CEL came on and I got the following

443 - 3 way cat eff.
435 - Front HO2S slow response
522 - Rear HO2S Preheating
153 - Rear HO2S Signal


I'm thinking of starting with the rear sensor. Has an aftermarket cat. Any suggestions?

1995 850 NA

I usually get O2 sensors from the junk yard. Try that first, they are way cheaper than the stealer.

443 is the only code I've been getting...

It seems a bit odd to get codes that deal with three different things even if they are all related.

I'd erase the codes but hang on to them and if the light comes on again I'd pull codes right away and see what resets.

It seems from the codes the rear O2 isn't heating up as it should and it's also lost it's signal. I'd check the connector and wiring as it's odd it threw both codes at the same time. This alone might be what tripped the cat efficiency code. But getting the upstream code too ... any chance you ran over something and it caught the leads ??

Junk yard O2s are cheaper but they are used and especially for the upstream one I'd go new since the better it works the more accurate your fuel delivery and higher MPG. Depending on how used the junk yard one is it could cost you more in gas in the long run to try and save a few bucks on the purchase of the sensor.
Rockauto com has upstream O2s for $54 BECK/ARNLEY Part # 1564038

This is the second time the light has come on. It takes about 200 miles to come back on. Last time I think it had the following codes

443 and 435.

I lost the paper so I am not positive on this. I guess I will find out again in a few hundred miles.

Are the front and rear sensors themselves the same with the exception of the wires?

For another car I had you could get the same OEM sensor but without the pigtail connector for significantly less money. Does anyone know the OEM O2 model number?

Thanks

If you call a Volvo dealer they will give you the part number.

As for Junk yard sensors... My bet is that they are only a couple of years old at worse. I usually pull a few and see which one has the most surface rust on it and which comes out easier, in an attempt to find sensors that have been replaced withint the past few years.

I think most long term Volvo owners that try to hang on to their cars usually use the dealer to do repairs, maintenance, etc. I haven't found ANY after market sensors around here and none that I've used have effected my gas mileage in any way. Maybe bettered it. I constantly monitor my gas mileage so I would know real quick.

Alright

CEL just popped up again today

The winning numbers are...

522
153

Clearly something is wrong with this sensor, weather the wiring has been damaged or the sensor its self is bad.

Can the O2 sensor voltage display on an OBD2 scan tool with these cars? I don't have one because I have never owned an OBD2 car before. But I am considering one of these tools, maybe one that hooks to my laptop.

Yeah, I have this one. It is very handy diagnostic tool. These have their limitations; you must remember that what you're seeing as output data, is at best a low resolution digital sample of an analog signal, especially for trying to monitor the sensor when conditions are rapidly changing, like viewing the O2 sensor during acceleration.

That being said, I don't go anywhere without it. I have used it more than once to help diagnose odd problems that did not set a code.

I have an Innova too

But I would reconsider that if I could have picked up one of the Actron CP9580 units because they have a built in "it could be this or that" library built into the unit so it's a bit handier doing diag in the field where you don't have access to a computer to do research on the codes.
It's sold under a couple of different names.

Both those scanners look great. They have really come down in price the last few years. I'm a cheapskate though. I ordered one of those $20 Bluetooth ones that connects to my Android. I wanted something that could plot my O2 voltages and this claims it can do it.

I'll let you know how it works or doesn't work out.

Also, I have a friend of mine pricing me out a rear o2 sensor through their sources. In the mean time I am going to look for any damage to the wiring.

That is pretty sweet.

Remember that narrowband O2 sensors are limited in what information they can give you; their range of sensitivity is centered right around stoich. Sort of like having a speedometer that only tells you exact speed from 30-40 MPH, and whether you are above or below that range. Short/long term fuel trim is generally more useful for diagnosis of existing problems, because that tells you what the ECU is doing to compensate. Also, O2 voltage is not constant - the full signal would form a sine wave. Any data you could graph would be incomplete, the best you could get would be to take an average, which should be right at stoich. Otherwise there should be a set trouble code. Sorry if I'm rambling, I like this subject. :P

I can't blame ya for picking one that uses some tech you already have, and is way cheaper. I'm sure it will serve the purpose.

I want to compare the front O2 sine wave to the rear O2 sine wave. Sometimes you can judge the condition of the cat. Additionally, it might give some warnings signs of a faulty O2 sensor.

Anyway, I probably wont see much of any sine wave right now. I think I found my problem. Some how one of the wires got pulled out. Strange thing is, about 100 miles prior to the CEL coming on I had taken the car in for an alignment...

That'll do it.

Well, let us know what kind of data you're able to log. I'd be surprised if you plot the data and see a wave appear, as I understand it there's just too much communication lag.