Fluence gearbox issues

I had similar symptoms on my Fluence. That transmission oil temperature sensor can cause a heap of trouble when it goes bad. When the sensor gives the ECU bad info, it messes with the transmission's shifting strategy. Have you noticed if it happens more when the engine is cold, or during hot days? It's like when you have a bad thermostat in your house, the heater just goes haywire.

Interesting. I haven't really paid attention to the temperature when it happens, but I think it might be more frequent when the engine is warm after driving for a while. Could it be that the gearbox oil level is too low even if it looked ok?

It's certainly possible that the gearbox oil level is low, even if it appeared fine during your check. Especially when warm the behavior can change if the level sits just below the minimum. These sensors can be quite sensitive to fluctuations. Given the symptoms, the best bet is to visit a workshop. They can properly diagnose the sensor and oil level and replace/refill as needed. Better safe than sorry - you don't want to totally fry the transmission; fixing that gets expensive really fast!

Thanks a lot for the insight! I took it to the workshop, and they confirmed it was indeed the transmission oil temperature sensor, and also the gearbox oil level was too low. They replaced the sensor and refilled the oil. Repair cost was 365€. Seems to be running smoothly again! I appreciate the advice!