Hey out there. I've been watching this forum for a year or two and everybody is great. A lot of great advice. Ill try to be brief. I own an 09 wrangler jk unlimited. Ive had it 8 yrs now. Thankfully it didnt come with any gremlins. Ive been doing reg maintenance for a jeep now 11 yrs old. I just replaced both cats and all 4 oxy sensors. (Sensors from advanced auto) . and I've heard you're supposed to put Mopar sensors in because ones from Advance could malfunction or possibly go bad shortly after install. But the engine light went off after Full Repair. About two months later the engine light came back on. Flange bolts needed tightening. So i tightened & Engine light off. A month later engine light comes back on and spark plugs are bad and a malfunction in coil pack. New coil pack. New plugs. New wires. And Engine light goes off. A month later engine light back on flange bolts need a tightening again but I realized the threads were stripped, which is why the nuts wiggled loose and light kept coming on. So...New flange bolts. Now everything is great and engine light goes off. Two weeks later engine light comes back on. Now I'm getting 0420 emissions low efficiency in bank 1. And small leak 0456 I think . I change the EVAP module regulator thing on the EVAP unit. My guess at this point is there is crack somewhere before upstream sensor causing a small leak & throwing the code. Or perhaps the downstream oxygen sensor is bad. Not sure how to test 1 oxy sensor. Although I sprayed liquid wrench on the flange bolts and may or may not have sprayed residual spray on to the oxy sensor. That's another guess. Anyone?

 

That P0456 is a pretty common code and is usually remedied by checking back near the gas tank. There's a plastic nipple that has a tendency to crack or break and thus you get that code.

As far as catalyst efficiency- you did mention advance auto sensors but as long as they're not Bosch, you may be ok considering that light isn't always on. What cats did you go with?

 

Regarding P0456, mine was caused by a crack in the right angle bend in a vacuum line right by the battery. The line is under this component (red arrow) and is easily damage by heat from the engine. Bear in mind that I have dual-batteries, and this shot was actually during a week-long power outage when I was using my Jeep to keep my reef aquarium powered and the battery isolator had failed. So, there were some temporary wiring mods to support basically using the Jeep as a generator.



As for your cat problem, when I got my first error code, it kept coming and going. I replace all four oxygen sensors with Mopar parts. And it kept coming and going. So, installed a Mopar cat and that fixed it. I do know what you mean by those flange bolts, and recommend to anyone removing their cats to always install new hardware there.