How do I?
 

How do I re-set the Service Reminder?

How do I turn on the winter driving mode on the trans? I know that it is right next to the econ/sport switch. I've pulled and pushed on it in every direction and it won't move. What does it do?

The service reminder could be reset using the OBDI plugs under the hood. After that was removed, then it was no longer possible to reset it without dealer tools. OBDII scan tools that I have won't reset it.

Volvo still provides owner's manuals at volvocars.com. Winter mode is a push button. If it doesn't move, it's probably got a spilled Dr. Pepper in it acting as glue. The owner's manual does a surprisingly honest job of describing winter mode:
* In position D, the gearbox starts in 3rd gear and changes up to 4th gear.
* In position 3, 2nd gear is locked and there is no change up to 3rd gear.
In position L, 1st gear is locked.
* These positions always offer the kick-down function.

Some article at Auto Repair Technician Home talk about service reminder reset

what year is your 850? In the 93-95s you can do it via the OBD1 diagnostics port. Check out volvotips.com for instructions