So I popped for the HP tuners and the first thing I was going to do was adjust the tire/ gear ratio to bring up my cruise rpm (even though I am in the middle of GM's recommendations). Pretty disappointed to find the TCM is locked. Yes I understand I could send it to HPT, WTF! Anyone else running the 8L90 transmission have feedback on their cruise rpm's?
So truck has been sleeping all winter and took it out a couple of days ago. Drove fine until I gave it significant gas and it rev'd then not several times. Came home and has check engine light on PO700 which is a transmission code and P18C2 pending. Also am told shifter positions are PRNDM. Mine and at least 2 others have one more detent, PRNDM? Heard it could be PRNDML?
Have you called GM or talked with a GM performance dealer about it?
I chatted with a GM performance tech today. Says delete codes and see what happens. I asked about the extra shifter detent (2 of my buddies have same) and all I could get from him was don't use it.
So I removed the battery power and then powered backup. Problem remains. Works fine in drive but when I shift to manual the shifter indication does not change, still shows its in drive. It does go down a gear and stays there but cannot manually shift.
Have an appointment with a GM dealer. Called GM tech line again to ask for a answer on the extra shift detent, no answer yet. Also asked for warranty as I have just 600 miles on it but just over the 2 years. It is always tough building a vehicle under 2 years as you generally buy your drivetrain to fit first and then build the rest. My buddies that bought the same engine and trans packages about the same time I did do not have their projects completed yet. But they both have the extra shifter position that I have.
Last edited by vet57air; 05-18-2022 at 10:45 AM.
The Following User Says Thank You to vet57air For This Useful Post:
Had my appointment with a Pacific GM dealer today. They treated me very well. Spent a couple hours testing to checkout the P18C2 code which is "internal mode switch". Next step is taking the pan off so we have ordered a mode switch in case that ends up being the problem. Still have not heard back from GM on warranty or extra shift detent.
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