There have been a number of 2020 trucks with trans issues. I'm pretty sure I've seen a few post about no communication but haven't found those again yet.

2020 2500HD Transmission issues

 

Truck is still at the Dealer. They have opened an TAC with GM, but GM is not responding evidently. Of course, the service manager is out sick today and was on vacation last Friday. At their mercy at this point, but getting frustrated.

 

A. I find it very hard to believe that TAC hasn’t responded yet.

B. If the dealer can’t communicate with the truck did anyone bother to check and see if the dlc pins are possibly blown out from the Bank’s equipment being plugged in or even the power fuse for the dlc being blown? I know you don’t know the answers to these questions but most likely if a dealer can’t solve a simple complete lack of comm with the scan tool, without contacting TAC, then I would find a new dealer personally.

 

I'm not sure at this point what they have checked. I also find it hard to believe that GM hasn't responded. Not sure if the pins or fuse would be blown. The iDash was showing all the data I am monitoring. As for another dealer, not sure if they would be any better. I contacted GM, and they stated that they couldn't see a TAC. However, that was on the customer service side.

 

Customer service has access to TAC case data. If there was a TAC case started on it, they should have been able to see it.

If the iDash was staying powered up then most likely the fuse isn’t blown.

 

Got the truck back last night. My son picked it up as I was traveling. He called to say it wasn't right. I drove it this morning, and there is still a hunting either between 2-3 shift or 3-4 shift. CAlled the dealer, and he asked if I felt it was better. After paying for computer updates, which seems to not be covered under powertrain warranty, I told him I didn't pay for better, I payed for fixed. They are leaving the TAC open and seeing what GM says. Waiting again.

 

Why would you have to pay for updates? Was there a tsb for trans software update?

 

They said that the update would have come through on satalite, and since I had the derringer and iDash installed it couldn't come through. Therefore, I had to pay.

 

yikes. the derringer was still installed and the dealer noticed?

 

All you had to do is unplug the idash from the obd2. Did they give you documentation of what they did?

 

I had the complete iDash and Derringer unplugged prior to taking it in. I did that to make sure is wasn't a Banks Issue. I forgot the Pedal Commander, and they couldn't communicate with the trans computer because of that. they unplugged the commander and were able to re-program the computer.
The paperwork is in the truck and my son is driving it. I'll get it when he gets home.
Just got off the phone with the service manager. He understands the tuner aspect, and wants me to drive it to see if it relearns and go from there. I agreed, as I need the truck and don't have enough time to get it back to them. plus, they have no idea what they are going to do next anyway.

 

Drove the truck over the weekend. put a little over 300 mile on it. told the Service Manager i was going to plug in the iDash and set the gauge to show the gear that it is in. This also shows the torque converter lockup. So what I found, is that the jecking is going on when the torque converter is unlocked.

Taking the truck back to them today to see what they say.

 

So I got my truck back this morning. The Dealer had to replace the Trans computer based on GMs advice and the data that was supplied to them. I figured this as I stated above, the locking of the torque converter was causing the issues.

Funny though, the computer isn't covered under power train warranty. The dealer did go to bat for me and got it covered somehow. They also removed the S&B MAP spacer, as GM first told them to remap this. So, I am not sure what I want to do about that.I'm going to drive it a little before I reinstall the Derringer and the Pedal Monster. I know neither of these caused the issue, but they were very leary in the fact that they were on there causing them not to be able to communicate with the systems.

I'll see how it goes for a few days and make a decision.

 

You're very lucky that the dealer got the work covered. They must not have told corporate about the tuner. If anything happens like that again, completely remove all the gadgets not just unplug them.
When you're installing/uninstalling the Banks stuff, are you disconnecting both batteries?

 

You are correct, I will need to remove them. They have not been concerned in the past, but were this time. The pedal Monster seemed to keep them from linking with the system. Once unplugged, they were able to do the first reprogram.

The dealer didn't tell corporate about the Derringer, but told me if what they did, didn't fix it, I would have to remove completely everything.
When I disconnected the Banks, I did not disconnect the batteries, I am not sure why I didn't other than being in a hurry trying to move.

 

Fair enough, lessons learned. I have mentioned this in several other threads, but the computer in our trucks is never truly "off" even with the ignition off. In fact, it's even "on" sometimes with ignition off. If you disconnect harnesses while it's on, you can cause more codes.
Well, you got yourself a very nice dealer there. Other people haven't been as lucky as you. Glad to hear your truck is fixed.