On my way back to Montana from Phoenix today and wouldn't you know it. I see a check engine light on about 50 miles in.

Pull over a few miles down the highway and check the oil. All good there. Pull out the BT OBD scanner and find a P2C7A DTC. Great. Tried to clear it, not sure I was successful. Engine light stayed on.

Drove another 650 miles to SLC. We'll see how tomorrow goes.

I'll schedule an appointment at the dealer.

Has anybody been denied warranty service for this beyond 36K miles? I'm at ~54K.

 

I’m afraid to find out the answer to that question. I’m thinking it might be an exhaust leak fouling things up. My light came on when we were in VT and the overnight temp went down to 8 °. After getting back home to NY with the temps in the 50’s the light went out on its own after a couple days. I’m starting to see a connection between the cold weather and the light coming on. As if when the pipes contract from the cold they let air into the system and throw an emissions code.

 

Well the second leg of the trip (SLC to MT) produced no check engine light. Last night I scheduled a dealer visit for this Friday. Just canceled the appointment.

I'll update this thread if the ghost reappears.

 

Well the second leg of the trip (SLC to MT) produced no check engine light. Last night I scheduled a dealer visit for this Friday. Just canceled the appointment.

I'll update this thread if the ghost reappears.

I’m having an intermittent lights on/off issue. I finally caved and scheduled an appointment with the dealer for this coming Monday. I gave them the code while making the appointment and they warned me that it could take up to three days to diagnose the problem. I thought these computers and sensors were supposed to make diagnostics easier! Anyways, not sure if any of this will be covered under the factory warranty. I’m hoping my extended warranty covers it if not.

 

Divide by 1.6 to get approx miles. I’m surprised the emissions control systems are only 3 years/60,000 kms… I thought emissions items used to be like 100,000 Km on older (late 80’s early 90’s) vehicles? I’m guessing they must have had too many failures and elected to reduce the warranty coverage (and their cost) as a result... or maybe I’m mistaken about the higher emissions warranty coverage..? They do still cover ‘specified major emissions components‘ to 8yrs/130K, I wonder what are all the components on that list exactly??

 

Divide by 1.6 to get approx miles. I’m surprised the emissions control systems are only 3 years/60,000 kms… I thought emissions items used to be like 100,000 Km on older (late 80’s early 90’s) vehicles? I’m guessing they must have had too many failures and elected to reduce the warranty coverage (and their cost) as a result... or maybe I’m mistaken about the higher emissions warranty coverage..? They do still cover ‘specified major emissions components‘ to 8yrs/130K, I wonder what are all the components on that list exactly??

I found the standard coverage and the select emissions control systems list online, question being is the DPF/SCR on the 3.0 considered a catalytic conveter? I would say yes... as it’s converting the nitrogen oxides. And for any dealer that says the NOX sensors are not covered under powertrain warranty they are FOS.

 

Update: A few weeks ago the code came back. Stopped at dealer and made appointment but after a few days the check engine light cleared. Cancelled appointment and said when or if the check engine light came back on with same code would drop it off. This happened as thought it would. Dropped of and dealer opened a "case" file with GM. About two weeks later was called that work was completed. Asked what was done. There was a hard update of the ECM, not over the air, replaced one NOx sensor, forced a regeneration cycle, and drove for about 80 miles. The check engine light and code did not come back. It has been three weeks now and no check engine light. Did notice that the DEF level indication is still as jumpy as it has been. When picked up from dealer, one segment was out, then it jumped to about four segments out. Keeping scanner in truck to read it if the check engine light comes back on.

 

Which NOX sensor is the one most prone to failure, and how does the layman know which one to replace? Rock Auto carries three, upstream and two downstream.

 

So this is nice… I had an appointment for my engine light on Monday this week. The dealer would not provide me with a loaner or arrange a rental for me. So fast forward to Wednesday and they still have not even looked at the truck. I’ve been paying three days for a rental for nothing at this point. I could’ve kept my truck till they were actually available to work on it. Enterprise gave me a Camry rental which may end up in my garage permanently. This is the third time I’ve brought this truck in with an appointment and they taken several days to even look at it. My logic is now shifting towards owning a product that doesn’t need to go to the dealership for repairs in the first place.

 

Is the truck still under the 100,000 5/yr warranty?
Have you politely gone up the chain of command at the dealer?

If it is and if you have, might be time to use the numbers in the owners manual for help from GM.

If yours doesn't/won't supply courtesy transportation and won't honour an appointment, then you need a different servicing dealer.
(no reason why servicing dealer and selling dealer need to be the same place)

 

I know this doesn't help but I would find a different dealer.

 

I did. I went to the Chevy dealer instead of the GMC dealer because they were awful as well. Maybe it’s there region we are in here in NY. The truck has 74k on the clock. The problem I’m having is because they haven’t even looked at it yet they cannot determine if it will be a warranty repair or not. My guess is if I was under 36k they would’ve easily bent over backwards to get me a rental. Oh and confirmed they still haven’t even started working on the truck yet.

 

Go pick it up and tell them to book a service appointment (date and time) that they can keep.

 

I need my damn emissions inspection. I’m overdue now and the cops around here just love that excuse to pull you over.

 

I see… that’s really sucks.

 

Took a few days to find the repair order. The NOX sensor what was replaced was the #1.

 

So update on the AT4… they still haven’t looked at it. 1) they are down techs
2) there’s an engine rebuild in progress
3) there’s a transmission rebuild in progress (I thought they swap them out these days)
4) the other techs aren’t certified to diagnose my codes
5) the manager assures me that my extended warranty will cover the rental

Stay posted everyone. Looks like we have another week of driving the Camry rental ahead of us. Might end up with a Camry by the time this is over.

 

Its back... Picked it up on Feb 25thbarely put 500 miles on it since i got it back.... this will be the 3rd time im taking it in for this code...

 

Dealer replaced my Catalytic converter. 5 days 100-150 miles no code...

 

Got the AT4 back today. Apparently it was a corroded ground wire. Didn’t hear that one yet for this code. Coincidentally the dealer had this part in stock. Seems suspect to me. Also this +$400 repair is not covered by any warranty because it’s considered corrosion. Took the truck for drive and put over 150 miles on it to make sure. The light didn’t come on so hopefully it will hold out till I can get it back over for the emissions inspection. I’m not confident…

 

was this a ground wire on the DEF injector or sensor related to the emissions system?

 

They said it was for the battery. If that was the case why wasn’t the whole truck acting weird?

 

Sounds like your dealer is bending you over… so they are saying it’s not covered under warranty because it has corrosion on it..? WTF? Who built the damn vehicle? GM. So if somethings corroded, are they not responsible (and required to fix it)??? I’d be calling the GM # and speaking to someone about it.

 

I would assume they don’t cover it cause the corrosion could be from a heavily salted area for winter and therefor it’s not GMs fault it corroded. They probably look at that more of a maintenance thing.

 

I’m wondering if it’s the ground strap that they have a TSB (which usually throws multiple codes) for corroding that’s just behind the wheel wheel liner or whether it’s the actual terminal connection up on the negative battery terminal?

 

LOL, right from the GM warranty booklet (guess not..):

 

Could a "short" in the system - or maybe a parasitic drain cause corrosion (like you'd get on a battery)?

 

So I found a guy that was saying the NORMA clamp on the exhaust is a poor design. funny enough on my first smoke test that was the spot leaking. 500 miles later with a new clamp codes back….. I am going to attempt to do the exhaust tape trick to help seal that spot. People have had luck with this and have 5000 plus miles after doing this without it re appearing P2C7A. (There is a clamp in between sensor and flex pipe, it doesn’t seal properly causing sensor to get a bad reading. Remove clamp, wrap exhaust tape around and re install clamp.)

 

 

There is a leak detector device/procedure for the 3.0.
That's not the only location that is known to sometimes leak.

 

Is there another one I should be concerned of? I don’t see to many down the line on exhaust? Maybe up on turbo?

 

I have 51K miles on a 21 GMC Sierra At4 3.0 Dmax. I had the P237a code and cleared it twice because I was on a long road trip. Came back a 3rd time at home and now its at the dealership. Service said they are ordering a new turbo. I know that is one of the points on the leak list, but did not get a straight answer whether or not they did a leak test or what the actual issue was. Service guy said that the turbo replacement is still under the powertrain warranty, and also that the the new turbo might not be the total fix. We'll see.

 

2021 Silverado 3.0L Duramax Turbo LT. A few weeks ago I had the truck in for service. Valve cover gaskets, plus another 15 or so gaskets. Coolant leaks all over the truck plus multiple exhaust leaks. They repaired it within two weeks and then had to bring in right back the next day because a tech botched up the repairs by twisting hoses(that I fixed to drive it back to them) and they didn’t seat the lower hoses correctly. Now going back in for the P1010-00 code and a P2C7A-00 code. When’s this gonna stop?

 

Hey guys,

I read through this thread as my 2023 LM2 w/ 22k miles is reading the same code. I took it to the dealer here, and the first thing they asked me, without even taking the vehicle in, was what kind of fuel I'd been using. All of our stations in the area that we use are #2. A couple spots in town have B20. The guy in service told me if we used biodiesel the fix wouldn't be covered under warranty? Even though it clearly states in the diesel supplement that you can use biodiesel as long as it's below 20%, so even if we used it, it shouldn't be an issue... He proceeded to state, well some may be labeled B20 and can have higher % than labeled...

Long story short - has anyone else with this issue been asked the same? Seems like they're setting me up to screw me.

Appreciate any info.