'Antitheft' warning related to a specific key

Another problem, another thread.

When we got our C3 it only had one key. Within a week, she had managed to lose it at a leisure centre: Fortunately, a kind member of the public handed it in. The near miss prompted us to buy a second 'Plip' key from Citroen, so then we had two working keys.

The new spare was put away and only used occasionally, given to garages when they had the car to do work on it.

After a while, using the original key, we started to get an 'antitheft' warning coming up on the dash display whenever the original key was used. It started and drove perfectly normally apart from that. However, we were a little bit afraid that the original key was going to fail so we started to use the new replacement key which did not give these problems.

We've now discovered that the original key has moved on to a new phase of failure - it won't start the car at all.

Normally I would assume that this was down to failure of the transponder in the key, but if so, why did the car allow that key to be used for so long before finally rejecting it altogether? I'm just trying to narrow the fault area down - has the transponder failed or has the car somehow 'forgotten' that the original key is registered with it? How do I prove that one way or the other?

SiriusHardware wrote:Normally I would assume that this was down to failure of the transponder in the key,

Yes, I would have a new transponder chip fitted if I didn't have access to lexia. If I did have lexia, I would program a new ID46 chip.

SiriusHardware wrote:I'm just trying to narrow the fault area down - has the transponder failed or has the car somehow 'forgotten' that the original key is registered with it? How do I prove that one way or the other?

You prove it by reprogramming both keys to the car again (use lexia clone tool to do this). If both keys end up working you will know that one key got forgotten. If only the new key works then you know its a faulty ID transponder chip.

The dealer did the key programming procedure with lexia when you had your second key made so they would both work with the car.

I understand about using Lexia to 'Teach' the car about both keys assuming that both key transponders are OK and the car has just 'forgotten' about one of them. I don't have Lexia and the variety of choice under that link you posted is bewildering, with quite a range of prices. I assume the most expensive ones are the newest latest versions with support for models up to the present day?

My partner likes her C3 because she considers it the most comfortable of all cars she's ever sat in, so if this one ever bites the dust we will probably just keep buying Mk1 C3s until there are none left to buy anywhere. (We did exactly that with her previous favourite car, the Citroen ZX - she owned three of those in a row). So any version of Lexia that we would buy doesn't need to support anything newer than the C3 Mk1. What are my Lexia options in that case?

The other approach, as far as I can guess, is to fit a new transponder which has the same identity as the one in the working key so that as far as the car is concerned both keys are the key it works with. But programming an ID46 chip - presumably cloning the ID of the working transponder into it - how would I do that?

Further to your problem, i have a blip key that will not lock/unlock the doors on the buttons but will start the car. I understand the key when turned in the ignition unlocks the immobiliser, so does this mean only the door switches in the key are out of action.

The C3 Plip key is unusual in not having any sort of indicator light which comes on when you press it so it's more difficult than normal to judge whether it's just the switch which is defective or whether the fob is actually transmitting but being ignored by the car.

I had to change the switches on the transmitter part of the key for an Astra 'G' when the buttons started working less and less just due to wear on the switches and cracks around the solder joints - the switches are normally only attached to the associated printed circuit board with solder, which is a very soft metal. Years and years of fingertip pressure can eventually cause cracks in the solder.

Alternatively, your problem may just be that the car has forgotten the wireless fob programming. There is usually a way for the car owner to program the central locking part of the key back into the car - I don't know what it is for the C3 but I bet someone here does, or try searching for it elsewhere in these forums.

If you have access to a UHF radio receiver (such as a scanner or a 70cm band amateur radio) which can tune to 433.920Mhz try listening to see if the key transmits anything when you press the button.

SiriusHardware wrote:I don't have Lexia and the variety of choice under that link you posted is bewildering, with quite a range of prices. I assume the most expensive ones are the newest latest versions with support for models up to the present day?

Yes, to a degree. Later versions command a higher cost. Your car is 10 years old, so any of the new lexia clones (not second hand) will work with your year.

SiriusHardware wrote:So any version of Lexia that we would buy doesn't need to support anything newer than the C3 Mk1. What are my Lexia options in that case?

the top 10 of these should work with the C3 up to, and even beyond 2009.

SiriusHardware wrote:But programming an ID46 chip - presumably cloning the ID of the working transponder into it - how would I do that?

With your lexia clone tool (its actually the car that does it for you).

alsie2 wrote:Further to your problem, i have a blip key that will not lock/unlock the doors on the buttons but will start the car. I understand the key when turned in the ignition unlocks the immobiliser, so does this mean only the door switches in the key are out of action.

I think it depends on the year. Early C3 has 2 parts in the key. One to remote unlock and one to start the car. You can have the key start the car but not remote unlock or have it remote unlock and not start (immo). Oh, and you can get them to unlock and start

SiriusHardware wrote: If you have access to a UHF radio receiver (such as a scanner or a 70cm band amateur radio) which can tune to 433.920Mhz try listening to see if the key transmits anything when you press the button.

Have a look at this topic for a plip tester as an accomplice to the lexia laptop.

SiriusHardware wrote:Alternatively, your problem may just be that the car has forgotten the wireless fob programming. There is usually a way for the car owner to program the central locking part of the key back into the car - I don't know what it is for the C3 but I bet someone here does, or try searching for it elsewhere in these forums.

This one? (Key fob reprogramming for a Citroen C3).