Below is a diagram of the EHC & EHC II self leveling suspension and it's various components. Since you have an 01...you can only have the rear SLS (EHC I) system.
Since the EHC module is below the cargo floor...make sure that it hasn't got wet (sometimes water/moisture gets in that area)...also look for corrosion on those electrical contacts as well.
Then if you see any discrepancies in suspension level...look for air leaks in the suspension components. Do you hear the rumble of the air supply system running at non normal times?