The security system consists of the key(s) programmed with their unique code, RF transmitter which sends the keyfob code to the BECM,, the BECM which has the unique keyfob code and unique engine ECU code in the case of diesel models, the engine ECU which has a unique code on diesel engines, a transponder on the ignition switch assembly which also prompts the keyfob to transmit it's code when the key is inserted. Additionally there are various sensors including internal movement detection and switches on doors and bonnet to detect opening and the microswitch on the drivers door lock assembly (Gav's favourite) for entry of the EKA and sensing when the door is unlocked/locked.
Intermittent immobilisation is usually caused by spurious signals from exterior sources...plenty about that on the forum, which is usually cleared by the EKA procedure. It can also be caused by the code in the BECM becoming corrupt and the BECM not recognising the "Rolling Code" sent by the keyfob, this is usually cleared by unlocking the BECM and clearing the Armed/lockout status and clearing the RF memory buffer. Another cause can be repeatedly pressing the fob buttons whilst away from the car.
Then there is a faulty fob (Rare) and engine ECU losing it's code which will cause immobilisation..more prevelant on diesel engined models.
If the system has gone down hard, the EKA will not work and the BECM played it safe ....armed & locked itself out then it's either a trip to the Stealer for a new BECM or one of the independants for the BECM to be unlocked and reset.
I am not at a loss on the P38 system, as others have written on here and I hope that this clarifies the systems operation without going into too much jargon. There are plenty of posts on here covering the topic which repeatedly crops up with air suspension faults, overheating and water loss etc. etc.
Are people really sifting through the related posts on the subject???
Methinks they just put up a new post without doing the research and probably finding the answers or enlightenment.