These LG dishwasher drain pumps suck!!!
I’ve been through 2 in about 7 years now and I just had yet another one fail on my LDF7551BB.
This pump is a little 3-phase AC motor driven by a small inverter on the control board. The inverter also monitors the 3-phase current draw to determine a “acceptable load range” of the pump’s impeller.
The pump impeller and its supporting bearings are completely mechanically isolated from the “electrical” side (3-phase windings) of the pump assembly so as to prevent leakage into the wining section of the pump assembly.
It seems that the bearings on the mechanical-side go bad and allow too much radial runout and/or thrust free play. The motor/inverter then go into a “tizzy” and the impeller then starts to either work only “sometimes”, work poorly, or in another case, not spin at all.