Hello, my name is Rusty. Those pedals work by closing a circuit, which activates the pitch bender circuit to apply the effect. Since the pedals are close to the floor, they can get very dirty, and build up tarnish and debris.
Your specific piano can be difficult to clean in the traditional sense, but there is stuff that works very well called DeOxit. You can find it in any electronics store. Spray that into the pedal, where the contacts are, and press on the pedal about 20 times. Repeat until the functionality comes back.
Especially if the other pedals are working, you are dealing with dirty contacts. The DeOxit will clean it up.