Seat Mii Engine Power Loss

Reduced engine power and an error code points to a few possibilities. The check engine light is a general warning. You mentioned a fault code – do you know the specific code number? That would help narrow things down. You say 'likely' cause – have you had chip tuning done previously? Did the error show up after this chip tuning?

The code is P0299. And yes, the chip tuning was done about a year ago. It ran fine until recently. Could the car computer really be the problem after all this time?

P0299 indicates a turbocharger underboost condition. Given the history of chip tuning, it's highly probable that the tuning has caused long-term stress or corrupted the original car computer settings over time. While it ran fine initially, the increased stress can eventually lead to component failure or software glitches. I suggest taking it to a workshop that specializes in car diagnostic and ideally has experience with de-tuning or re-flashing car computers to their original factory settings.

Took it to a workshop. They confirmed the chip tuning was causing the issue. They reflashed the car computer. Cost me 180€, but the engine issue is gone. Thanks for your help.