I just recently had the P3400 code on my 2007 Dodge Ram 1500 Hemi. I had just bought the vehicle with 260k miles on it.

It is most like an oil maintenance issue.

How to diagnose:

After receiving a P3400 code. Reset it. If the P3400 reappears almost immediately from driving, then it is most likely a bad solenoid. If it reappears almost immediately I would test it again.

However if you reset the code and the P3400 does not reappear immediately. Then it is a oil maintenance issue. You'll be driving along and all of the sudden the engine will feel like it is hesitating then the code will appear. My code was popping up after driving about 5-15 miles. I had reset it a few times so I knew the interval of when the code would pop up.

What ever you do....Do not waste your type replacing the solenoid until you have done a full oil and oil filter change.

I did an oil change and the code has not popped back up. I have driven for about 200 miles and I'm confident that was the issue.