I have a general question about scan tools and a specific one about monitoring an O2 sensor.
I'm new to this forum and I was hoping someone could suggest a reasonably priced scan tool for the backyard mechanic that can be used with a laptop and will work on Volvo's.

Specific question on monitoring O2 sensors. The different documentation I've read suggests that this can be done with a digital voltmeter. I tried this and get a reading of .75 volts almost constant in the engine running state at idle speed. I then used an oscilloscope since I thought it might be pulse voltage. What i observed was that the level for the most part stayed at the .75 volt level, but there were very very narrow spikes (1-2 millisec at about a 50 millisec rate going in the negative direction to about the .4-.5 volt level. Is this the way the O2 sensor should act?
Volvo 960, 1996 - 57K miles