Lately on cool mornings when I start the truck I have been experiencing some strange things. After starting I noticed on the gauge cluster brake light comes on, the indicator under the Park position is not lit and stays off no matter the position. Shifting into any position is not smooth but rather rough. If I attempt to drive the transmission will not shift to a higher gear and it seems to be stuck in either first or second. (High rpm and slow speed). After the truck warms up or if I start it later in the morning or afternoon it is fine. Any ideas
Strange symptoms
- Thread starter Jimmary22
- Start date
First check is to see what the fluid level is. The fact that the underline under the P indicator often says that the TCM or wiring has a problem.. Scan for aocdes with a tool that will read TCM codes. Not all readers will do that.
Thanks, I did check the brake fluid level and it is fine. I’m not sure if the scanner I have will scan for transmission codes.
I will check the transmission fluid level but as far as the temperature goes, these symptoms are at initial start on a cool morning before anything has a chance to warm up. Once it does the symptoms go away. Was wondering about moisture intrusion somewhere since it is located in north central Florida and the humidity is high even on cool mornings.
Transmission fluid is fine. Later in the day and symptoms are gone.
Used a scan tool and U0101 came up. (Lost communication with TCM) which makes sense except these symptoms only occur when it’s cold. I have hung a light close to the TCM and the ECM and after about a half hour everything is fine.
Almost brand new.
I read a GM bulletin that this could be caused by a corroded G102 ground. Ayone have any idea where this is located? 2008 3500HD LMM.
Should be lower left front of engine. Bottom of block.
A little more info for future needs
It’s in limp mode, you need a scanner to see what’s going on.
Yeah, been there done that.
Yep did that. U0101 comes up. The symptoms are only present on cool/ cold mornings.
Try grounding the tcm case externally, might have a bad tcm grounding. Lmm is known for it.
Tried that this morning, same results. Whatever it is, it is ambient temperature related. This morning outside temperature was 50 degrees. By this afternoon when the temperature rises the symptoms will be gone.
Pull the tcm and leave it inside the house over night, then plug it in the next morning and see what it does.
Probably needs a tcm
Probably needs a tcm
Good idea! I’ll give it a try.
Did this last night. Seems that is the issue. Now to try to find another preprogrammed TCM. GM discontinued the module as of March 2025.