Is it possible to reprogram a Key Fob?

[anchorage77]

Hi everyone

I wish to reprogram a second-user key fob to my car - as a spare...

I have hunted high and low to get the definitive reprogramming instructions for my car, and have read many posts, purchased info from ebay, and even RTFM ( which is wrong) so here goes....

My car is a 1997 C class (w202) it has the 3 button key fob with the metal key slid in the side (never used the metal bit) there is just a lump of plastic which make a whirry-clicky noise when inserted - and works faultlessly

To reprogram the manual sugests various key-presses involving watching lights on the mirror, which is where i hit the first hurdle, as there are no lights on on my mirror. no - the mirror is there, but it has no lights, and looks like an original mirror???

So how do I know if the alarm is armed? I here you ask! well there is a button top-middle (ish) on the dash which disables either the internal or external alarm sensors, and in this button an LED blinks when armed.

Anyway, I purchased a (used) key-fob on ebay, not conserned that the metal blade will not fit as I wont use it... BUT HOW CAN I MAKE IT WORK WITH MY CAR???

does anyone out there have the answer? ( will buy you a beer and be a friend for life!)

regards Andy

(sorry if you read this in another post)

 

[Ian Brown]

what type of key you have i dont think the three button key came out on the c class until the facelift model here is a pic of the 2 keys. pic 1 should be the key for your car and pic 2 for the face lift model

 

[anchorage77]

Its the 3 button one on the right - but without the red bit

 

[Ian Brown]

As far as I am aware you can’t re-programme the key to another car but I am sure you can programme a new one by pointing them at each other do a search for programming keys there is something on the forum about it.

 

[M6AJJ]

Sorry but I think you are on a loser. The three button key can only be programmed once to a specific car, and then cannot be reprogrammed.

 

[anchorage77]

Thanx for that, I wont waste any more time on it

 

[philharve]

Hi All

Exactly how do these keys operate (righthand picture)? I don't mean what goes on inside, I should be able to work this out for myself once I know the principle involved.

What I am interested in is what happens when the key is inserted into the lock? Is there an interchange of information between key and car, possibly using infrared signalling?

I understand the key emits a radio signal, rather than infrared, for locking/unlocking. I know this because locking/unlocking can be accomplished with the vehicle out of sight of the key, e.g. with the key in ones' pocket.

REGARDS Phil

 

[anchorage77]

Well Phil, I think it is IR as I have a key which is not for my car, and when I insert it into the ignition there are no noises whatsoever - it wont do a thing - I have dissasemled a few of these and there are RF and IR parts on the board. - I have now managed to obtain the spare key by writing to the previous owner listed on the log book