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So I think I have finally resolved an interesting issue with my '12 3.6/8spd. Last spring the CEL/MIL came on and it was a p0420 emissions code. My regular mechanic recommended we take it to the dealer as emissions are under extended warranty. When I got home, the light was off and stayed off for weeks. It eventually happened more frequently, usually only for a few short cycles so I never got it to a dealer as I was travelling a lot and my wife was mainly driving the Dart. When it started to come on for longer intervals I took it to a reputable dealer and the adviser found both a p0420 and p0430, which are banks 1 and 2 emissions low efficiency codes and could be due to O2 sensors or cats. He told me that IF there were no noticeable performance changes, to wait until the light was on was on steady and to bring it in. It wouldn't hurt anything but it would make it easier to diagnose if the code was active. Finally, in November that happened and I took it in. They had it for 3 days and couldn't figure it out. The O2's reported the correct voltage, and they thought failed cats would be noticeable in the exhaust, and it seemed normal.

Eventuallly after another visit they got authorization to replace Bank 1 Cat and O2's on both sides. I picked up the car and the invoice said they replaced "left side cat and O2". I got about 20 miles and the light came back on. After checking it out and reading a p0420 error, it turned out that Bank 1 was the right side! They explained the regular technician, that I had spoken to who did the diagnosis and seemed to know what he was doing, was out for a few days and a different tech worked on the car, and apparently he didn't know left from right! They then replaced the correct side and O2 and things have been great for about 300 miles.

Here's the thing that fixed. I have complained on this forum that when I drove in the cold performance was noticeably poor. It was noticeable below around 50 degrees F, and it labored below 40. I live in San Diego so temps like that are rare, but on road trips, I could tell that as temp changed it got worse and improved as it warmed up. I thought maybe I messed up the IAT on my CAI, but that wasn't the case.

However, since getting the repair I have driven in temps as low as 28 during our recent cold snap and that issue doesn't happen anymore. Performance is even across the temp spectrum. Any idea what was going on? It's only been a couple weeks so I'll see if this holds up.

Also, one of the service advisers said they had only replaced cats like that on one other car that he could remember recently, and he thought it was a 2011 Challenger 3.6. Any other 3.6 drivers out there have similar issues or hear of them?

I don't know if this is helpful but I thought I would at least put the issue out there incase anyone else comes across it.
 
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