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CAR KEY TRANSPONDER.

cicero

Oct 18, 2021
3
Joined
Oct 18, 2021
Messages
3
Hello, Recently I mislaid the second key for my car, I have now found it but it got me thinking about how this system works. I have found that the electronic part of the key can be taken off the key. I have started my car and then removed the electronic unit from the key to some distance away and the car engine keeps running so it only needs this part of the key to start the engine. The batteries in the key went flat some time ago and were removed so the key no longer works the doors etc. I assume that the electronic part of the key gets power from the wire ring that goes round the ignition switch then sends a return signal to the computer. As i used to be an electrical engineer and a radio amateur I am most interested to get more knowledge about this. I am now 84 so the knowledge that I have is a bit out of date. I am well able to build radio gear including transmitters receivers etc and my aim is to build a small unit that can replicate my car key but I do need more info. I know that one of you reading this will have that knowledge so please share it with me. There is a bunch of wires that go from the ignition wire ring to the computer so again I assume that the signal from the wire ring goes to the computer down these wires. I will get an old ring from a scrapped car and will open it up to see what is inside. Please do not tell me that I should not be doing this as I have no intention of using the information for any other reason but for curiosity.
 

Delta Prime

Jul 29, 2020
1,966
Joined
Jul 29, 2020
Messages
1,966
There is plenty of information online.
It would not be ethical for me to tell you how to hack the security system.
I believe it is against the law, replicating and or
bypassing security measures design specifically by the manufacturer of the vehicle.
Your intention may not be malicious.
Your curiosity for educational purposes is commendable. But this is an open forum... anyone with
"ill will" we'll see this information as well.
Therefore... make model year of your vehicle. The information provided to you will be a regurgitation of a textbook on how the system works.
 

kellys_eye

Jun 25, 2010
6,514
Joined
Jun 25, 2010
Messages
6,514
The component part of the key that allows the car to start is similar in function to the 'tracker' devices they inject into pets. It consists of a coil that takes energy from the transmitter (in the key barrel of the car) to power a low power transmitter to return the 'code' to disable the security that prevents the car being stolen.

Many people remove this 'tracker' device and simply glue it to somewhere close to the key barrel - with a few inches of it - and this allows you to use ANY key (that you can have cut at many stores that do that sort of thing) with the same profile as the physical key you have. In this way you can have as many keys as you want/need without the cost of replacement electronic versions. My Jeep stealership quoted £150+ for ONE replacement key fob........

Note that using this method disables the theft protection circuitry and should your vehicle be stolen by a 'screwdriver thief' your insurance won't cover it.

This 'tracker' may be in the plastic part of the key (can you see any different coloured parts to the plastic?) and measures some 2-3mm across and 5-10mm long. They look something like this:
 

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Bluejets

Oct 5, 2014
6,922
Joined
Oct 5, 2014
Messages
6,922
Getting your version of the rolling code to work should keep you busy for the next 100 years.
 
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