Denny NWO

My truck hasn't acted up since January and not at all with the GM live data logger so I returned to the dealer at the end of March and they removed it. The service manager said all the others that were having issues stopped at the same time as mine. He thinks it was a fuel issue, they switch between summer and winter gas up here. Will have to wait and see what happens in the fall.

It stopped acting up. sometimes flutters on start up and immediately recovers but it has not high revved since the second live data logger was installed.

It's been a week with the monitor connected to the OBDII and connected live with GM TAC and my truck has not revved to 3500RPM but has coughed and fluttered upon starting but it recovers immediately. I was told to not mark the event until it revs. The Polar Vortex brought the temperature here to -30 to -38 without the wind chill and i think the colder weather doesn't amplify the issue. Temps are back to normal but after reading Transients post from San Diego, I guess temperature is not the issue. I know a co-worker with a 6.2L AT4 always starts his truck with his remote and didn't realize his truck had the same issue until he went outside to listen to it start with the remote. GM knows it's only happening to the 6.2L engine, there are now 7 in my area with the same issue according to my dealer. I will let everyone know once the issue is identified.

Update: I got a call on Tuesday afternoon from the dealer, apparently the box wasn't communicating with GM TAC. Dropped the truck off Wednesday morning and they gave me a new loaner to drive, then I received a call at the end of the day that they were still working on the issues and needed to keep it. Got another call Thursday at noon, GM TAC is shipping a new data box so I picked up my truck and will have to bring it back next week. I did find out that this issue is specific to the 6.2L engine only and they now have 6 other 6.2L owners experiencing the same issues. Stand by. So by the time they finally figure something out, just how much engine damage has occurred by then? High revs on a cold engine can’t be a good thing. Edited Tuesday at 09:24 PM by BigMick2020 Yes BigMick2020 - I'm definitely concerned about engine damage when the truck goes to 3500RPM for 10 seconds from a Cold Start. Engine oil is not pumping very well at -29F which is the forecasted overnight low this weekend.

Update today: My truck keeps asking me to install an update every time I shut it off today. Called the service manager and asked him if I should do the update, he said to ignore it. He called me a few hours later and told me the box is not communicating with GM TAC and now a have to drop it off at the dealer again tomorrow morning. When I got home tonight, I shut the truck off and opened the door and got out, but the radio stayed on. I went back out 8 minutes later and it was still on. The FOB was in the house so I got it and went back out, reached in and pressed the start button (without the brake) and pressed it again and it finally went off.

So I took the truck to the dealer on Friday and had the box installed. It is connected to the OBDII port and sitting under the drivers seat and a black cord with a red button is sitting in my cup holders. I was told to press the button if it acts up when i start it. I parked the truck outside at home with overnight temperature at 5F ( -15C) I started it Saturday morning and it went to redline for 4 seconds and settled to idle. I did press the button as told. Sunday and Monday mornings, the truck started and fluttered but quickly recovered. I called the tech and provided the times so he could look it up on the live stream data logger. I was told to keep logging and they would contact me when they have the information. I was also told that 5 other customers have reported the same issue to this dealer so this could be bigger than first thought. I don't mind being the guinea pig or lab rat if this will help others.

Received a call from the service manager last week who told me GM Technical Assistance Centre was sending a Field Representative here to look into the issue with my truck. He then called me back a few hours later and said that they want to install a live link black box that will stream ECM diagnostic information over the cellular network. They have shipped the box here and in the meantime, i took my truck to the dealer to have the wiring connection installed so they can connect the box quickly once it arrives at the dealers service center this week.

My truck went to the dealership on Tuesday and GM gave me a rental to drive for the week while the tech took my truck home. It started normal the first few days but acted up Friday morning when he started it. Instead of revving to 3500RPM, the engine started then fluttered and stalled. He managed to record the event through the OBD Live Capture diagnostic reader and they now have something to work with. They called me to pick up my truck and the service manager told me that GM TAC is now looking into the cause and they have made it a priority. He also told me that another customer reported the same issue with their truck so I'm not the only one. I will let everyone know what the outcome is once they figure it out.

No it did not. It seemed to start normal for a few days after but it is still randomly starting and revving to 3500RPM. Service manager is talking to GM and they are going to give me a rental and take my truck until they figure out the issue.

The dealer called me today and said to bring it in tomorrow and they are going to install a new ECM. Hopefully this works.

So it went to the dealer a second time and they flashed a new BSCM calibration and it started fine until yesterday and it did its random start and redline. Tonight it fired and stalled then the starter cranked for 7 more seconds and it fired and redlined and held until i kicked the throttle pedal. It's going back to the dealer for a third time and they will keep it until they figure out the problem. 2019 AT4 Cold Start High RPM after long crank.mov

The Start/Stop button will shut the engine down. One time when the RPM took off to park redline (3500RPM), I just hit the start/stop button and it shut down immediately. I waited a few seconds and hit the start button and the engine started normally.

It did a slight flare on the post from Sunday but on Monday, it went to 3500RPM for almost 8 seconds. Tuesday it started normal and Wednesday (tonight) it sputtered on start up and only slightly flared up. Every time this happens, it has been sitting outside for 8-10 hours after finishing work in temperatures just below freezing. It never does it in the morning at home parked in my heated garage. Here is Monday's start up. I have my foot on the brake the entire time and lift it at the end. It going back to the dealership tomorrow.

I went to work today and after 10 hours of sitting outside in 20F cold, it started and fluttered and flared up to about 2000 RPM for 2 seconds then ack to idle and bounced up and down a bit. I never took my foot off the brake and did not touch the throttle. Video is noisy at the end as an aircraft was flying over on approach to the airport and I shut the drivers door. Guess the BSCM update didn't do much.

Here is the dealership technicians report: Nov 25 - Scan, no ECM codes stored and no bulletins apply. Codes U0140, U0131, U0151, U0102 and U0146 are set history in the BSCM which is related to bulletin 20-NA-155. A new BSCM cal is available to correct condition. Called TAC, no help. Removed the induction pipe at the throttle body, no sign of moisture or anything that would affect the throttle blade. The accelerator pedal is free of obstacles and does not appear to have anything that could hold it down. Parked truck outside over night. Next morning, Nov 26 - install the scan tool, monitor the induction data list and start. The engine RM flared up to 1850 then quickly down o a normal cold idle. The impression I got was an engine start with an incorrect idle learn. Found the idle compensation at 67% which seems high for a vehicle with 12K mileage. Inspect throttle body, completely clean. Correction: No repair possible today and no problem was found. I did install the latest BSCM cal, prog code 28YN51521209 for customer satisfaction and just in case it's related. Wipe down throttle body and perform an idle compensation relearn. Run and clear codes. The engine started without the flair this time. Customer to retry. I will give it some time and see if it happens again and post if it happens again....or not.

I showed the video to the mechanic at the dealership, its going in today.

Tonight I decided to start video recording when I left work. I was able to capture the event. I pressed the brake and start button and the engine sputtered then went straight to 3500 RPM (Park Redline) and stayed there for 10 seconds then went to idle. Check it out. Anyone hear about this happening to anyone else or have a possible cause? I now have something to show the service manager at the dealership. 2019 AT4 Cold Start High RPM.mov

The truck started normally for the last 10 nights and the issue happened again last night. The engine went straight to the regulated full RPM when in park and held until i shut the truck off after about 3 seconds. I restarted the truck and it started normally. I thought it could have been a fuel issue but have since filled up at other locations. Dealer hasn't heard of this issue, guess i will have to find an OBD2 scanner with live data capture and figure it out myself.

I know the RPM's are regulated in Park and could not tell exactly how high it revved because the speedometer and tachometer needles were doing their start up reset. It hasn't done it since and I'm recording every time i cold start it. I know if i bring it to the dealer, they will want to keep it overnight outside so they can cold start it in the morning. Now it is starting and almost stalling

I have the factory cold air intake. The dealer had to re-flash the ECM as a dealer installed option.

For the last week in outdoor temperatures below freezing, my 2019 AT4 6.2L has occasionally revved to redline on cold start after pushing the start button with my foot on the brake. This has happened 3 times in the last 4 days. I consistently use premium fuel only from the same gas station and cannot figure out why this is happening. Before i bring it to the dealer, who will want to keep it overnight, I was just wondering if anyone else has experienced this?

My 2019 AT4 build date 6/19 Fuyao E2 has been parked in my garage since new but after reading this post, I checked it in July and found it to be leaking. I've been driving around with a towel in the back window since then waiting for the dealer to get more experienced with the repair. I finally went to the dealer on a rainy day last week and the service advisor saw the leak on both sides and started to write it up. I questioned the repair and the service manager was consulted and he referred me to their body shop. I made an appointment with the body shop manager who stated they have done one repair to date but had to order the updated spoiler mount nuts. He called me back a while later to postpone the repair as there is no supply for the replacement nuts Canada wide. He said it could be weeks or months before they can get them from GM. Very disappointing.

I did another mileage check, this time I ran Regular 87 octane and the 64 miles from camp to home on the highway at just over the 55 MPH speed limit with the cruise control set at 57MPH and got 29MPG. My best mileage posted a few pages back was 28MPG and I have concluded that there is no noticeable difference between running 91 octane over 87 octane when driving economically. I did notice after the fuel mileage check when i strapped on my lead filled shoe, that the motor slightly knocked when pushed hard and the power was not the same. Back to premium fuel.

Did another mileage check returning home from camp. Last time got 28.4MPG with a tailwind at 55MPH. This weekend had a very slight head/crosswind and got 25MPG at 60MPH I have the CAI and Cat Back exhaust running 3.23 gears and 91 octane and 50PSI in my Duratrac tires.