1998 6TS prefix 3406E is giving me Code 21

1998 6TS prefix 3406e is giving me a code 21 on the dashboard. Looking into it, its low voltage code something about 5v?
Do i just start unplugging the 3 wire sensors until the check engine light goes away? The truck was running fine, I had just made my way from DFW to Knoxville, Tn and have had no issues. I put fuel in Knoxville at the speedway and was continuing my way east when my exhaust manifold gasket let go. I limped the truck from the side of the road to a truckstop and no check engine lights where on.
This morning on my way to a shop to get my gaskets done my check engine light came on and derated my truck. Now my engine fan stays on, I cant build any boost and I have no power. Could the exhaust comming from the gasket leak have caused some kind of short with the wires or sensors under the turbo near the water pump?