2023 1500 AT4. CEL Code P20EE. LZ0 Diesel

Lawdog800 · Dec 25, 2022

First ever GMC truck I’ve purchased. Noticed a couple days ago the Check Engine Light was on. Happened to be a GMC dealer next door to where I was. The scanned and said it was code P20EE.

P20EE Code: SCR NOx Catalyst Efficiency Below Threshold (Bank 1)

That dealer did not have a Diesel tech working to ask so I left with truck. Pretty bummed with 920 miles. Other than that and the shifter trying to figure out trick to get into reverse without going back into neutral…… it’s a great truck. Miss my Cummins Ram. But not the mileage. 24.6 mpg out of second tank

slythetove · Dec 25, 2022

To get into reverse just hold the side button and press the shift lever forward. Mine goes right into reverse no need to stop in N

Rle312 · Dec 25, 2022

slythetove said:
To get into reverse just hold the side button and press the shift lever forward. Mine goes right into reverse no need to stop in N

You don't even need to hold the button, just press, release and push the shifer into R.

Lawdog800 · Dec 26, 2022

Rle312 said:
You don't even need to hold the button, just press, release and push the shifer into R.

Seems to pop back into neutral when I do that

Lawdog800 · Dec 26, 2022

Update: CEL went off. Truck now remote starts which it did not do with CEL on. I also got a DEF advisory now saying 250 miles to empty. I noticed the outside temp warmed up so I’m wondering if the DEF froze Causing the issue?

casshed · Jan 3, 2023

Did your CEL stay off? I got a 2023 Diesel AT4 as well and had the light come on twice now. Both for check emissions, first time the dealer just cleared it. Still have the light now and can’t get the dealer to look at it until next week. Started at 2800 miles and again at 3000…. I did get low on DEF when it started but filled it back up

Lawdog800 · Jan 3, 2023

casshed said:
Did your CEL stay off? I got a 2023 Diesel AT4 as well and had the light come on twice now. Both for check emissions, first time the dealer just cleared it. Still have the light now and can’t get the dealer to look at it until next week. Started at 2800 miles and again at 3000…. I did get low on DEF when it started but filled it back up

So far mine is still off. Temps outside have really warmed up however from zero to 5*f up to 20's-40's..