Can you decode car key fobs so they do not work?

Can you decode car key fobs so they do not work?

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ajg31

Original Poster:

1,455 posts

214 months

Tuesday 18th March 2014
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My GF has just had a key stolen from her car, a Citroen C3.

The last owner replaced the ECU with another C3 one which came with another key. The original key was only used to open the fuel filler cap and open colse the car.

Is it possible to get the original car key removed from the car's fob memory? At the moment the thief will have acess to the car whenever they want.

I am presuming that Citroen will be quite unhelpful as it is not the original ECU.

Thanks in advance smile

motomk

2,166 posts

251 months

Tuesday 18th March 2014
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Key stolen was the one that can open the fuel filler and doors only?

ajg31

Original Poster:

1,455 posts

214 months

Tuesday 18th March 2014
quotequote all
motomk said:
Key stolen was the one that can open the fuel filler and doors only?
Yeah, it was. I have no idea why the "new" key fits everything on the car except the filler tank though.

ajg31

Original Poster:

1,455 posts

214 months

Tuesday 18th March 2014
quotequote all
WeirdNeville said:
Do you still have an 'original' or master key for the ECU?

Generally speaking, it's pretty easy to code keys to ECU's providing you have an original key: Most cars I've encountered (Impreza, current Pajero) you can put the car into 'coding' mode ususally with jumpers on the ECU and then code away: This will code all keys present during the coding to the ECU, even if it's only one, and any not coded will be excluded and no longer work. It does rely on that original key to 'handshake' though.
Hmm, here may be the problem. As the ECU was changed I think the key was recoded to that ecu?!? Still doesn;t explain why the fuel filler cap needed a different key (which handilly also had the credit card sized plastic on it with the key code on it.


NBTBRV8

2,063 posts

215 months

Tuesday 18th March 2014
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Normally yes. The dealer codes the remote out, but obviously the key will still open the car if it is all in one. However it shouldn't start it.

ajg31

Original Poster:

1,455 posts

214 months

Wednesday 19th March 2014
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Yeah. I was being a bit dumb before and have thought about it overnight smile

The key that was stolen does the front door lock (it only has 1), auto lock/unlock via remote and the filler cap. That was obviously the original key.

The key we have left does the ignition and lock/unlocks the doors via remote. I will presume that they swapped out the ecu and just did a simple activation of the new key to allow the bsi (?) brain bit allow it to open and close doors.

It would seem that I require a full key set, locks, ignition, ecu and bsi unless anyone can work out another way? Don't fancy spending $1500 on a full set just so we can have a car someone else cannot open!

Would it be possible to get the bsi, door and filler cap with key and program the key I already have to that? I am not to cluey how these parts talk to each other

NBTBRV8

2,063 posts

215 months

Wednesday 19th March 2014
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I don't understand your question.

The dealer can code the remote out so it won't unlock the car and won't start the car. However the key will still open the door (but probably set an alarm off) and it will still turn the ignition, but won't start it.

The only way to get around the above is to make your car look different i.e. put new plates on it, or replace all of the locks so they can't open the doors via the key.

ajg31

Original Poster:

1,455 posts

214 months

Wednesday 19th March 2014
quotequote all
NBTBRV8 said:
I don't understand your question.

The dealer can code the remote out so it won't unlock the car and won't start the car. However the key will still open the door (but probably set an alarm off) and it will still turn the ignition, but won't start it.

The only way to get around the above is to make your car look different i.e. put new plates on it, or replace all of the locks so they can't open the doors via the key.
I have found out that the dealer cannot remove any of the remotes as it does not have the original ecu, and as the replacement was not done at a dealer if they try to reprogram the keys the car will become a non movable paperweight as the ecu now fitted to the car will not accept the original car program when they try to reflash it.

My only option thus far is to buy another ecu, bmi, tranceiver and barrel.

When I first posed the question I did not have all the facts, so sorry for that.