I think I have a bad catalytic converter. Bank 2 keeps throwing a P0430. Replaced the O2 sensor, the problem came back pretty quickly. The downstream voltage on bank 2 tracks the upstream pretty closely while on bank 1 it's much steadier. Not an expert but these apparently are the classic signs of a failing catalyst. Emissions inspection coming up soon so I need to get this buttoned up. What other troubleshooting should I do?

Bought it used and the whole system is clearly aftermarket. Both sides have NGE608266 whichis the part number for an inexpensive cut-and-weld unit from AP Exhaust. I don't know why it's an aftermarket unit but it may have been a cat thief. Given the manufacturer dates stamped on the cats the work was probably done around 2023. Seems quick for a catalyst to wear out but I gather cheap aftermarket units sometimes don't last very long.

Should I get an aftermarket bolt in replacement (which I could do myself)? This would also replace the bank 1 catalyst, which is still good, but probably isn't far behind. Or, since I don't weld, should I take it to a muffler shop and have them put in another cut-and-weld?

Should I go for OEM, OEM-grade aftermarket, or EPA-grade aftermarket? What have you guys done in the past?

 

I'm in CA so I don't get a choice. You are right that the OEM grade last much longer. They are required to have 100k mi warranty. You might also be experiencing an issue that was never fully solved previously and just covered up with some new converters. Good brand of O2 sensor? No wiring issues? No other rich issues or mechanical damage?

 

I have gotten a P0174 bank 2 too lean code once or twice but usually it's just P0430.

I checked the exhaust manifold bolts and all are in place. The intake manifold is shared between both banks so I would think if it was a problem there then both banks would be affected, and they are not. It's always just bank 2. No idea beyond that. There is a bit of a sooty shadow on one of the flange bolts on the passenger side so I suppose that could be an exhaust leak? But no obvious holes due to physical damage.

 

I have gotten a P0174 bank 2 too lean code once or twice but usually it's just P0430.

I checked the exhaust manifold bolts and all are in place. The intake manifold is shared between both banks so I would think if it was a problem there then both banks would be affected, and they are not. It's always just bank 2. No idea beyond that. There is a bit of a sooty shadow on one of the flange bolts on the passenger side so I suppose that could be an exhaust leak? But no obvious holes due to physical damage.




It did have a vacuum leak when I got it, the HVAC vacuum hose was dry rotted and literally broken in half. Fixed that. Haven't checked others. PCV, Evap, what else?

 

I had the same issue with my 22 Silverado LT, a faulty catalytic converter gave me a P0420 code and was causing a rough idle, got it replaced and now it's running smooth. It was a pretty pricey fix, but worth it since the emissions techs said it was the cause of the issue.

 

O2 sensor, senses oxygen... Profound I know. But it assumes all the air getting past it came through the intake. If there is O2 in the exhaust it assumes it got there from there being too little fuel for a complete burn ... So it gives it more fuel. What's your long term trim on that bank? Full rich? Your exhaust leak might be letting air in, causing a rich condition but being reported as lean. That rich might have killed the cat, but might also have just covered it in soot that needs to be burned off. Some of those bolts don't look factory. Get some good factory style gaskets, some new bolts,/studs, put all the new stuff in, leave the battery unplugged for a while, and try the old "Italian tune-up"... At least that's what I would do. Cats are expensive.