Passive tone controls have a very limited effect, little more than rolling off the treble. They are also thoroughly non-linear, i.e. turning the knob through 50% of its travel may have 100% effect or it may have Nil effect ... I've had plenty that were virtually on/off switches. And sometimes, especially on cheaper basses, they may have no effect at all due to the quality of the components used.
My solution is simple. I hardly ever touch the tone knob on a passive bass.