I own a 1995 850 wagon.
I've just noticed that the speedometer is starting to go on the fritz!
How difficult is this to replace? I'm assuming that it is electronicly controlled....

 

The plastic gears for the speedo are a common problem.

Possible source:
http://www.odometergears.com/subpages/volvo.html

 

Auto house sells a speedometer sensor...What is this for then?

 

The common thing to have happen is that the odometer quits, due to a gear inside the housing breaking. This is a very common and easy repair, thus, that's what code 33 was referring to.

From your description, I'm assuming that speedometer is not working, not the odometer. In that case, it could be the speed sensor (like you spoke about). IIRC there is no cable for the speedometers on the 850's. I bet Tech knows a methodology to test the speed sensor. - AB

 

Correct B1mmer. The speedometer works occasionally. I haven't checked the odometer, I assumed the one wouldn't work without the other.....

 

Do you have any ABS codes?