I just bought the Aspen. I've had a 4.7L Durango for 5 years and loved it but, wanted a bit of an upgrade and got an 07 Aspen. The MDS system worked when I first got it a week ago. Or, at least it seemed to. I was getting nearly 20 mpg. Now, the MDS is not working (verified with AlfaOBD). The only code it is giving me is P3400. Not much of a clue as to what's wrong. I used AlfaOBD to test the four solenoids and they all kicked on.

Any thoughts on what to check next?

 

wrong oil type low oil pressure MDS sednoid lifter or oil blockage