SEL light discussion (what's causing it?)

kmeleon · August 25, 2021

5 hours ago, Rhino83 said:

Talking about ECM updates and the 10 speeds...I too have had the CEL but no performance issues that I can tell. However, I have taken my truck in four times now but the first two were computer hookups and the last two were service appointments that are related to this very issue. The first service appointment, they updated the software in the ECM. Drove it for about a week and a half and CEL came back on. After two days, light went off and I got an appointment about a week later. This time they discussed replacing the ECM since the ECM already had the updated software. Was told when I picked it up that the ECM software was not designed for the 5.3s with 10 speeds and that GM was working on an updated software. Tech even showed me the bulletin. Just some food for thought I guess.

Thanks for your input. When your SEL goes off, is there any similarity to how you're driving? Light throttle? Certain speed? Early in your drive? After coming to a stop?

Just trying to see how it happens for others.

Thanks

Mitchy21 · August 26, 2021

I feel like I'm going crazy when I drive mine. 2021 5.3 Trail Boss, build date 7/21, 1,700 miles, bought just over a month ago. I swear I feel constant misfires when holding speed on the highway or going up a long slight grade. It's not pronounced at all, I don't think a passenger would even notice, almost just feels like tiny constant bumps in the road. Maybe all in my head from reading this forum too much? RPMs between 1100 and 1400. I drive the same roads every day, and I swear I didn't feel this for the first 1,500 miles. Not sure if it's misfires, or if the truck is going into 10th gear when it really shouldn't be and bogging down?

kmeleon · August 26, 2021

14 minutes ago, Mitchy21 said:

I feel like I'm going crazy when I drive mine. 2021 5.3 Trail Boss, build date 7/21, 1,700 miles, bought just over a month ago. I swear I feel constant misfires when holding speed on the highway or going up a long slight grade. It's not pronounced at all, I don't think a passenger would even notice, almost just feels like tiny constant bumps in the road. Maybe all in my head from reading this forum too much? RPMs between 1100 and 1400. I drive the same roads every day, and I swear I didn't feel this for the first 1,500 miles. Not sure if it's misfires, or if the truck is going into 10th gear when it really shouldn't be and bogging down?

Most likely it's dfm causing it, I've noticed it as well. Shift the truck to L9 for a drive and see if you notice it still. That will deactivate dfm.

Mitchy21 · August 26, 2021

21 minutes ago, kmeleon said:

Most likely it's dfm causing it, I've noticed it as well. Shift the truck to L9 for a drive and see if you notice it still. That will deactivate dfm.

Hmm...I assumed I didn't have DFM on mine due to chip shortage. I didn't get the auto start/stop. I'll have to check the sticker in the morning. Is there anyway to check that other than the sticker that you know of?

Mitchy21 · August 26, 2021

7 minutes ago, Mitchy21 said:

Hmm...I assumed I didn't have DFM on mine due to chip shortage. I didn't get the auto start/stop. I'll have to check the sticker in the morning. Is there anyway to check that other than the sticker that you know of?

Nevermind...just found an article that lists the models that kept the DFM. LT Trailboss is one of them. There's no way this is how the truck is supposed to drive. It's annoying the hell out of me. Almost like the cylinder management is over managing and activating/deactivating cylinders so frequently that the truck gets a slight stutter.

kmeleon · August 26, 2021

8 hours ago, Mitchy21 said:

Nevermind...just found an article that lists the models that kept the DFM. LT Trailboss is one of them. There's no way this is how the truck is supposed to drive. It's annoying the hell out of me. Almost like the cylinder management is over managing and activating/deactivating cylinders so frequently that the truck gets a slight stutter.

Yeah give L9 a shot and see what happens on your next drive on that stretch of road.

tootall4289 · August 30, 2021

On 8/20/2021 at 11:41 AM, kmeleon said:

Bringing this back to the top. Heard back from the investigator yesterday. Basically she has nothing to tell me yet, she spoke to the dealership and they claim that I'm bringing my truck back in for service but that's not true I don't have an appointment currently and no one has reached out to me. She does say GM is working on the issue if indeed my problem is the same as what they believe it to be and that she doesn't have an update on that or when that fix will be released. My response to her was how long am I supposed to drive this truck that flashes the SEL light every couple of days? I started mentioning lemon law with her and that may get me somewhere she's looking into an extended warranty on my truck to keep me happy. I'm not sure that's going to happen though. I told her I would reach out to the general manager at the dealership and put a good faith effort in with him but if nothing else comes from this I'm going to demand to buyback and ask for a new GMC or possibly go buy a Tundra.

I'm getting even better at setting the service engine light off. I can almost do it at will each day. So that will be helpful in eventually showing somebody the issue.

This sucks, I love my truck but I don't know how long I'll continue this game with them. I may go test drive a tundra this weekend.

Any update from GM? Mine is doing the same thing.

kmeleon · August 31, 2021

8 hours ago, tootall4289 said:

Any update from GM? Mine is doing the same thing.

They called me back today, she's working on a rental car for me for when the truck goes in. But the funny thing is, they don't know what is causing it so they don't really have a plan to repair. They're bringing a district general manager in on the repair so she tells me. I asked what are they going to do when the truck won't pass emissions testing in November when the car is due for inspection since I can make the light go off pretty frequently. She was kind of dumbfounded when I asked what gmc is going to do at that point. I told her that's pretty much the end of the road for me, at that point I figure I've given them about all the time I'm going to. I told her I'd expect a buyback at that point or ill lemon law it.

usmcav8or · September 21, 2021

To the OP, kmeleon, you are describing EXACTLY the behavior of my brand new 2021 1500 AT4 w/5.3, mine did the CEL light at 937 miles, and again today at 1300 miles, the first time it happened I pulled and cleared the P0300 code myself using a scanner, today it cleared itself when I shut the truck off and restarted it. This is my very first GM product and like you I also love everything about the truck, but holy cow what a POS system this DFM is, I don't have time in my life to go to the dealer so he can chase random P0300 codes, I am so pissed and disappointed in this truck, don't know why I gave GM a shot, my concerns about their poor quality were spot on, and now it's biting me, I wish I would have waited for the new Tundra Any updates you have on your case are appreciated, I intend to take mine to the dealer asap, although reading the forums it seems like I'll be wasting my time having them try to chase down a spurious code....

kmeleon · September 22, 2021

22 hours ago, usmcav8or said:

To the OP, kmeleon, you are describing EXACTLY the behavior of my brand new 2021 1500 AT4 w/5.3, mine did the CEL light at 937 miles, and again today at 1300 miles, the first time it happened I pulled and cleared the P0300 code myself using a scanner, today it cleared itself when I shut the truck off and restarted it. This is my very first GM product and like you I also love everything about the truck, but holy cow what a POS system this DFM is, I don't have time in my life to go to the dealer so he can chase random P0300 codes, I am so pissed and disappointed in this truck, don't know why I gave GM a shot, my concerns about their poor quality were spot on, and now it's biting me, I wish I would have waited for the new Tundra Any updates you have on your case are appreciated, I intend to take mine to the dealer asap, although reading the forums it seems like I'll be wasting my time having them try to chase down a spurious code....

It just so happens that I changed dealers and GM set up an appt with them for yesterday. They gave me a Buick encore to drive while they had my truck, which surprisingly they called about already today and told me it was done and ready to be picked up. This dealer finally did the program update (according to them one of their techs had the same problem on their truck, fixed it). So fingers crossed it works. I'll know by the end of the week because I can make the light flash just about everyday when I'm trying. I'll report back in a few days. Thanks for adding your input about your truck, sorry to hear you're having issues.

Edited September 22, 2021 by kmeleon

usmcav8or · September 28, 2021

So, full history so far on brand new 5.3L Sierra AT4: SEL at 900 miles, cleared code myself (P0300), SEL again at 1600 miles, took to dealer, they did service bulletin 21-NA-154, (update ECU and relearn on camshaft sensor), driving home tonight at 2200 miles, SEL is on again. Plan to contact dealer tomorrow, very upset, if this isn't fixed asap, I'll have to start looking into remedy under lemon laws Info from anybody else having this (or had this) as an ongoing issue is appreciated.

kmeleon · September 28, 2021

7 hours ago, usmcav8or said:

So, full history so far on brand new 5.3L Sierra AT4: SEL at 900 miles, cleared code myself (P0300), SEL again at 1600 miles, took to dealer, they did service bulletin 21-NA-154, (update ECU and relearn on camshaft sensor), driving home tonight at 2200 miles, SEL is on again. Plan to contact dealer tomorrow, very upset, if this isn't fixed asap, I'll have to start looking into remedy under lemon laws Info from anybody else having this (or had this) as an ongoing issue is appreciated.

Update: I've been driving the truck for five days since the TSB was done. Yesterday the light again flashed under the same circumstances. I called GM and called the dealer and set up another appointment for next week. We'll see what they try next. I really thought it was fixed after 4 days of no light

tootall4289 · September 28, 2021

53 minutes ago, kmeleon said:

Update: I've been driving the truck for five days since the TSB was done. Yesterday the light again flashed under the same circumstances. I called GM and called the dealer and set up another appointment for next week. We'll see what they try next. I really thought it was fixed after 4 days of no light

Mine is doing they same thing. They did the reprogram and it stayed off for two weeks and now it is flashing again. Interested to hear your update Kmeleon.

kmeleon · September 28, 2021

2 hours ago, tootall4289 said:

Mine is doing they same thing. They did the reprogram and it stayed off for two weeks and now it is flashing again. Interested to hear your update Kmeleon.

I'll report back after the appt in a week.

usmcav8or · September 28, 2021

I took mine to dealer this a.m., mechanic pulled code P0300 (again), couldn't find anything else wrong, he asked me to drive and monitor for a couple weeks and he'll keep the service ticket open. I'm willing to let the dealer give this an honest try, but bottom line is they don't know what's wrong with it, let alone how to fix it, and really it's a design flaw from the factory. It's very concerning how many 5.3's have had this problem, I found a similar thread on another site, seems there are a slew of Trail Boss owners reporting same situation. Lemon Law's vary by state, I've already looked at how it works in mine (MD), I would like to believe that this issue can be resolved because I really do love the truck otherwise, it rides great, quiet cabin, nice radio, the 5.3 is actually a really nice motor, the 10 speed tranny does a great job, literally have nothing but praise for the truck, but obviously this situation with the SEL is absolutely 100% unacceptable. It totally baffles me what thought process led GM to conclude that the AFM/DFM was worth the hit to reliability and their brand reputation, the customer aggravation, etc. All that to get a fleet increase of 1 mpg?! Tundra's get 14-15 mpg and people love them because they are a bulletproof rock-solid reliable powerplant. What customer would chose 1 mpg if it meant introducing the complexity of DFM, nobody would be dumb enough to do that (except a GM engineer).

I will certainly report back with updates, hope others will post their experiences as well.

It would be interesting to know manufacturing dates of the troublesome trucks?