Thanks guys. I tried cleaning out the wheel wells etc, but to no avail. So I took it to my merry Isuzu mechanic who suggested that there is some vacuum valve that sits near the axle and classically gets plugged up after a heavy snow.
If this is so, it suggests a rahter poor design for the TOD since after heavy snow or mud drivng, TOD will go on the blink. I guess if it assumes an all wheel drive mode then that is still safe, but I wonder if we can just get under the hood and clean it ourselves?
Any ideas? Anyone verify this?