Hello and Thank you for choosing Just Answer.
Before I can assist you, I will need to know a little more information:
More than likely the sensor on the side of the transmission is bad. But first I would take a quick look at the connector and the wires as sometimes they can melt due to the heat underneath the vehicle.
This is the sensor you are looking for:
one last question, I went to look under the transmission and could not find the sensor box that the arrow points to. Do I need to view the diagram as if I was laying under the van?
The sensor is on the drivers side of the vehicle in the side of the trasnmission. Maybe this picture will better help you out: