Exhaust Brake concerns

DBaker · April 14, 2025

I have a 2025 GMC 2500 Sierra with Duramax. Its not in the shop for the 4th time for the same issue, but this time they had a recording computer hooked to it to see if they could diagnose it. So far they have been unable to figure out the cause of the issue which is it goes into limp mode, traction control light comes on, service light on, reduced accleration message. After shutting it off, giving a little bit and restarting, everything but the check engine light goes away. AFter it sits a day, that does away as well. Its giving P060C code. Softwares have been flashed multiple times, new gateway module put in it, and GMC regional tech has been there over 15 hours working on it and found nothing.

So when i took it in Saturday morning, the service manager saw that i had made note that i had the exhaust brake on. He immediately said this may be whats causing it. He said you can't use that unless on the highway and pulling a trailer of some sort, and that the owners manual states that. I have looked up the exhaust brake in owners manual and there is nothing saying you can't use it in town or without a trailer or anything to that affect. This issue has happened to me 5 times now since beginning of the year, twice with exhaust brake on, 3 times without it on so that alone tells me it is not the issue.

Has anybody else experienced this type of issue with exhaust brake? Been told you can't use it in town or without trailer? Given any conditions you cannot use the exhaust brake for? I feel like this is a copout basically because they don't know what else to say. They have a tech case open with GM and i have case open with GM also for possible buy back or something else if issue gets fixed. Anybody have any thoughts or experienced anything similar to this?

64BAwagon · April 14, 2025

I think your analysis of the techs comments are accurate. Some people feel the need to say something even if they have nothing to say. Any claims made and not substantiated by a document or the manual should be dismissed. I would make note of this event and start keeping a log of any interactions going forward. Ask them to put everything in writing via an e-mail or text you can save. If it aint written down it didnt happen. This will help in the end if a resolution isnt found.

newdude · April 14, 2025

1 hour ago, DBaker said:

I have a 2025 GMC 2500 Sierra with Duramax. Its not in the shop for the 4th time for the same issue, but this time they had a recording computer hooked to it to see if they could diagnose it. So far they have been unable to figure out the cause of the issue which is it goes into limp mode, traction control light comes on, service light on, reduced accleration message. After shutting it off, giving a little bit and restarting, everything but the check engine light goes away. AFter it sits a day, that does away as well. Its giving P060C code. Softwares have been flashed multiple times, new gateway module put in it, and GMC regional tech has been there over 15 hours working on it and found nothing.

So when i took it in Saturday morning, the service manager saw that i had made note that i had the exhaust brake on. He immediately said this may be whats causing it. He said you can't use that unless on the highway and pulling a trailer of some sort, and that the owners manual states that. I have looked up the exhaust brake in owners manual and there is nothing saying you can't use it in town or without a trailer or anything to that affect. This issue has happened to me 5 times now since beginning of the year, twice with exhaust brake on, 3 times without it on so that alone tells me it is not the issue.

Has anybody else experienced this type of issue with exhaust brake? Been told you can't use it in town or without trailer? Given any conditions you cannot use the exhaust brake for? I feel like this is a copout basically because they don't know what else to say. They have a tech case open with GM and i have case open with GM also for possible buy back or something else if issue gets fixed. Anybody have any thoughts or experienced anything similar to this?

That's a line of horse. Exhaust brake can be used any time you want to and it would not cause that code to set.

DTC P060C is Control Module Main Processor Performance. It can set for the ECM or the TCM, and possibly other modules. Its a computer processor issue that could be from an intermittent faulty ECM or TCM or wiring to those.

The GM regional tech should try an ECM or TCM (whichever is setting that code) if they have not already done so (instead of just flashing things) and see if anything changes.

Any chance you can ask them for a copy of the SAVI printout with DTCs and post a picture of it here?

DBaker · April 15, 2025

I can ask for it next time i go there. I'm not familiar with that but i can ask. There were originally going to replace ECM I believe, but the engineers said not to cause it wasn't problem. Apparently there are multiple trucks out there with this problem and no fix yet. Not sure why the engineers think its not the problem.

DBaker · June 4, 2025

Just to give an update, the issue with the exhaust brake appears to be torque converter related. AFter much aggravation and fighting with it, they found the issue happens during deceleration when it goes into 5th gear around 35-40 mph. The engine rpm and the input shaft on tranny rpm are not syncing, which is causing the truck to go into derating mode and codes to come up. They put a new torque converter into it and it seems to have fixed the issue at hand, however now it leaks tranny fluid from what appears to be the input shaft area of transmission. I'm done fighting with it. The truck is going back to GM for a buy back hopefully and i'll start over with another new one.