So many different directions to reset the maintenance light. Finally found the correct process for my specific model and year S60:

1. Turn the ignition to position I
2. Press and Hold the Trip Odometer Reset Button Until Mileage clears
3. Turn the ignition to position II while still pressing the Odometer Reset and hold until the triangle with the ! mark FLASHES 3 TIMES. Let go of the odometer reset button after the 3rd triangle flash.
4. Turn ignition off, then back on to confirm reset accepted.

I did this procedure while I was under the second trip odometer (T2) setting.

Give it a shot!

 

Yep. Same with all other 99 and newer cars until the new ones with the redesigned clusters