I also have a 1997 Express and had the same problem. It's a bad ground. These vans are known for it. I watched a youtube video for a fix. I used a jumper wire from the socket to the body of the van on each side. It corrected the problem and the lights work great.
Once my wife and I were on our way home from Traverse City and I pointed out to her an old Airstream trailer that looked like new. As we passed the trailer we seen it was being pulled by a '56 chevy convertible!
I got the same notice for my Silverado 5.3, but before I received the notice my wife was driving and the throttle position sensor went out. The truck would not go over 15mph. Dealer replaced the sensor and there as been no other problems.