I don't recall seeing any posts about this previously. We have a '14 base AWD. A month or two ago, we got a code for catalyst efficiency. Given the age and miles (~180k mi), I want overly shocked. It cleared and has come and gone sporadically since. Then, this past Saturday my wife said it was making an odd noise when she was driving and it sounded like she had a decent exhaust leak.

Sunday, I start the engine and start looking around to figure out where it was coming from. Eventually I see that the nuts between the rear catalytic converter and exhaust are gone, all 3 of them. There is significant rust and the flange on the exhaust side isn't in great condition. I couldn't find any M10-1.25 nuts locally on Sunday, so picked up the correct part from the local dealer on my way home last night, installed them, and problem solved (for now).

Has anyone heard of nuts just falling off the exhaust like this? Based on what I saw when replacing them, it appears that the threads just corroded off as two of the three studs came out when trying to get the new nuts on and I had to clean up the threads and coiled metal came out. I'm hopeful that just putting new nuts on fixes it, but it doesn't look to be too costly to repair if I need to replace that short section of exhaust, assuming other things don't fall apart from rust during disassembly. I'm also curious now if the catalyst efficiency code we got was just a precursor from an exhaust leak we couldn't hear, affecting the O2 sensors. Time will tell on that.

 

That's not surprising considering you're in the salt belt of New England like myself. As long as you do not see anything that looks like an intential mark trying to remove the catalytic converter (i.e. saw marks or blow torch marks), I would chalk it up to rust getting to it. With 180k miles and being 10 years old, thats a great life for the original exhaust.

 

Nope, no cut marks or anything. The odd part for me, it seems that the nuts are distorted thread lock nuts. I see no way for them to back off without the threads themselves from failing. The studs were still good minus old threads and rust caked on. The flange is in rough shape, but still strong enough to reseal once the new nuts were tightened.

 

In that case I'd just assume it was wear and tear. If the issue is solved then you should be all set for a long time .

 

My 02 RSX did that and the Acura dealer replaced the flange and nuts around a decade ago. (also in New England)

 

So, it's been nearly a month since I made the fix and put the nuts back on the exhaust, and since then, there have been no repeats of the catalyst efficiency code. If anyone get a catalyst code, maybe just peak under the front end and make sure all the bolts on the exhaust still have nuts. It was about 2 months between the choice showing up and the exhaust leak rearing its head.