Seat Mii Automatic Gearbox Issues

Whoa, sounds rough! I had something similar happen with my Mii (though mine's a bit older). Check engine light and the gearbox acting up. Definitely get the automatic gearbox checked ASAP. Could be the lock-up clutch in the torque converter. Does it feel like it's slipping between gears, or is it more of a shudder? The grinding noise isn't good, either. Has the transmission fluid been changed recently? These things can be surprisingly sensitive to old fluid.

Slipping is definitely how I'd describe it, especially going uphill. The grinding is more noticeable at lower speeds. Transmission fluid hasn't been changed as far as I know... Is the torque converter fault something that happens often with these automatic gearboxes? And how much did something like that cost you to fix, more or less?

Yep, sounds exactly like what happened to mine. Slipping, grinding, the whole shebang. That lock-up clutch in the converter is a known weak point, apparently. I ended up having the whole torque converter replaced. As for the cost, I'd rather not talk about it… it wasn’t cheap. Definitely take it to a good transmission repair specialist to get a proper diagnosis and quote. Don't just go to any garage; you need someone who knows these automatic gearboxes inside and out.

Well, just got the car back. It was indeed the torque converter. New one fitted, cost a bomb at 2120€, but at least it's driving smoothly again. Thanks for your help and suggestion that it could be the torque converter! Saved me a lot of stress trying to figure it out alone.