So... I have the dreaded error codes 172 & 181. I've done the front board test and the readings are all within 1-2 from the specs listed in the manuals. That lead me to think it's a trisensor problem. Since it was the older white base sensor I ordered a new black model with the mini flow board. I installed as listed, set the flow button on the board and it's still reading 172 & 181. My multimeter is reading all the AC and DC voltages (fairly close) as well.
I removed the cell and visually everything looks good. No build up since it was recently washed with acid.