Guide to fixing your NB immobilizer.
 

How to fix/ replace/ pair your NB (2001-2005) Miata’s immobilizer.

I, like others, had my immobilizer die. I spent a long time researching, reading, and experimenting. So here is how you do it.

First, try disconnecting your battery and touching the positive and negative cables together, maybe leave it unconnected for a minute or two, touch the cables a couple times, then reconnect the battery. Try starting the car again, maybe you’ll get lucky. If at any point during this process the security light stops coming on when the key is in the on position (or when starting the car) then repeat this step. Once you start the car 1 or 2 times with the new keys and immobilizer, you probably won't have that problem again.
When the immobilizer is working properly, the light will come on and then turn off. If the light does not come on, or comes on and starts flashing again you have a problem.

Second, the original immobilizer has been discontinued, here is the new one.
Pairing procedure: https://testing-public.carmd.com/Tsb...20555/SI111866
New immobilizer/ recall: https://static.nhtsa.gov/odi/tsbs/20...52383-9999.pdf
The new part number is: BJ3D675G2L (you might want to shop around for different prices at different vendors.)
You will need to contact a dealership and ask for the “codeword” for the new immobilizer; it's an 8 digit number.

Third, you might be able to reuse your ECU (probably worth trying as new ECU’s are kind of expensive) but I cannot speak to this as I just bought a new one. You will need to find the correct part number for your car. You can look at the part number on your current ECU, or call a dealership and give them your VIN.

Fourth, buy at least 2 new keys. Here is a list of keys by another user, NW Bill.
https://forum.miata.net/vb/showthread.php?t=744564
I bought BJYV-76-2GX, and LFY0762GXB. Both worked, the old key I had for the car no longer worked and wouldn’t pair to the new immobilizer.

Fifth, I would try the pairing procedure listed above before sending your parts away. But it didn’t work for me. So I sent it to SOS Diagnostics in Canby, Oregon, S.O.S. Diagnostics - Automotive Programming and Diagnostics I got it back, and it worked!
I heard about a place in the UK called ECU Decode Limited. https://www.ecudecode.co.uk/
But I can’t attest to it since I didn’t use it. There might be more places that I don’t know about.

I will try and answer any questions if I can.

Charlie

Any chance you could re-post or upload the pairing guide somewhere accessible? Original link doesn't work. Additionally, was wondering if you could elaborate on your experience with SOS diagnostics, Did you have to send them the parts?, What was the turnaround time?, Did they just program your immobilizer and ECU? Cost?

Thanks - Tom

Hey sorry I missed this. If the links gone then I don't know that I can find it. It wasn't my link.
Sure, you send them the parts, I believe the turn around time is listed on their website so I'd refer to that for more specifics, but mine was about a week I think.
They program your ECU and immobilizer to match each other. I don't remember the cost but they'll email you back with a quote very quickly.
But my experience with them was positive, it was very simple and easy.