the 39 is a look back fault. the cpu checks the nts when leaving the floor. when you go in the direction of the open switch the elevator will travel at 90% of the failed switch. depending on how fast contract speed is you can deduce which switch is causing the problem. also you may have a bad relay in the net box, the relays are pulled in by the mfs switches, nts relays have bi furcated contacts. one trick that sometimes works is to pull the relay out and bang it on the floor, of course if you have some new ones by all means replace it.

If you look on some of the older posts on this forum this fault has been discussed quite a bit.

It was a bad mfs switch when u tested them on inspection they checked out but I decided to change the ones on bottom one at a time and found middle switch was bad