Just been through the key exercise with my 380.
I lost one of the keys during a house move.
Wanted a genuine key so bought a blank from Mitsi, took it to the local locksmith for cutting. The locky couldnt program the genuine key, but they could program their suppliers key. They tried, but their system, while it could read key codes, refused to program another suppliers key. So took the key to Mitsi, and they programmed the immobiliserer and the Remote Key Entry system. Key blank $285; cutting $25, Programming $44.
Then, I found the lost key.
It wouldn't start the car nor the RKE.
Followed the instructions given here, which, is extracted from the 380 Workshop manual section 42.
Was able to program all 3 keys with the RKE function, but the immobiliser in the lost key was not matched to the ECU. Took the keys to the locky and read the codes, but they were all different, and effectively unreadable.
Took the keys to mitsi, and they did the immobiliser. Apparently they need to read the keys and then program the ECU. They did it gratis.
The chip in the key is a Philips (NXP) PCF7941, and contains both the immobiliser and the RKE function, and they are separate functions. It seems that the user can program the RKE but not the immobiliser. The chip gets its power from the induction loop around the key barrel. Why any one would want to be capable of programming the RKE but not both is a mystery, but thats how it is. Sounds to me like the system is a development of the TW series where the RKE was a separate unit, but in the 380 both functions were included in the key as a result of technical developments with semiconductors. The immobiliser code in the key is encrypted, so just what is required is a mystery at this stage. As one post remarked "WTF its only a car key"
Just for information.