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

From reading the manual and studying the wiring diagram it seems the Motronic 4.x system actually applies a bias to sensor and reads the differece between the bias level and the other lead. Therefor, you really need a differential probe setup to read the sensor voltage.

With a scanner and your laptop, you can get a real time display of the O2 function. The 32 bit ECU in our OBD-II systems has lots of diagnostic code in it so unless your MIL lamp is on, your O2 sensor is probably OK. My car is still running on the original one in the front at 118K. The rear one was diagnosed bad by the ECU at about 90K and was repalced then.

The one I have is from Harrison R&D but there are several out there in the range of $100. They all read the generic OBD-II codes, not the Volvo EFI codes.
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'96 965 with 16' wheels at 118K. Had '85 745 Turbo Diesel for 200K.

Your O2 sensor readings indicate a bad sensor.Make sure you check it after warmup-these sensors don't work when cold.Also check for bad connections before replacing it.Let us know what happens. sredwine 94 944T,98 V90

Thanks for the info. I checked the voltage swings of the O2 sensor in my ford ranger and it operates the way I thought it would. I ordered a Generic sensor for the volvo.
Ed

I recently purchased a OBDII code reader from a company on the internet that is a pretty good one although it won't input into a computer. It was $ 119.00 and is pretty good for my level. They have better models although I don't know their prices on them. You can contact them at 800 655 4492
The company was Wharehouse Auto Parts out of Redding CA. What I bought was a Innova 3100. Since I bought a 1995 Jaguar XJ6 and it is a electronic nightmare.
The dealer gets $ 100.00 just to scan your codes (although Auto Zone and many auto parts places will scan and re-set it for free)Check them out on the internet and I am sure yo will find one in your range that will do the job.
Dennis

Thanks for the info Dennis, I'll give them a call.
Ed

I have always used an analog voltmeter to check for proper O2 sensor operation, you need to be able to see the swings since the O2 sensor is always going lean/rich/lean/rich, etc... averaging on about .5 v or so. You won't see this movement with a DVOM.

DEWFPO
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1998 S90 069,500 and 1995 964 153,010

Thanks for the info about the analog meter. After I posted the message, I got under my ford ranger to see how it compared with the volvo. It has a nice swing just like you said, so I ordered a generic 4 wire to put in the Volvo. I'll let the forum know after I replace it.
Ed