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Yes just tried the key on it’s own same warning and just turns over
That's useful information. What I suspect is happening is car is unable to read the transponder in the faulty key. The way the system is meant to worK is: - There is a coil which is wrapped around the ignition switch which couples magnetically to the keys coil using a 125kHz signal. The key's transponder is powered by this 125kHz signal so even if the key's battery is flat it shouldn't stop the car from starting.

What I think is happening is that key's coil is not connected properly. The machine the locksmith uses was probably more powerful than the cars system so was able to read the transponder. I think it would be a good idea to have a look at the key's PCB with a magnifying glass or loupe to see if there is a poor connection to the coil. Alternatively, it could be worth contacting the locksmith again and explaining the situation.
 

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Discussion Starter · #23 ·
That's useful information. What I suspect is happening is car is unable to read the transponder in the faulty key. The way the system is meant to worK is: - There is a coil which is wrapped around the ignition switch which couples magnetically to the keys coil using a 125kHz signal. The key's transponder is powered by this 125kHz signal so even if the key's battery is flat it shouldn't stop the car from starting.

What I think is happening is that key's coil is not connected properly. The machine the locksmith uses was probably more powerful than the cars system so was able to read the transponder. I think it would be a good idea to have a look at the key's PCB with a magnifying glass or loupe to see if there is a poor connection to the coil. Alternatively, it could be worth contacting the locksmith again and explaining the situation.
Cheers will do worth a go thanks for all your help don’t know what machine it was it’s the one they use to code the keys and they charge £70 for doing it but in my case didn’t do it as there both have the same already
 

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Discussion Starter · #26 ·
Can I ask if I buy the coil will it have to be recoded as if it is I may as well just pay the £70 at timpsons for them to recode a new one
 

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Can I ask if I buy the coil will it have to be recoded as if it is I may as well just pay the £70 at timpsons for them to recode a new one
Despite the description it is just a simple coil. The actual transponder is in one of the two Integrated Circuits on the other side of the PCB. You should be able to see two tracks at each end of the coil. The tracks will couple through some vias (plate through holes) to the other side of the PCB and then to the IC.

The coil is soldered to the PCB and can be removed with a small soldering iron or a suitable heat gun. If you use a heat gun you must make sure other components are shielded from the heat and don't get too much heat. However, before you spend any money on this you should make sure the coil is faulty. It just a long piece of wire so should have a low resistance (about 2 Ohms) between the two ends.
 

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Discussion Starter · #28 ·
Hi
Really at a loss there’s no visable signs of a break there’s continuity in the coil so really don’t know what to do with it if anyone has any other ideas I can try don’t want to try coding it myself and end up with none working and according to timpsons the keys already have the same code so not sure why ones not working
 

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I think there must be something wrong with key's security IC (e.g. PCF7941 datasheet ). The IC should be doing the same function as a ID46 (PCF7936AS)
transponder chip. I suspect this part of the IC is not working properly. I suggest you go back to Timpsons and tell them what’s happening and see if they are willing to sell you a £70 basic key and guarantee it will work.

Edit
This is worth reading because it mentions the process of cloning keys with ID46 chips. Unless things have changed since this article was written cloning keys with ID46 chips requires a visit to the car. Understanding Cloning - And How It Can Work For You - Locksmith Journal
 
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