Mystery Button

[Johnny Ola]

What is the button used for that is located next to the fuel filler opening?

[WyoAT4]

DEF

[Johnny Ola]

DEF?  Could you please be a little more specific.  Thank  you.

[jgisonfire]

10 minutes ago, Johnny Ola said:

DEF?  Could you please be a little more specific.  Thank  you.

It's not used on gas trucks. On Diesel trucks there are 2 different tanks. One for Diesel, and one for DEF (Diesel Exhaust Fluid, I think). The "Button" is where the other tank inlet is..

[Johnny Ola]

Thank you very much for the answer.  Yes I have a gas truck.  i guess the what I thought was a button was where the DEF goes if the truck was a diesel.

[Booger T]

This is what it looks like.

[Johnny Ola]

Thanks for the reply and pic.  Very helpful.  It is one these situations where GM used a part for more than one application When used for only gas they covered up the other hole with what looks like a big button.

[Booger T]

Yep, no problem