Intermittent Check Engine Light

[Beer Belly]

My Nephew has a 2021 Denali he bought used from a GM dealership I have an extremely good rapport with. He had an issue with his truck where the dash lit up like a Christmas tree and had a rough idle. I called those I know in the dealership service department and alerted them that "My Nephew is bringing in his truck with what sounds like the infamous Lifter issue". He brought it in and they first found two faulty Injectors, and still not running quite right, then went for the Lifters. I'm not happy with them going for the Injectors first (which are out of warranty), had a talk with them and they gave him very deep discount. Anyhow, since getting the truck back, he has an intermittent check engine light, truck runs rough, then light goes out and truck is fine, never lasts for a long period of time. He brought it back to the dealership, they have had the truck twice now, put 100+ miles on it and say they cannot replicate, my Nephew drives off and within 20 miles, experiences to problem. I've suggested they check for bad grounds, not sure what they have checked, I just feel they are ignoring the issue. I told my Nephew keep driving till you get a steady light or it blows up....can't fix it if it's not broke. Any ideas WTF is going on ?......does GM have a diagnostic tool that they could hook up and takes a picture of sensor readings 30 seconds before a CEL and during the CEL, to give the tech an idea of what is failing ?

[Transient]

9 hours ago, Beer Belly said:

My Nephew has a 2021 Denali he bought used from a GM dealership I have an extremely good rapport with. He had an issue with his truck where the dash lit up like a Christmas tree and had a rough idle. I called those I know in the dealership service department and alerted them that "My Nephew is bringing in his truck with what sounds like the infamous Lifter issue". He brought it in and they first found two faulty Injectors, and still not running quite right, then went for the Lifters. I'm not happy with them going for the Injectors first (which are out of warranty), had a talk with them and they gave him very deep discount. Anyhow, since getting the truck back, he has an intermittent check engine light, truck runs rough, then light goes out and truck is fine, never lasts for a long period of time. He brought it back to the dealership, they have had the truck twice now, put 100+ miles on it and say they cannot replicate, my Nephew drives off and within 20 miles, experiences to problem. I've suggested they check for bad grounds, not sure what they have checked, I just feel they are ignoring the issue. I told my Nephew keep driving till you get a steady light or it blows up....can't fix it if it's not broke. Any ideas WTF is going on ?......does GM have a diagnostic tool that they could hook up and takes a picture of sensor readings 30 seconds before a CEL and during the CEL, to give the tech an idea of what is failing ?

When the CEL is on or flashing your nephew could reach up and press the OnStar button.  They can run a diagnostic right then and there and then email him the info so he can provide to the dealer.  This does require an OnStar subscription.  Otherwise, he could spend $40 and get a cheap OBD2 scan tool.  The moment the CEL is in or flashing he could do his own scan right on the spot. 

[Beer Belly]

14 hours ago, Transient said:

When the CEL is on or flashing your nephew could reach up and press the OnStar button.  They can run a diagnostic right then and there and then email him the info so he can provide to the dealer.  This does require an OnStar subscription.  Otherwise, he could spend $40 and get a cheap OBD2 scan tool.  The moment the CEL is in or flashing he could do his own scan right on the spot. 

I will let him know to give that a try, not sure the CEL stays on long enough, he sez it only last a minute or so. Thanks

[Bikerjon]

On 3/27/2025 at 6:28 AM, Beer Belly said:

My Nephew has a 2021 Denali he bought used from a GM dealership I have an extremely good rapport with. He had an issue with his truck where the dash lit up like a Christmas tree and had a rough idle. I called those I know in the dealership service department and alerted them that "My Nephew is bringing in his truck with what sounds like the infamous Lifter issue". He brought it in and they first found two faulty Injectors, and still not running quite right, then went for the Lifters. I'm not happy with them going for the Injectors first (which are out of warranty), had a talk with them and they gave him very deep discount. Anyhow, since getting the truck back, he has an intermittent check engine light, truck runs rough, then light goes out and truck is fine, never lasts for a long period of time. He brought it back to the dealership, they have had the truck twice now, put 100+ miles on it and say they cannot replicate, my Nephew drives off and within 20 miles, experiences to problem. I've suggested they check for bad grounds, not sure what they have checked, I just feel they are ignoring the issue. I told my Nephew keep driving till you get a steady light or it blows up....can't fix it if it's not broke. Any ideas WTF is going on ?......does GM have a diagnostic tool that they could hook up and takes a picture of sensor readings 30 seconds before a CEL and during the CEL, to give the tech an idea of what is failing ?

Grounds cause a lot of problems on these trucks. There was a bulletin about improper grounding at the engine fuse block a few years ago. Unfortunately grounds/electrical problems are extremely difficult to trouble shoot. Especially intermittent faults.

[GMCustomerService]

On 3/27/2025 at 6:28 AM, Beer Belly said:

My Nephew has a 2021 Denali he bought used from a GM dealership I have an extremely good rapport with. He had an issue with his truck where the dash lit up like a Christmas tree and had a rough idle. I called those I know in the dealership service department and alerted them that "My Nephew is bringing in his truck with what sounds like the infamous Lifter issue". He brought it in and they first found two faulty Injectors, and still not running quite right, then went for the Lifters. I'm not happy with them going for the Injectors first (which are out of warranty), had a talk with them and they gave him very deep discount. Anyhow, since getting the truck back, he has an intermittent check engine light, truck runs rough, then light goes out and truck is fine, never lasts for a long period of time. He brought it back to the dealership, they have had the truck twice now, put 100+ miles on it and say they cannot replicate, my Nephew drives off and within 20 miles, experiences to problem. I've suggested they check for bad grounds, not sure what they have checked, I just feel they are ignoring the issue. I told my Nephew keep driving till you get a steady light or it blows up....can't fix it if it's not broke. Any ideas WTF is going on ?......does GM have a diagnostic tool that they could hook up and takes a picture of sensor readings 30 seconds before a CEL and during the CEL, to give the tech an idea of what is failing ?

Although your dealership is in the best position to assist, we would like the opportunity to work alongside them to address the concerns your nephew is facing. So that we can help, please have him reach out to our team at [email protected]. We will be on the lookout for that message. By sending us a message, you consent to the information you provide being monitored and recorded by GM or those acting on GM’s behalf, subject to the GM Privacy Statement: https://www.gm.com/privacy-statement.