Try this:
1) Turn the Power ON
2) Set trip meter to "ODO"
3) (you may need to Power OFF at this point)
4) Turn the Power ON
5) Hold down the ODO/Trip button for 10 seconds
6) While keeping the ODO/Trip button down, put the driver seatbelt on.
7) You will see b_on / b_off choice in the ODO meter, make your choice with the ODO/Trip button
Drove me mad on my RX300, went off if I unclipped too soon just before reversing onto the drive.
Thanks for trying Rob. Unfortunately your procedure does not seem to work on my car! Perhaps I should have explained that my car is a brand new March'07 registered RX400H.
Does anyone have any further ideas? Thanks.