GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hello. Is your Denali a 2 or***** and what engine is in it? I will see if I can get the information your looking for.
Ok. 1500, or 2500?
the shifting problem is most likely the result of low fluid. The temperature sending unit is located higher up in the transmission, so if the fluid was low enough, there wouldn't be enough fluid surrounding the sending unit to give an accurate reading. I have attached a picture with it's location. Item 34.
sorry that picture wasn't very good. here's a better one
Hopefully there wasn't any internal damage done. Does it eventually shift through all the gears, but just takes a while before shifting? Are you able to get a scan tool and check for transmission codes? I am reasonably certain that there are codes and they would help us greatly if you can get them..
Ok. It sounds like what you have is delayed shifts. It would be great to have the codes, but you may need your valve body reconditioned. This was a fairly common problem with your Denali and GM did provide instructions for reconditioning these valve bodies. There is also a TSB for it
You would get the codes from the OBDII port but your scan tool would need to be capable of reading transmission codes. I will attach a copy of the TSB with the information that covers among other things, a delayed shift condition.
It's the same transmission either way, but isn't your denali a 1500? (half ton)
It must be a 2500. The 1500 with the 6.0 was only availabe in XL. Anyway, thats not important. When you say delayed start, do you mean you give it the gas when it's cold and the motor just revs?
You wouldn't necessarily get all those codes listen in the TSB for a delayed shift issue. You could have some of those codes or symptoms or a combination of them.
In most cases a power train code will illuminate the light. Not always but usually. Regardless of whether or not there are stored codes, we do know that you have a transmission problem as delayed shifting is not normal. Delayed shifting is usually caused by sticking valves in the valve body, and it so happens that your transmission's valve body was prone to problems to the point that a TSB was issued for it. Even though your not finding any codes, I would perform that TSB.
If the computer doesn't recognize the issue, a code won't be stored. We see vehicles every so often that have a clear problem, misfires, etc.. and no CEL (check engine light). It just makes it a little more difficult to find the problem when that happens..
Woah, that's a bit of a twist.. Based on that last reply, I would be pretty confident that there is internal transmission damage. This no longer sounds like a simple delayed shift condition that does shift through all the gears.
skipping over second is exactly what would happen too if your 2-4 band broke
The 2-4 brake band is roughly a 10 hour job. The transmission must be removed to replace it. The 2-4 band is removed toward the beginning of the disassembly process, but it's a good idea to replace the clutches either way. He would have to remove the pan to see the 2/4 brake band to make a determination as to the extent of the damage, as he has said.
OH, I'm sorry I didn't answer your first question... The 2-4 brake band doesn't define a transmission overhaul. There's a lot more to an overhaul than that band. Much more dissassembly and reassembly and many more parts. Overhaul is a 15 hour job. ( including removal and installation of the transmission)
was it a broken 2-4 band?