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I have a 2016 Sierra 1500 with the 5.3L engine, 111k miles. About 6 months ago I changed the spark plugs & wires and one of the wires accidently got pulled out by the stupid long bolt in the steering shaft that run way to close to one of the spark plug wires. The truck misfired but I was only a few miles from home. I limped it back, realized the problem, plugged the wire in and all seemed good. Unfortunately, 10 miles later the check engine light came on again, this time just showing P0420 code (catalyst efficiency below threshold, Bank 1). I changed all (4) of the O2 sensors, but the code came back after 10 miles. I then bit the bullet and changed the drivers side cat with a aftermarket weld-on from rockauto, nope. I then paid a muffler shop to replace the passengers side cat (generic) and fix my sad welding on the drivers side. The light stayed off for about 50 miles this time but as always came back on. I then tried to put a spacer between the 2 rear O2 sensors to pull them out of the exhaust stream, light on after 10 miles. I even tried plugging the old 2 rear o2 sensors in the wiring harness and just zip tying them to the frame so they were breathing fresh oxygen, but still the light! My mechanic is out of ideas and suggesting taking it to the stealership and having them replace both cats again with the OEM setup for @$2000. I have almost zero faith that will solve the problem and that it will just be more money that I don't have going into the trash, and the dealer will just shrug their shoulders. Any other suggestions of things to look at/try before jumping off that cliff? I am a backyard mechanic with just a basic OBD2 reader. I do know that all (4) O2 sensors are putting out voltage, but really don't know how to interpret that data.

I have a 2014 GMC 1500 with a 5.3L. I recently replaced my CATs because I was getting the dreaded P0430 code. SO I put new Magnaflow exhaust systems as well as brand new sensors in it. I got it all in and about a day after I got it all installed I got the same code P04030. I double checked the seals and sensors and looked at the live data and it all looks on the level...the only other thing I can think is that there is a wiring issue with it...the connector on bank 2 sensor 2 looks in order so I'm a little confused as to why I'm still getting this code other than there is a ground or an electrical issue I haven't looked at.

Hi! In April, my Yukon was throwing codes P0172 P0175. Local GMC dealer in Louisiana "fixed", by replacing some sensor. Traveled to PA, codes came back on. Local GMC dealer fixed by replacing BCM, body control module in June. Now my check engine light is back on! Power train Warranty ran out 2-3 weeks ago. Also had extended warranty, which also ran out at 5 years, which was Sept. Code onstar says its throwing now is P0430, all of the codes from I can find are related to exhaust system. My question is are these 3 codes related??? Could this be something they will have to fix under warranty, given it's related and has been worked on several times? If not, what does this mean? Catalytic converter bad? Help! My husband is being laid off in the next week. So, obviously finances are tight. Yes, obviously itll be fixed regardless, just trying to plan and cut back elsewhere if needed. This has been a great vehicle! As luck has it, trouble starts when warranty runs out. Really wanting to trade, but waiting on new body Adding mileage if matters, 91K

I have a 2008 GMC Sierra with the 5.3 liter engine. I hear a rattle coming from the underneath of the truck only at 1000-1500 RPM’s. I checked for loose clips and stuff but I have found nothing. It doenst affect the way the truck runs just the sound. Also, the temperature doesn’t affect the rattle.

I don’t know if you all remember me or not. About a month ago I posted about my Yukon misfiring terribly. I fixed that thanks to your expertise and now I have a couple other small issues. Number 1. I keep getting a P0430 code. I’m pretty sure the right side cat is bad. When reading the O2 sensors. The graph shows identical readings for the upstream and downstream sensors. I’m pretty much resigned to the idea that I’ll have to replace the cats, and found a new set for a decent price. Still I was wondering if any of you could recommend a good set. I can’t weld, so I’ll need to buy the whole assembly. I (think I) have some time on this because I don’t need another emissions test for over a year, but correct me if I’m wrong and if this problem is actually more urgent than I think it is. Second, and more importantly, I’ve got a squeaky wheel. I tried to diagnose it, by jacking each wheel off the ground and turning it manually, but nothing happened. I checked the CV joints and brake pads in the front, but after a really bad experience when I was younger I won’t mess with drum brakes, so I don’t know if something is up with one of the rear drums, and the rear axle doesn’t have CV joints. The noise seems to come from the front driver’s side wheel. So, if the CV joints and brakes seem fine does that mean the bearings are going bad? Is replacing them possible without an impact wrench and a hydraulic press? Could I just pack them and hope for the best? I’m going to do a little more trouble shooting and update the thread with any new pertinent info. Thanks, Eric

I'm posting this in a few different Chevy forums in the hopes of getting our story heard and getting some kind of useful advice or even just feedback. So I apologize if you have already seen this somewhere else. So I'll TRY and keep this to somewhat of a minimum, but no promises. Thanks for reading all the way through if you do. I just need some feedback and/or advice. My husband and I went down to our local Chevy Dealership and traded in our old worn out 03' Dodge Ram on 12/20/16 for a 1 owner 2008 Chevy Silverado 1500 and paid a little over $16k. LOVE this truck. It's gorgeous, all the fancy bells and whistles, (On-Star, XM, remote start, tonneau cover, etc.), seems very well taken care of, and doesn't have super low miles but seems about average for an 08'. The previous owner had bought the truck brand new in 2008 from this Chevy Dealership and had brought his truck for ANY service to this dealership. So they had all the service records. So we felt good about that. When we bought the truck, we were obviously aware of the current recall on the Takata airbag inflaters and it hasn't been fixed yet, obviously. The truck did have a light on for the airbag and the Chevy Dealership told us it was for the SDM Airbag Module. They said they would not be fixing that because there is no current recall for the SDM module in this truck. And he's right, there isn't. I searched the VIN on GM and no recall for the SDM module. So with that being the only issue (besides the Takata inflators) we decided to buy the truck. Here is what has happened since the night of 12/20/16. When my husband was signing all the paperwork for the truck, it also included signing up for On-Star which was done right in the office. As my husband started his drive home with his new truck, he got an email from On-Star for his new account about 5 minutes or so after he left the dealership. As most of you probably know, On-Star does diagnostics on any vehicle they have in their system and will send the account holder a report of their diagnostic check. So he read his diagnostics report and it indicated that there was an issue with the trucks emissions. That was all it said. Something we were not told about by the dealership and at this point in time there was NO check engine light on the truck. Our salesman was out of the office the following day, Wed. 12/21, so we couldn't get a hold of him until Thursday. Late Wednesday night I tried to remote start the truck and it wouldn't start with the FOB (remote start will not work with the CEL active). We started the truck with the key and that's when we noticed the check engine light. Not even 48 hours after we purchased the truck. We called On-Star and they told us the code is P0430 which is Catalyst System Low Efficiency Bank 2. Which is an O2 sensor or the cat. When we called the dealership and told them what was going on, it took them at least a week to get the service manager to call us back and get the truck in to test the code. OK so took the truck down to the dealership, service manager tested the code and came back out and told us it read as the EVAP Vent Solenoid and that the valve flap was stuck open and causing a vacuum leak. Told us that we should have been smelling gas fumes. No we have not. At all. Never had a problem with ANY fuel issues at all. Of course we thought that sounded a little odd. My husband is not an idiot when it comes to vehicles and from what we've researched online, P0430 is a VERY specific code to the catalyst system. But of course we TRUSTED the dealership and their service manager. Maybe they knew something that we didn't about Chevy codes. So they said they would call us to schedule an appointment to have it fixed. About a week later (this past Thursday 1/5/17), we took it in to get fixed and we drove away with our loaner. Next day, we pick up the truck, service manager said they replaced the solenoid and the check engine light was off. He also told us that the problematic EVAP Vent Solenoid they replaced had no power to it and that when they took it off, the wires were crossed. How the hell does that happen..? Obviously wires don't just cross on their own. So it must have been replaced in the past by some dingle berry that couldn't figure out where the wires go and the dealership didn't have any service records on the truck for replacing the EVAP vent sol. OR that was just a flat out lie. We were past thinking this was odd. At this point, everything that had happened since we traded in our Dodge for this truck and they only gave us $100 for our Dodge to refusing to replace the SDM module to the back door locks working intermittently after a couple days to giving us the run around about getting it in to get fixed to shotty service records about not knowing if the SDM module had or had not been replaced even though they had records that the previous owner had brought it in at least 3 separate time because of the SDM module light..honestly, I never felt good about this deal when they only offered us $100 for our Dodge. It was a worn out work truck but it was worth way more than that. I didn't want to do it. I never felt good about it and always felt like we were being played. But it was my husbands truck, I wasn't there when he bought the Chevy so it wasn't my choice. I trust my husbands judgment 100%. FAST FORWARD TO TODAY 1/10/17. The truck had been in the shop this past Thursday and Friday. It is now Tuesday and my husband was out in the truck and called me to tell me THE CHECK ENGINE LIGHT CAME BACK ON! He called On-Star and SURE ENOUGH, it's P0430. Same. Exact. Code. Hence the title I wanna drive the damn truck through the front of the effing dealership. He has called the Dealership about 5 times already and of course, no one is available. Not our salesman or anyone in the service department. Go figure. Only thing to keep in mind is we bought this truck USED and was classified as AS-IS sale. We knew that and were fully aware. BUT we are 100% certain that the definition of AS-IS does not include them make us FALSELY believe that the truck did not have an emissions problem, or ANY problem other than the SDM module. They specifically told us the only issue the truck has is the SDM module. The way this has worked out (On-Star emailing the diagnostic report literally 5 minutes after leaving the dealership, the code was already in their system) they HAD to have reset the check engine light on the truck probably when they brought it around for my husband to test drive it. They did not disclose that to us. They led us to believe the truck was in GREAT working condition and had we known about the emissions problem, we could have better a BETTER more ACCURATE decision on buying this truck. Or we could have negotiated the price and getting it fixed before deciding if we still wanted to buy it. They disclosed everything except for this emissions problem and the back door locks. And NOW even after they said they "fixed" it, the check engine light is back on which makes me think they just fed us a bunch of BS and they just reset the CEL light again to shut us up and stall us until we can no longer return the truck, imho. Buying AS-IS means you know EXACTLY what you are getting. We were deceived. Hands down 100% I believe they were completely deceptive and knew exactly what they were doing when they sold us this truck. So I'm not really sure if I actually have a question. At this point, my husband is already getting the phone numbers for Wells Fargo, our financier, for GM Corporate offices or complaint department who ever we need to call there, for the Attorney General of PA, and whoever else we need to contact. Unfortunately, they aren't BBB accredited so that's not an option. Any ideas, Thoughts, advice, similar stories, feedback for me?? Anything would help us figure out what we are going to do. Sorry it's SO long but THANK YOU so much for anyone that actually read the whole thing and is willing to give me some kind of feedback. Much appreciated!!

Hello, I have a 2005 Silverado LS Crew Cab 4wd 5.3L V8 and need to replace the Cat. The truck was originally a California truck (I live in Wisconsin). My question is if I buy to whole cat system I can get a non-CARB compliant system for like $250. Will this fit/fix my vehicle? I am not sure if, because it was a California truck, the emission system is coded differently? Thanks, Jim

Before you get all judgy I didn't want to remove them let me explain Today I went to a exhaust repair shop, my truck (2010 Silvetado LT 4x4 Crew Cab - 5.3L) was doing some weird noise that I though it was related with the exhaust, I was thinking it was a leak. They checked and told me that my filters were obstructed and because of that my truck wasn't accelerating very good and could cause damage to the manifold gasket and even worst. So they tell me that they will remove them and weld a straight pipe so the air can flow normally and I can gain all the power back (keep in mind that at that moment I hadn't realize those "filters" were the catalytic converters) after that I decided to install a muffler to improve the sound a little bit. So they finished all the work I was happy with they sound, after leaving the shop the check engine light turned on and I hear the same sound coming from the manifold. I went back and they told I need to replace the exhaust manifold gasket wich I think is okay because my truck is on 150k mile range. So here is my real question: Is my check engine light on because of the gasket? because of the CC? or both? Keep in mind I'm from Venezuela, nobody here care about emissions and about fuel (I can fill my empty tank with 0.60$) my problem is with the CEL and I'm ordering a set of manifold gasket to replace them. Thank you for your time and help.

I have a 2007 chevy silverado 1500 5.3 motor two wheel drive. The driver side Catalytic Converter starter riddling pretty and now miss firing codes on computer. I found out its a dealer only part in california. Just trying to get information on a unversal cat for this truck. Not really worried about the o2 sensors.Thank you for any help.