Same problem here
I am having the same problem with my 04 model. The thing is that I am not very experienced with automechanics and I am having to take my vehicle to a shop for every repair. I have deduced that it is not the heater core(I dont have antifreeze leaking in my floor boards) and people have told me different things. The tester at autozone said that my Ambient air temp sensor is out, but I dont have a temp gauge inside my van that tells me the outside temperature. I have had my radiator, intake manifold gasket, and a gasket leaking transmission fluid replaced in the past four months, among other things like brake pads etc. This is just driving me crazy because my heater was just fine last year. Any help would be greatly appreciated because it costs over 70 dollars to put it on a diagnostics machine.