I just recently had to have the exhaust gasket that goes where the catalytic converter and down pipe join replaced due to it having a leak. Normally I would replace it myself but due to throwing out my back the week before I took it to an exhaust shop i've used in the past to have a new gasket installed.

After the installation the mgr who installed it said it was done and also put a sealant on it to ensure it didn't leak. So after driving the car a few miles I noticed a chemical burning smell like rubbing alcohol and figured it was the sealant they used just burning off excess. Well later on in the day after running around to a few places I came out to the car and the CEL was on and when I got home I pulled the code and found it was P0420 "catalytic converter efficiency below threshold". I cleared the code thinking it might have been caused because they plugged the exhaust a few times to double check for the leak.

It drove fine around town for 2-3 days with no issues. Then I took it out on the hwy and as soon as I stopped the car to get some stuff and came to start it again the CEL was on again with the same code.

So after reading a few threads I decided to replace the spark plugs, check for vacuum leaks, and also run a tank of premium. I cleared the CEL and I saw an improvement and the light stayed off for 5-6 days till yesterday when I took it out on the hwy again. I cleared it again and drove it a few miles and this time noticed that it was running rougher than normal and when I pulled in my work parking lot it felt like it was sputtering and you could smell raw fuel. And last night it drove rough still and I noticed when going thru a drive-thru the same raw fuel smell. This morning I started it and the CEL is back again but I did notice since leaving it on it is running smoother and no roughness at low speeds thru parking lots.

I am wondering if it is related to the sealant they put on the gasket? I've asked a few people and they think it may have damaged my O2 sensors but think my catalytic converter might be fine since it was just replaced back in April of this year.

Any ideas or suggestions on things I should try?

 

If it helps I just pulled the freeze frame information. Here is what I got.

Engine Load = 34.902 %
Engine Coolant Temperature = 185 °F
Fuel Trim Bank 1 Short Term = -6.25 %
Fuel Trim Bank 1 Long Term = 0 %
Intake Manifold Pressure = 5.511 psi
Engine RPM = 1,560.5 rpm
Speed (OBD) = 45.981 mph

 

Seems like a real high engine load.

Other than that, I would have taken the car right back to the mechanic when it poped a code later that day. That way he may have had some responsibility for the problems. Not sure if it was having any issues before you took it to them. Take it by there and see if they can help.

 

I'm kinda hesitant to take it back to that shop because they don't know anything about Volvo's but one of the tech's there I do trust with exhaust work was suppose to do it. Now normally i'm in the bay with him was unable to this time due to my back. Well after an hour passed when it was a 30 min or less job on a lift the mgr came in and said he did the work because he's never worked on a Volvo before and told me what he did which worried me.

I have made numerous calls up there with no call backs. So i'm going to go up there tomorrow morning to talk to them but i'm unsure about letting them mess with it because every time i'm there they ask me their tech questions with Volvo's and I know way less than you guys.

 

Some observations:

1. WTF would your tech put sealant on an exhaust pipe?? Very shade-tree IMO.
2. Don't see how rough running would be caused by your CAT CEL; if anything, the CAT CEL may be a symptom of rough running or something else wrong.. i.e. maybe they knocked off a connector or vac line when doing the exhaust work?
3. Where did you take it anyway? I would find a recommended indy who knows volvo and take it there; may have something else going on with the car...

FYI: here's a link that will shed more light on your OBD2 readings:
http://en.wikipedia.org/wiki/OBD-II_PIDs

Also, kind of cryptic, but found this utube informative on the topic:
http://www.youtube.com/watch?v=nJ0G01nlFRo

 

So after having it taken to a Volvo independent mechanic early this morning both O2 sensors are shot and was caused by the sealant used by the exhaust shop.

I just got back from the exhaust shop and the mgr says that muffler and tailpipe sealer would not cause O2 sensors to fail. He showed me what he used which is Permatex Muffler & Tailpipe Sealer and no where on the tube does it say it is O2 sensor safe. He also went on to state that no sealant of any kind would cause a O2 sensor to go bad. He disagrees with me totally that the O2 sensors failed because of the sealant and that he would call me and let me know if they would pay for the repair work to be done or not.

The shop I went to was Monro Muffler in Concord, NC. I would have taken it to my normal independent Volvo shop but he was booked till after Christmas and I would have done it myself if I hadn't thrown my back out.

 

Unless you can see sealant residue on the old O2 sensors, there's no way to prove it caused them to fail. Unless they had < 60K mls on them, they were probably due anyway. BTW: hope you replaced them w/OEM sensors? If not, you may be having O2 sensors problems again soon...

 

I replaced both sensors back in April when I replaced the catalytic converter and have put less than 15k on it since. I used OEM O2 sensors that I got thru FCP Groton which I believe were Bosch.

I didn't get a chance to look at the O2 sensors when the mechanic had them off inspecting them but i'm going to take a look at them later today when put on another new exhaust gasket I picked up from the dealer which was luckily open today considering it's New Years Eve.

If I get a chance i'll post pictures of the old gasket and the O2 sensors if there was anything on them.

 

So here are the pictures of the pre-cat o2 sensor and also the gasket and back of the catalytic converter which shows all the stuff he put on there.

I did attempt to clean the pre-cat 02 sensor but I was unable to get the post-cat sensor off to try and clean it but since doing that and cleaning all that stuff off the exhaust joints using 1,000 grit sand paper and installing a new gasket I am no longer getting the P0420 CEL but it is still running like crap and not as much power as it use to.

Someone suggested I should run some seafoam thru the intake which might blow the junk off the post-cat o2 sensor and run a bottle in my tank. What do you think? Or should I bite the bullet and buy all new o2 sensors?