**EDIT** Have a 3.8 ltr. 05 grand caravan STX with stow n go. The check engine light has been on for a couple of months and yesterday was nice so I investigated. The only o2 sensor I found was sticking out of the top of the CAT. Going by my old Haynes manual (that goes up to 2002) and speaking with a vendor from this site today it is verified there should be a o2 sensor before the CAT as well. The one in the CAT is the 'after CAT'. I guess I'll look harder for the 'before' CAT. Seems strange that they would put one in on only one bank of the engine. The flange and Y coupler are right in front of the CAT so it appears as though that must be what they have done. Also, just so I'm straight on what all is in the exhaust system, please advise on what these things are pictured below. They are pictured in order from engine to tailpipe.

Grr, the forum won't let me post anymore pics- please see link page 5 post #45. Sorry and thanks. https://dodgeforum.com/forum/2nd-gen...20-code-5.html

 

The cat is mounted to the rear exhaust manifold and the downstream O2 sensor is mounted to the middle of the cat.

 

Yea thats the one I can see. Can you direct me to the before CAT o2?

 

If you see the exhaust manifold and the nut labeled 1, look below it and you see the cutout in the manifold sheild and the opening in the manifold. That is where the upstream O2 screws into.

 

 

Excellent! thanks very much for that. Now I gotta ask about the likelyhood of my CAT being clogged. The van has 126,545 miles on it. I have been using pure sythetic oil for the last couple of years and i do oil changes every 5000 miles. I try to run 10w40 when I can find it but sometimes use 10w30. This seems a little thin to me given the milage but it's all ways on sale and it is thicker than recommended in the manual (5w30 I think it was). Anyways, between oil changes it 'uses' at least 3 qrts of oil. The pan gasket seaps oil a little but not enough to account for this much. It doesn't smoke and seems to run great and plenty of power. Could this mysteriously disappearing oil be clogging the CAT? How could I figure this out? At a loss here. Hate to replace the CAT and not fix the cause of the first one going bad.
Thanks.

 

If it were plugged, you'd have other running issues. No power kind of stuff. Usually when you get cat efficiency codes, it's because the cat isn't performing. If you watched both O2 sensors with a scan tool, they cycle at the same rate because the cat no longer does it's thing. Maintenance wise, there would be nothing you could do to prevent this that I know of. And I believe oil weight for an '05 3.8l is 5w-20.

 

OK thanks for that. Given what you said then I think a good place for me to start in getting rid of the MIL light staying on is simply replacing the secondary o2 in the CAT. It seemed pretty unlikely to me that the CAT would be clogged with only 126545 miles on it but stranger things have happened. Thanks and I'll let you know how it goes.

 

my 06 calls for 5w 20 too,
I run mobil 1 syn and doesn't lose a drop, but you to have 40k more miles then I do,
is the reason you whent to a much heavier weight oil is due to the oil loss? or did it start using oil after you went to the 10w 40

and to help you with your posting pics see this thread, you basicly upload the pics to photobucket, then copy them

https://dodgeforum.com/forum/dodge-c...-pictures.html

 

I created an album on here which contains my pics which I thought would make posting them easier but there it no way of using those pics that are all ready up loaded- that I can see anyways. Most all my pics are on Shutterfly and they have since stopped hosting pics in these kinds of places- that really made me mad.

Anyways, yea the thought was that thicker oil won't 'go away' as quickly as the thinner stuff. I have even used a round of really thick additive from Napa with no noticable results. It'd be nice to know where its going.