Back in October 2011, many members here kept me from free diving off a bridge over a dvc500 problem. Great team here. While my problem isn't exactly the same as yours, maybe you can pull something out of reviewing the thread:http://nepacrossroads.com/about21985.html
My problem was a pinched pressure tube and it was my fault. I was getting error codes but you didn't comment if you see any.
Take a look at the thread.....and keep asking questions !