GJR1212

GM issued a revision to the ECU software in early October that seems to be fixing this problem for most folks. They apparently are not going to notify owners about the hew software and your dealer may not be aware of it either. Tell your dealer that there is a revision. You can find more info from earlier posts.

What I read says that GM released the version to correct long crank/no starts 10/1/21 and then revised it again 10/4/21. Sounds like you still have the not had the ECU program update that addresses this problem.

One bit of misinformation that my saleman had been told by the service department, is that the auto restart system does not cause wear on the engine starter. I think this bit of 'folklore' comes from the fact that hybrid cars use the big electic motor to restart the gas engine. If you notice when riding or driving a hybrid the starting of the gas engine is almost undetectable since it is so smooth a transition. Our truck use an old fashion starter to start. It and the flywheel gear, bendix and starter gear teeth all wear incrementally with each start.

My truck has three of those same relays in the underhood fuse box. One for start, one for the headlights, and one for running lights. If someone wants to see if it the relay, just rotate it with one of the ones doing light duty. It pretty easy to tell if your lights still work. My guess is your dealer didn't know what to change so they changed the cheapest part they could find. These relays sell for about $10 from GM OEM dealers. Dealers seem lost when it comes to troubleshooting this problem. I wish GM would explain what they changed in the ECU program. My guess is they are adding some time delays to give the ECU time to see all the inputs in what is likely a long list of parameters. Or, perhaps they are just giving the fuel pump and little extra time to spool up.

Googled that part number. It is a pretty genaric relay of the type used to isolate the higher current load circuit from the lower current control circuit. It is a $10.20 part. I can't see how it could be related to the parts shortage since almost any GM suppliers of electronics could make this part.

I've read most of the post on this and I do not recall anyone having a long crank, no start from the auto start/stop. The ones that do it most offend seem to get with the remote start as well as the dash button start. If your foot is touching the gas or the floor mat is laying on the gas, you will get long crank, no start as well.

I like my 3.0 GMC 4wd truck. It gets great fuel mileage in normal rural driving. It is averaging around 25 mpg. It also tows my RV better than my old 5.3 Silverado or my 5.4 Expedition. The 10 speed transmission is very smooth. I have had one long start episode. Unless you have to have a new SUV today, I would wait and get one next spring. GM will eventually fix this problem, but right now they seem to be selling their gas trucks as fast as they can build them. They do not seem to see the hiatus in 3.0 productions a serious problem- in my opinion. My guess is the number of truck really seriously impacted with these long starts is a modest number. Albeit, it is a big issues with those of us involved. Discounts and Incentives do not seem to be what you would expect at a model year end either which is perhaps another reason to wait and get a 2022.

I think GM, by now, knows exactly the cause or causes of long starts. IMHO, their problem is finding a solution that does not involve a major recall of thousands of trucks. As I have mentioned, it could be substandard chips in the ECU. Replacing 20k or so ECU means they sell 20k fewer trucks since chips are limiting production. Why did they stop sales of 3.0's? Perhaps the long crank problem is at least part of that decision. They also figure that their gas trucks will garner any lost 3,0 sales. I do like my truck and do not want to sell it back to GM, but I'm getting a little annoyed at the lack of progress from GM on a significant number of defective trucks. I do not want to keep a truck that a dealer has taken completely apart and fully support those who have enacted the lemon laws to get their money back.

I have wondered whether the fact that GM has been short processors if they have lowered their acceptance standards for ECU chips. A substandard chip would be slower than expected. Modern chips are really faster than we are at tripping switches. The designers probably assume this. Assuming you are correct that the ECU is loosing the relay race, it should be easy for GM to add logic to wait for all required automatic actions to complete before starting the cranking. Also, they should shorten the cranking to something like 4 seconds instead of 20 or 30 as it is now. About half the time I hit the button before remembering to step on the brake. So, I have been pretty much following you method. I've have had only one long start. Hope some other folks with frequent long starts will try your method and report if they still have long starts.

You should at least get the code read at an auto parts store, if you do have a code reader, before you head out on a long trip.

My 2021 had a CEL come on so I returned home and turn the truck off while I opened the gate. When I restarted it, I got my one and only, so far, long start. Once it quite grinding the starter, I attempted a restart. The engine started normally and the CEL was off. Took to the dealer ASAP and the dealer found no explanation for the long start but wanted to order a bunch of parts to address the CEL they found in the ECU memory for control of the radiator dampener. When I got home, I torque the fuse box which was quite loose to 53 inlbs. I did not take it back to the dealer since it has not throw another CEL. It also has not had another long start in about 1000 miles of driving. The four bolts of the fuse box hold the harness plug on the back side of the box to the corresponding connects to the fuses and relays. I do think some of the problems with intermittent elecrical problems relate to these bolts working loose. I believe mine were torqued from the factory because each of them had a white grease pencil check mark net to them. For some reason they work loose. I re=torqued mine a week or two later and they were again somewhat loose. Check yours after a few weeks and see if they have loosened.

Did they say what they did to correct the regen knocking?

Sorry, I misread your earlier comments. So far I am pleased with how the 3.0 runs and how well the 10 speed compliments the engine. I hope you are wrong about there being a fundamental flaw in the design. You may recall the fiasco in the mid 80's when GM tried to make a diesel v8 out of a gas v8. That was a flawed design for sure. My point was this engine seems very similar to the TDi design that runs a great number of euro cars and still a few here. I do think carbon build up could happen quickly when running excess fuel over a hot exhaust valve. Perhaps your truck has some problem with the regen fuel enrichment controls. I did see on one of these forum someone else complaining about knocking, I wonder if this is problem is common to the design or more something specific to a few offending trucks?.