Couldn't agree more about starting with motor itself then moving to tach for the vibration. The U15 chip, like Blaze said, is probably the problem but there are two tricks to try before replacing it and putting all the parameters back in.
1-If you have a monitor, go to the floor height screen, change one of the floor heights, save it, then change it back to the original height. sometimes this will clear the fault but the chip is starting to fail its read/write ability. If it doesn't save, try #2.
2-remove the Eprom chips on DDP board and reinsert them in making sure you are properly grounded, i've seen the entire board go out when someone had their hands all over the board. If fault is still there, change chip.
Hope this helps,
All the best!