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New 2020 Sierra 1500 AT4 - Stuck in Park and Warning/Error Codes


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Less than 200 miles and the new AT4 is going in the shop...
 
Got in the truck yesterday, started it up, put in reverse and it would not move. It seemed as if the electronic e-brake was on, but the PARK light was not lit. Put it in park and hit the e-brake button, then the PARK light came on and started flashing and I got a message stating "Service Parking Brake", wonderful.
 
Turned car off, started back up, no more warning message and I was able to turn off the e-brake and reverse out of garage. Shortly there after I received two Onstar notifications, "issue with the StabiliTrak® stability control system" and "issue with the Antilock Braking System in your 2020 GMC Sierra has been detected".
 
The truck seems to drive okay, however I did notice some sort of clunking noise occasionally towards the back end, not sure if that's normal. Frustrating as I have barely even driven the damn thing since the dealer dropped it off new. It's going in for service this coming week. These issues seem somewhat similar to the past recall in the 2019s, although my vehicle says no recalls.
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That really sucks man. I had a check engine light  on my 2020 AT4 485 miles!! this morning when I went to work, but it was gone after work? I hope it was nothing, but makes me mad when you know they are new.

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On 5/16/2020 at 6:23 AM, Commander769 said:
Less than 200 miles and the new AT4 is going in the shop...
 
Got in the truck yesterday, started it up, put in reverse and it would not move. It seemed as if the electronic e-brake was on, but the PARK light was not lit. Put it in park and hit the e-brake button, then the PARK light came on and started flashing and I got a message stating "Service Parking Brake", wonderful.
 
Turned car off, started back up, no more warning message and I was able to turn off the e-brake and reverse out of garage. Shortly there after I received two Onstar notifications, "issue with the StabiliTrak® stability control system" and "issue with the Antilock Braking System in your 2020 GMC Sierra has been detected".
 
The truck seems to drive okay, however I did notice some sort of clunking noise occasionally towards the back end, not sure if that's normal. Frustrating as I have barely even driven the damn thing since the dealer dropped it off new. It's going in for service this coming week. These issues seem somewhat similar to the past recall in the 2019s, although my vehicle says no recalls.

I purchased 2020 AT4 6.2L 14 days ago - I drove it for 6 days before going back into the shop.  I didn't think anything about it, but after reading your post - I realized I had the same issue.  It would go into Reverse/Drive, but showed the P Brake was on, even though I hadn't put it on.  It's only happened once.  

 

My issue is - after the truck sat for a full day with the keyfob in the truck, I went to go start it and it wouldn't start.  The dash came on and said "Keyfob left in vehicle" and when I went to start....NOTHING.  No power, wouldn't even turn over.  I stepped outside with the FOB thinking I could remote start the truck and, nothing.  Had to connect jumper cables, to get it to start.  After it started, check engine light came on and it reset everything in the truck, put it into "DEMO MODE".  I've since dropped it off at the dealer, and it's been there a week......they said the code was a transmission code.  Super frustrated.....

 

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I'm curious if this is related to a low battery situation. I have a 2020 6.2 Tboss and I ran the battery down to the battery saver warning. When I started the truck up and drove it next I had several diagnostic issues including service the airbags and a few other codes. I threw a battery tender on it and charged it back up over that night and every code went away. I understand you aren't having these issues but I wonder if a low battery starts making these trucks act funny. I know others have had issues with the battery and I believe a few were throwing codes as well. Regardless I hope you get it fixed soon, I was just adding this as food for thought. 

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Dealer reset the codes and ran diagnostics, everything checked out fine, they said it was most likely a "glitch". Not sure how comfortable I feel with that diagnosis, but until it happens again, I guess I have to accept it...

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  • 1 month later...

Don't "accept it" if it happens again.

Have the dealer re-program the computer's software.

This fixed a friends Silverado 8 speed with shuddering shifts and failure to go into Park.

Your column shift isn't a mechanical lever anymore.

It's a switch.

The computers in these trucks control more than they did 10 years ago.

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