Sorry not been on here for a couple of days. yes that would more than likely be it the only way. Of checking it if it's a crown controller would be through the dash, service mode, diagnostics, access3, inputs, then ecr1 and look to see if the counts go up as them motor drives. What drive motor is fitted?? If it's anything like the European trucks the crown drive motors have an external encoder, the earlier trucks have an internal encoder which is part of the bearing. It is a fairly common fault we have over 400 trucks on site mainly crown, jungheinrich and Still and we change quite a few each year and nearly all show the exact fault yours is showing, but on the crowns for some reason they don't always bring up an error code