Problem with my Superduty.

2011 Ford F-350 dually. 67k miles bought new. When I get in truck and go somewhere the "service engine indicator " is on. And stays on. Next time stays off. Dealership says fault code P204B Ran point test suspect Def pump. Pump test Ok. They suggested replacement of pump, 1200 bucks. But they aren't positive that is the problem.

Anyone else had anything similar?