Re: 'Master' key questions

Hi Adam,

How's things?

I've done my usual and took a couple of days off the rest of the
work that I should be getting on with and

had another glance over this immobiliser thing, hence my recent post.

I've purchased a lockset that includes a master key and transponder
and 3 'normal' keys. Two of these

'normal' keys are the new Alfa type with the built in alarm remote.
They can be spilt apart to change the

battery which also means I can see the type of transponder that they
are using - and it's the same one as

the master key!?! Obviously then, something else has been written
into the memory of the master key to

make it 'special' and also contain, either directly or by some
mathematical function, the bypass or

emergecy code that you were describing. I have an ECU set and master
key from EBay (as you know) and the

chip in that key is the same as your picture. The new keys I have
are also the same except for being the

latest version (PCF7931AS). That chip is now discontinued and the
datasheet is no longer available for

download but I've made a request for it anyway.

I had always been under the assumption that the codes for ALL the
keys for the car were stored in BOTH the

main ECU and the immobiliser ECU, but, last night I discovered that
this is not the case. The

immobiliser certainly stores all the car's key transponder codes but
the main ECU only has the master key.

When a key is used to start the car the immobiliser ECU checks to
see if it is valid, if it is then it

sends it's memorised master code (encrypted) to the main ECU. If
that compares correctly to it's stored

value then the car will go.

I share your goal to find a way to reset both systems to use a
different master key, especially as I do not have one for my own
car. I think the next reasonable plan of attack is to examine the
immobiliser ECU's eeprom and then try loading/unloading different
keys into it to get a feel for how the data is stored, but for that
I'll have to go and buy an EEPROM programmer :( .

Keep up the good work I know you're doing and I'll try and answer
your emails/posts a bit more promptly - mind you being the lazy
b*stard that I am I wouldn't count on it ;)

Cheers

Guzzi

 
Received on Fri Aug 12 03:27:10 2005