thanks guys, after some further inquiries, i was told that the positioning system does not rely on just the encoder only, from what I'm understanding, i believe that as the car runs and passes thru the lu and ld sensor, when both lu and ld are on, a snapshot of the current position count is compared to the stored floor count. If these 2 counts are not equal within a certain count, then the car will do an emergency stop and after that i was told it may do a initialization run, or it may do a correction run, not totally sure which. however, we may be onto something, as the last call was 3 days ago, at which time i had the mechanic check the cab for any side motion, cab steadiers were ok, but he indicated that the roller guides were out of adjustment, and almost scraping rail on one side, he adjusted the roller guides. I figured it would be back, so i went out the following day and ran the car all day with no failures, so now after learning the above info, I'm wondering if maybe the sensors were getting out of the vanes and causing trouble.
could be just a coincidence that the car has not come in yet, we will see. will keep you posted. thanks sinister1, for the input on checking vane clearances