The Megane II uses a rolling code immobilizer system. The NT8222A communicates with the UCH (Body Control Module). If the battery goes flat or if the ECU is swapped without reprogramming, the car will start for 1-2 seconds and then cut out. Fixing this requires rewriting the immobilizer data (Virginizing) or synchronizing the VIN/Key codes—a process heavily reliant on correct x84 communication.
You turn the ignition on. The rev counter doesn't move, the speedometer stays at zero, and the digital display is blank. Alternatively, every single warning light (Airbag, ABS, SERV, STOP) illuminates simultaneously. The NT8222A is failing to broadcast the "wake-up" signal to the instrument cluster. megane ii x84 nt8222a