enough away from the car to get outside the expected range, then you will have to hit a button twice before the car will resond - and then put itself back in sync for that key. There is another higher range (1000 strikes) that if you go beyond that the car will not respond and you will have to re-initialise all the remote keys - they then start will new code words again.

So essentially the car keeps track of the "code word series" of numbers for "each remote key".

And that is how they can use the remote keys to trigger "memory functions" for each key.

Because BMW owners like to have a grip on things - well maybe - I like the big key with all features in one unit. I hate those other keys where they have to give you an extra remote unit - like they could not figure out how to put it all together.

But really there are also other reasons. They wanted a remote that has buttons that are large enough to control by feel, without easily hitting 2 buttons at the same time. They also want buttons that are a bit hard to push to prevent accidental operation (my neighbour often has her trunk open - happens when she puts keys in purse and closes the purse)

You also need room for a battery that will last a while, and that has the power to run that radio transmitter to give you a decent response distance.

Remember this is the first version of the integrated key. There is another one coming that is supposed to be smaller, have more capability for memory features using an embeded 386 chip, and I understand it will not have a battery but will have some other storage device that is charged by power transfer from the ignition switch coil.

While on the subject there is another unit comes into play. To prevent scanning of your system there is a blocker circuit on the car that if the car receives 10 consecutive incorrect code words from a remote, then it blocks the receipt of all signals (even correct ones) for the next 15 minutes. So of all the millions of possible code combinations a scanner only has 10 chances every 15 minutes. Not very likely. On top of that - even if they monitored your car while you used the remote to lock it. If they figured out the next code word in the sequence they would also have to figure out the "unlock" command. Not very likely.

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