handicare / minivator 1000 problem?

Hi
I bought and fit a second hand stairlift for my nan. All was working fine until I aent the lift right to the bottom, the sliding rail moved more than expected and the chair went into the floor. I atoppes immediately and sent it back up, now the lift is showing both code 4 and 6. Ive read everything I can find online which points at the footplate switches. Ive had this off and all wires are still connected to the switches. Ive checked for continuity from the main pcb and followed the wiring to each switch in that circuit and all seem fine. Im not sure what to check now. I know.its something silly as.it was working fine. Any pointers would be appreciated