LFA exhaust back pressure sensor issue

Those symptoms do sound like an exhaust back pressure sensor issue. It's key for monitoring exhaust flow, giving data to the ECU to optimize combustion. A bad sensor can mess with fuel delivery and timing, causing smoke and the warning light. What color is the smoke, black, white, or blueish? Any changes in fuel consumption or engine performance besides the smoke and light?

The smoke is blackish. I've noticed a slight drop in fuel efficiency, and the engine feels less responsive during acceleration. What does that mean for the exhaust back pressure sensor?

Okay, blackish smoke usually means incomplete combustion, so the engine is running rich, too much fuel, not enough air. The fuel efficiency and responsiveness issues back up the idea of a faulty sensor messing with the air-fuel mixture. Given the mileage and symptoms, the sensor is probably bad and needs replacing. Get it checked at a workshop to confirm, but be ready for a replacement. That will likely solve it.

Thanks for the advice. I'm booking an appointment at a service center for a diagnosis and sensor replacement. The estimated repair cost is 245€. Your help has been invaluable.