New to me 2015 LTZ/ PO420, 430, 2099

dna9656 · May 13

I bought this truck, rebuilt the tranny 6l80, (because it won't quit in my drive, it'll quit 1500 miles from home) 130 oddk miles. I got the PO420 and PO430 and PO2099 codes; also yesterday, I got an accelerator voltage not right code. I had the tranny rebuilder replace an exhaust clamp (it is down range of all O2 sensors) and I had it running and creepered underneath and felt around all the joints, listened for exhaust leaks, then we shut it off and hooked up the shop vac to the exhaust pipe and connected the vac hose to the exhaust of the shop vac, blowing air into the system from the end or the exhaust pipe, found/heard no leaks. The book says to check the wiring under the hood. You know that plastic tube the run wire through to protect the wrapped (with tape) wires? I felt it near the water temp sensor, it turned to dust when I squeezed it. Now, I'm no Chuck Norris so that seems like a lot of heat on those tubes. I got a bag of that stuff on hand so I will replace it. The passenger side wiring going to the injectors seems to be in the same shape, the driver's side not. The book says to check the wiring around the heads, there ain't none! I have 4 new O2 sensors on hand even though all the installed ones are within parameters as tested by my scanner. I can post the freeze frame picks; there are like 4 pages of them. I do not know enough to read them and put together a diagnostic. Do I really have to go to GM for a new Y pipe (includes the cats) or is there a equal set out there that doesn't cost so much? I see some come as a 3 piece set up; is this to ease installation, make dropping the tranny pan easier, it's cheaper because it's two less welds, or cheaper to ship? I do not understand why ONE company offers (sometimes) more than 2 (one is a 3 piece set up they other is a welded Y pipe one piece deal) models for the same truck. Can anyone shed light on this? I'm about to drop another wad on the cats and while I do not want to spend more than necessary I don't want to buy something I'll be replacing in a year or 2 or 5.

BY THE WAY! I bought a "Topside Creeper" on Amazon, a little over $200.00, I got the optional tool tray that swings out from under the cushion. If you don't know what this is, it's a ladder with a platform at the top for your chest as you lean over the grill/fender to get at stuff. It looks a lot like an engine hoist/puller/crane. I'm installing some very stiff foam on the ladder so it won't scratch up the paint. I'll post some pics. Don't buy the POS on TEMU; I did and it's a cheapie knock off, I have no confidence in it even though it's very similar in design, I think the one I bought on Amazon is better steel. it's workmanship is better for sure. I returned the stand to TEMU, they said keep it. I might for work around the house....Both made you know where.

silveradosid · May 14

you need a scanner that can monitor the maf and o2 sensors. check all intake pipes an intake gaskets for leakage, check the pcv system also. any unmetered air getting in after the maf can trigger cat codes. you could also try the sco