Under EU On-Board Diagnostics (OBD) regulations for Euro VI heavy-duty vehicles, what occurs if the driver continues operating the truck with an empty AdBlue tank or an intentionally disabled SCR system?

1. The engine control unit (ECU) triggers an emissions warning, logs an indelible OBD fault, limits vehicle speed to 20 km/h upon the next vehicle stop, and severely derates engine torque (up to 40%–50% power reduction)
2. The truck switches automatically to run on engine oil without any performance loss
3. The vehicle stops immediately on the highway within 5 seconds
4. Nothing happens; AdBlue is purely optional for vehicle operation