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Discussion Starter · #1 ·
I have a new 2021 AT4 Duramax. I filled the DEF fluid for the first time (it has about 2300 miles on it) When I started it to leave the station, the check engine light was on. I drove it home (6 miles) and it didn't go off. Could this be related to filling the DEF tank. I guess it's possible I over filled it. Any ideas? Thanks.
 

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2017 GMC Denali 2500HD, 3.5" Rough Country Lift, 305/55R20 Cooper Rugged Trek, Paragon Bed Cover
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Overfilling won't throw a check engine light; it will just spill out the filler neck.

It's hard telling what could be the issue without knowing what code the truck is throwing. If you don't have a code reader or monitor ( we ALL recommend getting one if you own a diesel; Banks iDash or Edge CTS are the favorites), you can go to one of the chain automotive stores like Advanced Auto, AutoZone, or O'Reilly and they can read the code for you. At that point we can help you potentially figure out the issue. You'll also be more informed when/if you have to take it to the dealership for repair.

The other option is you just go to the dealer and have them fix it since you're well within warranty having only 2300 miles on the truck.
 

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Discussion Starter · #4 ·
Overfilling won't throw a check engine light; it will just spill out the filler neck.

It's hard telling what could be the issue without knowing what code the truck is throwing. If you don't have a code reader or monitor ( we ALL recommend getting one if you own a diesel; Banks iDash or Edge CTS are the favorites), you can go to one of the chain automotive stores like Advanced Auto, AutoZone, or O'Reilly and they can read the code for you. At that point we can help you potentially figure out the issue. You'll also be more informed when/if you have to take it to the dealership for repair.

The other option is you just go to the dealer and have them fix it since you're well within warranty having only 2300 miles on the truck.
Thanks.
Also, OnStar will send you a maintenance report that will include the thrown code.
I didn't know that. Thanks.
 

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Just a FYI - you posted this in the LBZ / LLY Forum.
 
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