Mazda mx5 miata key immobiliser

Hi friends,
I’m wondering if any of you can help me with something…

My old merc is playing up (ironically it’s a problem with the extremely complicated rfid key system), so I bought myself a battered old 2002 mazda mx5/miata to get me around and have some fun in. It’s a great car to drive.

So the old girl appears very basic. No fob to unlock, you put the key in the door like the good old days.
Aha thinks me, finally a simple to hotwire car that I can get to start with my implant.

So I picked up a rfid 125 kHz car starting kit from ebay. All appeared well. I need to get a spare key that I can cut off and leave in the ignition to bypass the steering lock.

But lo and behold, the guy at the key cutter says he can’t cut a spare because there is a “chip” in the key for the immobiliser. I did some research but can’t find much info on what chip it is. There is no battery in the key. I can’t detect anything with 125 kHz or 13.6 MHz receivers.

Does anyone know what this chip is?

I’ve ordered 315 MHz and 433 MHz kits for my arduino but don’t expect to find anything because, from what I’ve read, these generally seem to be powered rather than passive transmitter.

Is this thing even rfid?

I’ll add a pic of the key soon but it is just an unremarkable looking thing with plastic thumb turn and simple toothed key, (like old cars in the 90s)

Any help greatly appreciated, as always.

PS security is not a concern I have with this car. I got it very cheap and I pity the fool that would steal such a wreck. Although I am going to stick a gps tracker in it just for fun.

I have a number of suggestions for you, but before I type them out, I would like to see your key to make sure we are singing from the same song sheet

Here it is.

No battery. Same both sides.


This will take me a little while to type out, and as you are on line, if you want to read through this, It will actually have some answers there for you

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Fantastic thank you.
Yep that’s the one I bought

The transponder is passive ( Like our implants )

Here is an example of your key and what is inside it

I think you have a couple of options, Since you bought the same system I used in my post, you could probably follow that to get your solution.

I removed the lock barrel on my example, but if you want to cut a key to leave in the ignition, you can do that.

Just get the locksmith to cut you a blank and tell them that you dont need the chip.
Take the new blank and put that in the ignition
Then get one of these to put your old key with transponder in.

about 7GBP from Aliexpress

alternatively, you could CAREFULLY open up you key to get the transponder and mount that over the ignition antenna, and use the key in the ignition.

Im pretty sure the lock smith is correct, but if you can’t open up your key, You could prove if it has a transponder in it, by trying the new key to start the car, If the car fails to start theres your proof.

You can actually buy a tester ( Like a DT Diagnostic card that goes around the ignition ), but they are not really worth it

About 5GBP

I think you should have most of your answers you need, but if you have more or get stuck, just sing out


In fact, that was into a Mazda also, SO with luck, the wiring colours will be the same

That’s really useful thanks.

The transponder bypass should solve the problem. I didn’t know that was a thing. I was thinking to try and spoof it with an arduino or something, but that is far simpler.

I’ll get one ordered and let you know how I get on.

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After reading a few mx5 forums I’m sure he is correct. But the only info I could get was that they are a pain in the ass when they go wrong (same as the mercedes).

I’m still curious about what frequency they are on so I’m going to have a play with the arduino anyway

134.2 kHz apparently. Same as pet tags but I assume a different standard/protocol.

I’m going down a rabbit hole again, but interesting stuff.

Thanks again @Pilgrimsmaster

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