Dont know about e-brake but some times depening where your truck was bought some stuff is enabled and some stuff not(weird) i think its a east coast west coast thing

 

Iv got an 05 and had the dealer engage it.
COntact the dealer and inquire about your 04.5.
It should have it.

 

I think I remember reading on a forum that the 04's may need a flash to install the option first. Then have the option enabled by another flash.

I don't have an E-Brake and mine works? Maybe if you have the E-brake it needs to be engaged for it to work?? Typical of large company thinking if so. I use mine to keep cool as well when it's warm out. Raise the engine speed a/c works much better.