The fan will always turn with the engine, although it might not be fully engaged, depending on the temperature.
When you stop you engine, the fan should continue to turn for a spin or two. Once stopped, it should turn almost freely if you push it with your finger. (A very slight resistance is normal). If it is stucked (jammed) and does not turn by hand, it is shot.
I would not mix Toyota/Mercedes. if it is defective, replace it.
JackD