Its called “de-rating” by TQ, and it is by design. I received this from them in my correspondence with TQ about the motor cutting power at higher temperatures;Hi, were you able solve the problem?
I had some similar experiences with bike these days. At the moment it's pretty hot here (30C). Today I climbed around 500m in boost mode with default settings. At around 300m I had only half of the max assistance.. My input was ~200w, bike 110w to max 150w (boost mode). The moter was quite hot. After a 10min downhill full assistance was back. No error codes...
“Under extreme circumstances, derating of the power may occur. This happens in small steps and only as much as is absolutely necessary to maintain the legally prescribed maximum surface temperatures of the motor.
Derating does not affect the lifetime of the engine. The circumstances that favour derating are:
- high ambient temperatures
- high rider weight / system weight
- long and very steep climbs
- low speed, little cooling by airflow
Especially in the usual area of use of the TREK Fuel EXE (trail biking) where uphills and downhills regularly alternate, there is usually no noticeable derating.”