4F8A Transmission Error

[weiln12]

Hey all, back again with another problem. Last week we were driving out to Denver and had a problem headed up I-70 outside of Vail. We were just moving along nicely, but when I went to downshift and pass the transmission slipped twice. RPM's jumped to about 4K both times, then it went into limp mode. We took it to a dealer in Denver, and they diagnosed the 4F8A code. They said it was a one-time code, and to just monitor it but there was nothing wrong that they could see. They said the fluid was fine, and generally gave it a good bill of health.

However, research I've done is not good regarding the 4F8A code. It appears that over time it will get worse before eventually I'll need a new transmission. If possible, I'd like to avoid this. I don't buy into the whole one-time issue thing.

My first thought was a failing solenoid, or an issue with the mechatronic. From what I've been able to find, this could be the situation. Some have replaced the mechatronic, others just the solenoid. Is there any way to identify what could possibly be causing the problem as there is a big difference between replacing a solenoid vs the mechatronic.

The vehicle is an '08 135i convertible with 73K miles on it. I don't feel like I should be having transmission issues yet, but given the problems we've had in the past 5K miles it wouldn't surprise me. We don't race or drive it that hard at all. It's my wife's DD, and she wanted it because it's a convertible and has nice toys, not because it's fast.