This is another "old" topic but I figured it would not hurt to summarize what I did for the benefit of the community.
My car came with two keys. However, one of the keys was the red valet key, which does not have a boot release remote button and does not open the glovebox and the boot . So I always wanted to get an extra "regular" key for peace of mind.
Moreover, the alarm fuse was pulled and the alarm (and remote locking/unlocking functionalities) was not functioning. I do not care much about the alarm but I wanted the convenience to remotely lock/unlock the car and the boot. I did some debugging but because none of the remotes that I had was working, I could not use the remote re-learn trick (lock-unlock the car several times until it stops operating the lock and then quickly press all the remotes to pair them with the alarm ECU).
Therefore, I had to (1) duplicate my "regular" key and (2) reprogram the alarm. The final product unfortunately was not as "clean" as I wanted because I ended up with three different keys and non-integrated remotes but at least now I have a fully functional spare and all keys have functioning remotes!
The keychain was tailor made by an Etsy creator. I will be happy to hook you up in case you want one made (I edited the 4200 profile myself).
So, on with the details.
First, duplicating the key. To open the car and start it, all you need is a blade cut to the right shape and an immobilizer chip cloned off a working key. I ended up getting a blank key from member @Andrew1211
who made a blank 4200 key out of a Granturismo key fob (the electronics is unusable for the 4200 and I understand also the blank blade is different between the two cars). However, if you go to a good locksmith I am sure they can source something compatible for you (perhaps without Maserati insignia though). Since Andrew already did the legwork I found it convenient to simply get the key from him.
For the duplication, I went to a local locksmith with my original "regular" key and he cloned it in a few minutes. In case you have the tools, the immobilizer uses chip ID46 if I am not mistaken. I am not sure about the key blade.
As for the alarm, reprogramming it requires special tools which as far as I know are not common. I decided to ship my unit to Abacus Alarm UK as their price was more competitive than ECU Doctors here in the States. Abacus was a pleasure to deal with, and the turnaround was very quick (not considering the international shipping times).
Unfortunately, Abacus discovered that my regular key fob electronic board was toasted and this is why I had to buy a remote fob also for my original key. That was a bit of a bummer as I had hoped to have a fully functioning stock key. Unfortunately, Meta (the alarm maker) does not make the electronic board any longer, so the only alternative is to buy a used key and hope that the electronic board is good for a transplant. Current pricing for used key is too steep to justify at the moment so I just added a key fob remote.
For Abacus to re-program the alarm, I had to send the alarm ECU and the key fob electronics (one of which turned out to be faulty as I explained).
The alarm ECU is under a panel on the passenger left side. Since I have not seen good descriptions for the 4200 I will show some photos here of the process.
First you need to remove the rear seat back. Procedure for this is documented in the thread below and in many others.
Hello all, I wanted to share my experience with installing an aftermarket radio in my new-to-me 2004 Coupe equipped with the optional auditorium system. My situation was a bit unique as the previous owner had already removed the NIT and installed a tablet in-lieu of the head unit. Also, he had...
Next is the trim above the speaker. This is held by clips and you need a hook trim tool to be inserted on the left side (there is a small access cut) to take it out. Place some electric tape to protect surfaces. Simply pull out to undo the clips.
The trim will expose three screws. Take them out and slide the top panel up, forward, and out. The panel has two tabs at the bottom, mine were taped with paper tape. Not sure if this was somebody else hack or stock.
With the top panel out, you will have access to three screws that hold the bottom panel in place. Be careful that the screws have a small metal sleeve that can easily fall off as you take them out.
The lower panel has two clips at the bottom that you have to pull out. You could remove the seat bottom for easier maneuvering but you don't have to.
Now with everything out you can finally take the alarm ECU off. Sorry I did not take great photographs but it is straight forward. You remove the three nuts and then you slide alarm ECU from underneath the panel (you have to slide the three studs off the panel, down and then out, as the ECU is bolted on a bracket that incorporates the three studs that you see protruding in the photo below). The black component that you see in the photo I think is a motion sensor or something to that nature. Its bracket will come off as well but you don't have to do anything with it.
Once you get the reprogrammed ECU back from Abacus Alarm you simply plug it back in (I did it with the battery disconnected but I was not given special instructions) and the remotes will magically start working again!