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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’m looking for advice testing and fixing stored and permanent codes. Truck is a 2013 Serria 2500 6.0L Vortec with 283737 miles. I have P0420 P0430 and P2097 codes using my live data I see both upstream and downstream sensor are fluctuating high and low is that defiantly saying the cats need to be changed ? Also P 2097 bank 1 high limit keeps coming back trying narrow down cause I will attach photos of freeze frame when code occurd some live data photos thank in advance

Short version: 2018 silverado 2500 6.0 intermittently misfiring on bank 1. Holes 1/3/5/7. Changed 02 sensors, plugs. coils, catalytic converters, spark plugs. Once the truck is above 1300rpm or so, it doesn't misfire at all. Cannot seem to find any relation between whether ambient temperature is hot or cold or when engine temperature is hot or cold. Long version: Hey Y'all, I bought a used 2018 Silverado 2500 with a 6.0 L96 "G" about a month ago. Used from a sales lot. 160km (100,000 miles.) After driving about 200 highway miles or so, I was at a red light, and it was idling (burbling and chugging) a little weird. When I went to leave the red light, the engine was a bit hesitant, but once above 1200rpm or so, it drove fine. Over the next few days, It did the same thing intermittently and ended up throwing some codes: P0420: Catalyst system low efficiency P0137 H02S Circuit Low voltage sensor 2 P2097 Post catalyst fuel trim system high limit bank 1 P2099 Post catalyst fuel trim system high limit bank 2 P0300 random/multiple misfire. However, once rolling, it performs fine with no drama. The dealer gave me a 2 year unlimited mileage powertrain warranty through a 3rd party company. The warranty company does not pay for diagnostic work, just part changing and part cost. In order to get this warranty, I agreed to do oil change/spark plugs/air filter. For peace of mind, I ordered new 02 sensors (2 up 2 down) 8 new plugs (stock replacements) ignition coils and ignition wires. Once the parts came in, I got underneath and changed the 02 sensors. It looks like they had been changed at some point because they were aftermarket sensors. I started the truck up and cleared the codes. It ran fine for 10 minutes. I had my fiancée come out to back the truck out of the garage (I was filthy) and as soon as it went in reverse, it started idling like dog sh** and stalled out. I started it up again and we coerced it out of the garage. At this point I was tired and cranky (up for 24 hours with 12 hours of work in there.) I was in no mood to carry on with working on it. I took it to a shop and we plugged the Gucci Snap on scanner into the truck. It showed it was misfiring on 1/3/5/7. All bank 1. Bank 2 was fine. The mechanic/shop owner and I decided to have the coils/plugs/wires changed and see what happens. He called me later that evening and said the truck was running like a top. He had his datalogger on and it hadn't recorded a single misfire. I went to the shop and saw the truck had been running for about 40 minutes without recording a misfire. Drove it 10 minutes to a friend's house and had dinner. It worked fine. No idle or low RPM acceleration issues. When I left his house, I let the truck run for a minute and it started repeating it's prior behaviors. Did some studying at youtube university. Added a 2nd ground off of the coil harness to ensure it was grounding properly. No change. Cleaned MAF and throttle body, no change. Called some friends that are smarter than me. We concluded it may be the catalytic converter. While the truck wasn't short on any power.. It was a company truck (seemingly well maintained) that likely idled a lot. There are nearly 7000 hours on the truck. Not sure if that's high hours for the mileage. Took it to an exhaust shop and asked them to determine if the cat was pooched. They called me back and said it was. I did not ask how they determined this. Ordered a new set of Magnaflow cats (and a muffler for fun sounds.) Had them installed yesterday. Picked them up from the shop and the truck ran great. Today, it started doing the Harlem shake again. I'm guessing after this... It's got to be a wiring issue? Chafing somewhere? What makes me have a hard time believing it's electrical is that it is strictly RPM related. Idle to about 1300/1400 rpm. And intermittent. Once I'm cruising it's fine. If I am at a lower speed and the trans is in a gear where the RPM is low... it will (very seldom) struggle a little to build RPM. I've been using the gear selector a lot to keep the RPM's above 1400. I cannot seem to find a correlation between when the engine is hot/cold etc. If any of you have some insight, it would be greatly appreciated. This weekend a friend and I are going to hookup datalogger to check fuel trims, and also watch for misfires while wiggling harnesses and such. Have a great day! I'm about to lose my mind. This has been a slow process

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.