Multiple error messages on new truck

[Ctsha]

Hi, I came across this forum trying to research a reoccurring issue I’m having and haven’t had any luck finding anything out there.

I bought a new 2021 Sierra 1500 AT4 3.0L about a month ago (March 2022). Supposedly it was held back due to the microchip shortage. When It was delivered to the dealership it had 8 miles on it. The dealership is in another city and they drove it to my house, arriving with just over 200 miles on it…
The next morning after getting it delivered, I ran some errands around town. After about 20-30 miles, it went into “reduced power mode” while driving. It would rotate through error messages saying “service ECS”, “service parking brake”, “service emissions system, see owners Manuel”. It also had check engine light on, parking brake light on, and I believe traction control light. I limped it into the dealer and they were able to see all of the error messages. They hooked it up to their computer and documented what codes it was showing (sorry I don’t know specifics). After having it back on their lift for a couple hours, they returned it to me saying they couldn’t replicate the problem and the codes have now cleared. The service advisor said he didn’t know what could have caused it and just said to drive it and hopefully it doesn’t happen again.. if it does, bring it back in.

The truck drove good for about 4 weeks after that. No issues. Today, while driving on the freeway, slow and go traffic, the exact same thing happened again. This time there was pretty significant vibration from the front of the vehicle. The maps on my screen when blank, then came back on with what looked like a zoomed out map of earth and froze there for a few minutes before going back to normal.. all of the same error messages were showing. I called the dealership and they suggested I drive it there if able to.. I took some photos and video of the messages, and was able to get it over to the dealership in “reduced power mode” going about 20 mph. Any speed over that and the vibration would increase significantly. The truck now has 1,039 miles on it.

I’ve had it for about a month and haven’t even made the first payment on it. I regularly take road trips about 200 miles each way and don’t want to have this happen on the highway far from town. I never got any answers the first time I brought it in. The dealership said it might take them a few days to get back to me this time around and put me in a rental..

Sorry for the long story, but has anyone experienced this or have any insight? Does this sound electrical, something to do with the microchip, or something else? I’m hoping I don’t get the truck back with no answers again.

Thanks in advance

 

[BoostN]

Welcome.. I'm pretty clueless on this one myself. Likely a bad ECM or something weird like that.. have your dealer check it out and let us know what they say!

 

[Mooseman]

For multiple systems failing like that, sounds like an electrical or ground issue. I know on older trucks, when the ignition switch fails, multiple systems will throw errors. Vibration is maybe misfires. If a pump is not working correctly and not fueling right, it could do that. Just guesses on my part.

Take it to the dealer. If they can't fix it, lemon law should kick in.

 

[gemarsh]

This would be worth trying.

 

[rbdjr]

I'm thinking , a ground like previously said, or a power interruption, Could be a rub through the condition and has to be that same conditions met to duplicate, wire harness rub and vibrate and could be spot size of a ball point pen tip, could be tough till it gets worse. Have some Patients, Could take some time to repair unless it happens more often, keep us informed on what is found.

 

[Bobho]

I had all the same on my 2021 1500 with 24k I bought new last year.I’m old and too busy so traded mine in between check engine lite episodes.there are dozens of these for sale with 8k to 20k miles in my mid size city.makes you wonder.first one in the life boat?

 

[Ctsha]

Thanks for the replys. It’s been at the dealership for 12 days at this point and I’ve been in a rental. The last time I talked to them they said they’re chasing wires but haven’t located the problem yet. I’ll let you guys know when I hear anything

 

[Bobho]

You must have massive patience.I admire that.those trucks are great until they are not

 

[NEVADADSL]

My next door neighbor has similar issues on his '21 Denali. They were traveling in Roseburg, OR, when dash lit up and went into limp mode at ~28K miles. Took it to local dealer and was told the wiring harness has 2 branches - 12V and a 5V. His issue turned out to be the wiring harness was routed too close to a heat source in the engine compartment and fried some wires. It was repaired and they were on the road in a couple of days (BTW, the Roseburg GMC was really great, according to my neighbor). Apparently there is a TSB on this problem. Fast forward to neighbor finishing trip and returning home here to No. NV. Dash lights up, limp mode again. Takes it to local dealer (Michael Hohl GMC in Carson City, and it has been there for 10 days now with zero updates from the dealer. They promise to call him and never do. He is beyond frustrated from the crappy service and false promises from this dealer. Still no resolution to his problem.
Once things get sorted out he will probably sell the truck. I will be getting the TSB from him as well so I can possibly be proactive and have it taken care of in my truck.

 

[gemarsh]

The TSB would be nice. I could take care of it myself, before damage happens.

 

[Ctsha]

Just stopping back in to give an update on my original post..

The dealership tried multiple fixes that didn’t resolve the issue and filed an inquiry with GM. They were instructed to replace the wiring harness. Just like the post above, the tech said it looked like there was possible heat damage to the wiring harness. It was in the dealership for about 26 days trying to figure it out and the entire harness was replaced.

First drive on the freeway once I got it back, the check engine light came on. I brought it back in and diagnostic test showed a code for the cadillic converter being bad.. the service manager told be it might of damaged it or a sensor when it misfired while in limp mode???? They ordered the new cadillic converter and I drove the truck in the mean time as they said it wouldn’t cause further damage. 2 weeks later the new cadillic converter came in and they replaced it in an afternoon.

I’ve put about 3k miles on it since then with no further issues. Hopefully everything is resolved