Sounds like you are on the right track for troubleshooting. Unplugging parts of the system or components one at a time is a recommended method.
As for error codes related to electrical issues, I'm not sure any tubs offer that handy feature but it sure would be nice. Tripping the breaker every time sounds like an easier situation to resolve than some that have the intermittent or occasional trip.
If it's truly the circ motor only you are isolating, you might have pinned it down. Check wiring and connections for anything new or strange, loose, wet ? Then see about amp draw or test for a short.
