both o2 sensors, not a vacuum leak

SkyVolvo · Post by **SkyVolvo** » 13 Apr 2010, 21:12

Agh - I had this fully written up when my browser seized.
Okay, so toward the end of Feb. I bought a '94 850 Turbo Wagon, 212k on the odo and 180 on the engine. It gave me no problems for a few weeks except a smell of exhaust in the cabin - I completed a PCV job and that smell seems to have gone away.

Then it threw two codes - 435 (Front O2 Slow Response) and 443 (Cat. Conv. Efficiency). My understanding is that the cat. code comes via the rear o2 sensor - so, codes from both o2 sensors. Around the same time the codes showed, I lost turbo boost.

I did the PCV job and got everything back in place. Along the way, I became intimately familiar with all of my vacuum hoses, which are all properly connected and in acceptable condition. I've checked them again several times, listened for any hissing sounds, and then sprayed some carb. cleaner around today to check again. I feel I can rule out any obvious vacuum leaks.

After reconnecting the battery following the PCV work, everything ran normal for about a day. Around 60 miles later, the turbo boost stopped working on me again, and about 40 miles after that, the CEL came back with the same two codes.

The car seems to run fine - it's quiet and smooth. I knocked on the cat. and it seems to be solid. Somebody in another thread mentioned that getting both o2 codes can indicate a MAF problem. I'm not getting any MAF codes, but would cleaning that be an appropriate step? Or did I somehow, strangely, just have both o2 sensors die on me? They certainly look old enough.

And would this problem have any effect on the turbo, or is that more likely unrelated - like, say, a BCS?

SkyVolvo · Post by **SkyVolvo** » 13 Apr 2010, 21:25

I should add that about a week before I bought it, it passed emissions without any trouble at all. According to the computer, I'm getting about 19-20 mpg - it seems like I should be getting more, as it's more highway than city.

Post by **jblackburn** » 13 Apr 2010, 21:37

Around 60 miles later, the turbo boost stopped working on me again, and about 40 miles after that, the CEL came back with the same two codes.

It sounds like as soon as it notices "hey, something's wrong" it cuts back the turbo boost. Then once that condtion stays present, it later triggers the check engine light.

I notice less turbo boost when my car is running with the check engine light on, but even with the MAF disconnected or the light on for other reasons, the turbo's presence is still there somewhat.

You've checked for vacuum leaks, and you don't have any other fuel trim codes for it.

I think your problem is that the front O2 sensor is dying on you. This will set codes for the rear one too, if it notices a too-rich mixture coming through because the front one's messing up. I'd try replacing that front one first, your gas mileage is certainly low if you're doing more highway driving and not a lot of hill-climbing and that could be one of the adverse effects of it.

In a mix of 35-60 driving up a lot of hills, I manage between 20-22 mpg if the comparison helps at all.

Post by **wheelsup** » 13 Apr 2010, 21:39

I thought I responded to this but I guess not. Mine just threw the exact same codes. I am going to swap in a good front O2 sensor and see if the problem resurfaces.

jonathanS70 · Post by **jonathanS70** » 30 Apr 2011, 15:23

Hi guys I was hopping I could get an answer to my all day troubleshooting! I have a 155K miles 1999 S70 GLT, last week I replaced the fuel filter and cleaned, cleaned the ETM, and the MAF. Car ran great! This week I decided to take on the PCV change, I got the kit from FCP and started with the detailed procedure posted here. Got everything wrapped up today and the car idles terribly and puffs of black smoke come out of the back. I took the + cable off twice and let it re set still no change. On the 99 s70 the fuel rail has to come off to get the intake off, i thought maybe I got some dirt on the injectors so I ran the car on the highway got home still no better. I spent a lot of time trying to make it better and now its worse, and I still get air out of the dipstick tube which was the reason I started the project!!!! Yes I cleaned the PTC as well, I checked all the lines everything is tight no obous screw ups.. What can it be? Also No codes!!

Post by **bronxnativ** » 30 Apr 2011, 15:37

jonathanS70 wrote:Hi guys I was hopping I could get an answer to my all day troubleshooting! I have a 155K miles 1999 S70 GLT, last week I replaced the fuel filter and cleaned, cleaned the ETM, and the MAF. Car ran great! This week I decided to take on the PCV change, I got the kit from FCP and started with the detailed procedure posted here. Got everything wrapped up today and the car idles terribly and puffs of black smoke come out of the back. I took the + cable off twice and let it re set still no change. On the 99 s70 the fuel rail has to come off to get the intake off, i thought maybe I got some dirt on the injectors so I ran the car on the highway got home still no better. I spent a lot of time trying to make it better and now its worse, and I still get air out of the dipstick tube which was the reason I started the project!!!! Yes I cleaned the PTC as well, I checked all the lines everything is tight no obous screw ups.. What can it be? Also No codes!!

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