What is this? (Under Hood)

[Rcpritchard1]

I have a 2009 Ram 1500 with 5.7. I was wondering what this is. It has a white cap just to the left of the battery. I’m guessing some kind of fuse?

 

[Atcer2018]

Looks like some sort of breather vent. Can you follow the hose and see where it leads?

 

[Tulecreeper]

Looks like a plug for a vacuum line.

 

[crash68]

Most likely the breather for the transmission. The transfer case breather is on top of the case and the axle breathers don't come up into the engine bay very far

 

[Jim BB]

looks like a vent tube ! my best guess is for transmission or transfer case!
follow tube and see if you can see where it goes

 

[Dodge 1500 4X4]

Is it a 4x4 could be a vent for the front Diff.

 

[Rcpritchard1]

Yes it’s a 4x4. Could be a vent. The white cap is loose and spins around. I didn’t think of a vent. Thanks for you’re input

 

[Sherman Bird]

Yes it’s a 4x4. Could be a vent. The white cap is loose and spins around. I didn’t think of a vent. Thanks for you’re input

It's a vent cap which, in theory, allows hot expanse air out, but closes via float when it is under water!

 

[18CrewDually]

Yup , vent for the front differential. The other end is on the front cover. Pic below.