2017 Tahoe harsh shifting and no cruise control
This Tahoe has a very intermittent concern. whether or not the symptoms are related, I don't know yet.
Customer states SES light came on and then went off. history codes found are posted above - cold start misfire. Misfire counter is highest on cylinders 3 and 4. Could not replicate issue, gave back to the customer.
The SES light never did come back on, but he brings it back in with an issue he says he's been having for a while. I take it for a drive with him and when slowing down, the downshifts are very harsh. The cruise control is also not working. I didn't have my scan tool with me on this drive, so when we get back to the shop, we chat a little bit, he agrees to leave it with me for a while. So now I grab the scan tool, go back out and drive it while monitoring data….. and it drives perfect now. I call him back and he says that after turning it off, it will “reset” and be ok for a few drive cycles and then it will act up again.
Now, to me, It feels like the transmission was in some sort of default and commanding higher line pressure, and the fault was also preventing the cruise from engaging as well. A full module scan did not reveal any faults beyond the history PCM codes. I did not find any TSB's related to this issue.
I am not as familiar with these newer GDI 5.3 engines, will the misfire codes cause a default “limp” mode that turns off the cruise control or cause the harsh shifting? I doubt this because he says the shifting and cruise concern will be present without the SES light being on.
If I can get the truck to act up again, any suggestions on what to look for on the scan tool? I don't want to chase my tail with the misfire codes if that is a totally separate issue from the trans.
Make sure the truck is in somehow being in advertently sent to “tow/haul” mode. That program will alter shift timing and feel
any modern GM (5-7 years young) and a harsh shift, we flash. or at least check for a flash/reflash.
There are multiple TSB's on the P050D. It relates to the injectors not flowing enough on cold start causing misfires. How many miles are on the car?? The 6L80 is garbage and usually needs a rebuild from about 50-100k. However not telling you the trans needs rebuilt. Just throwing that out there. Anyway you say the cruise is also inop. I would check the brake switch for maybe showing partially…
Hi change fuel injectors thatthe most common issue in this models
So I never was able to replicate the issue. I gave the truck back to the customer for two weeks, and he didn't have any symptoms. After talking with him, he authorized a transmission service and a reflash to the most current software. He brought it back in and I completed those repairs.