Hi that generic fault code is for the transmission shift 2-3 solenoid. It is an electric part of the transmssion. A proper BMW scan tool would be best for diagnosis of this issue. The warning light you saw In the display is for transmssion failsafe mode. When this happens it locks the trans in 3rd gear. That's why it was driving slowly at low speeds.

The first thing to check is the fluid level. Low fluid can cause weird faults. This needs to be done with the vehicle on a lift since there is no dipstick.

Another issue that can cause this is an overcharging or undercharging alternator have the voltage checked, it should be 14v. If this stuff is ok or the fluid smells burnt the clutches Inside the trans are slipping and it will need a replacement trans or a rebuild. bimmaster40145.3194707523