Replacement Transponder Key

MX5 Project, Jan-2022

The MX5 came with only one key fob and when I investigated the cost of getting an additional key matched to my vehicle, my cheap summer run-about was in danger of becoming a real money-pit.

A search of the various MX5 forums revealed a number of people that had successfully managed to do it themselves at a fraction of dealer prices, so decided to try that route. The forums also convinced me that the process is not straight-forward and if not done correctly you can end up locked-out of your car. I’ve tried to document the process I went through as clearly and simply as possible. Hope others find it useful.

A couple of notes: I believe if you already have two keys, you can use the car’s built-in procedure that allows users to add additional keys without the need for any external hardware/software. The method outlined here is applicable if you have one key only, or even no keys.

Also, bear in mind this procedure is for a UK-spec 2006 MX5 NC 1.8L with Remote Keyless Entry (RKE). It may not work for other variations of vehicle.

There’s four major steps in the process:

  • Finding an MX5 4 button key fob c/w working electronics.
  • Matching the new key fob to the car’s keyless entry system.
  • Get a new blade cut.
  • Matching the new key fob to the car’s immobiliser.

Finding a replacement key was relatively easy as there was a number of used keys on Ebay for around £20-£50. I got one for £22.49. Just be sure to get one that the seller says is “tested and working” and make sure to get the correct part number. My key was type SKE126-01 with Mitsubishi electronics. To find the part number you need to split the key apart (using the same method as if changing the battery) and look inside the main body – you’ll probably need a magnifying glass:

Matching the key to the keyless entry system was straightforward – there’s a procedure in the service manual that involves switching the ignition on/off three times, opening/closing the driver’s door three times, etc. It seems a bit elaborate but it works fine. The procedure flowchart is given at the bottom of this page. This gives you a key that can remotely open/lock the doors but it won’t let you start the engine.

You may think getting a new blade cut is the easiest part of the process – not if you go to Timpsons! I went to the local supermarket that has an in-store Timpsons. I asked the chap at the counter if he could cut & fit a new blade to the new fob. He rummaged through his drawers for a while and couldn’t find a matching blank blade. Then gave me a load of excuses about how difficult it is to get a new blade that made me wonder why he was in the key-cutting business. The best he could do was cut a new blade if I was able to get a new blank one myself. Hard to imagine a locksmith that couldn’t source a new blank key blade, or couldn’t even be arsed trying!

Anyway, went to a small independent locksmith, who looked at the key, said he didn’t have a blade in stock but could get one the next day. Now I’ve a new, physically fully working, 2nd key.

The most complex step is matching the new key to the immobiliser. This involves programming the vehicle’s Passive Anti-Theft System (PATS) using a PATS-capable diagnostic software package along with a suitable OBDII cable. It looked as though a commonly used tool among the MX5 community is FORScan for Windows so I decided to use this also.

You can download and use it for free but with limited functions. To access the key programming facility you need an Extended License. You can get this on free trial for 1 month and this should be sufficient to do the job. But I want to do more than just PATS programming, so I opted for a one year license for just £8.14 – which is great value considering the functionality you get for that money.

FORScan is great value but it’s not a rounded, complete product and the documentation is, at best, incomplete – you have to search on the FORScan forum to find specific “How To’s” if the subject isn’t covered in the documentation. Unfortunately, the forum allows ordinary forum members to post in official “How To’s” posted by the FORScan team which clutters the documentation and adds confusion and uncertainty.

The FORScan website has a list of OBDII diagnostic cables that have been recommended for use with FORScan software. I went for the Vgate VLinker FS USB from BMDiag in the UK. There are cheaper alternatives that might work perfectly, but I didn’t want to take the chance, so opted for the proven device.

With the VLinker cable plugged into the car and FORScan installed on an old laptop, everything worked with no hassle. Very quickly I was able to examine & clear some minor DTCs, monitor & record real-time data, and so on. To add the new key you use the “PATS Programming” function available from the Service Functions facility in FORScan.

Important Note: I firstly installed the latest version of FORScan (2.3.44, 2021-11-25) but discovered that this won’t allow PATS programming for this vehicle. This is widely reported on the MX5 forums. You must use version 2.3.4 beta, 2016-09-21, which works fine.

There’s one other pre-requisite before you can start programming the new key. The PATS programming function has security access protection. To get past the protection, you will be given an “outcode” from the PATS system and you must respond with an “incode”, which is generated externally.

There are a number of on-line services available that provide an incode generator. I used that worked fine. You need to create an account then access the generator under Services / PATS login calculator, i.e.:

Right, time to start programming the new key. With everything connected and FORScan running, new key in the ignition lock and the car turned on, select “Service Function” (the spanner icon) and look for “PATS Programming” adjacent to one of the car’s modules.

Please note the procedure below is specific to my car and FORScan version 2.3.4. The official generalised FORScan procedure can be found in this link – you should read this first for a more rounded view.

Select the “PATS Programming” function then press the “Run” button. You should now see something similar to below.

You should be told that there are at least 2 keys stored. Check that “Spare keys programmable” is enabled then select “Ignition Key Programming” and press OK. You will now be presented with the security access dialogue:

Press OK and then you will be given the “outcode” and required to enter the associated “incode”:

Use the PATS login generator/calculator identified above and obtain the “incode”. Enter the “incode” as required then press OK. The next dialogue form should be:

I already had the new key in the ignition so simply needed to switch off then on again. Then pressed OK and this happened:

You should see the number of stored keys increased by one. You can now switch off/on then cancel the PATS programming function (unless you want to add another key).

The total cost of the hardware & software was:

  • £34.99 Vlinker Diagnostic Cable
  • £8.14 FORScan License (1 year)
  • £15.00 Key Cutting
  • £22.49 Used Key

In total, that’s £43.13 for the FORScan diagnostics and £37.49 to obtain a new physical key fob. However, I don’t count the cost of FORScan as I would have bought that anyway for general maintenance & upgrades.

So the true cost of obtaining a 2nd key fob was just £37.49.

Matching Keys to the Keyless Entry System