What is the little black plastic box behind the driver's side rear wheel? Has some hoses coming out of it. Important?

 

It's the charcoal canister for the emissions.

 

+1 to Rex. i dont know if it will kick the check engine light on, but it could. i dont think that MO does emission testing, so you might be ok. but i would look into getting it replaced. it has to do with the fuel tank and stuff.

 

It will definitely turn the SES light on. Most likely a P0455 will be set. You'll probably notice a fuel odor, but it won't affect engine performance, and you'll never notice a drop in fuel economy.

 

Ok. I did notice a little fuel odor since it appears to be a fuel line. I will look for a replacement online. Or can I just plug the hoses? The brackets that held it in place are rusted and have now been stripped ofd the truck due to a little off road adventure today.

 

The lines carry fuel vapor only, no liquid fuel. Until it's repaired correctly, you're likely to get EVAP DTC's.