Hi zed9 & MZ900.
Kawa Technical implied that the three sensors involved are the rear wheel ABS/speed sensor, the engine speed sensor and the gear position indicator. Code 25 is the gear position sensor.
So the diagnostics are fairly intelligent. They seem to be happy that the engine speed is ok, the wheel/road speed/ABS info is ok, but neither seem plausible for the particular gear selected. Hence it thinks that there is a gear position sensor fault. This all seems to be logical, considering that I was running at 16/41, roughly 14% outside factory optimums.
It seems likely that factory may be working on a 10% tolerance before error codes throw up. Hence either a 16T front OR a 41T rear would be within acceptable limits, but the two in combination would exceed the limits. Thats my opinion.
Thanks for your replies.