Which engine do you have? I can find only one coolant temperature sensor. There appears to be no separate sensor used for the gauge so I don't know what you're referring to by "fan sensor".
You gotta love the insane engineers who took a simple reliable gauge circuit and made it ridiculously complicated. The coolant sensor that feeds the Engine Computer to run the radiator fan now appears to also be used for the gauge. The Engine Computer sends the information for the various gauges on the data buss to the Body Computer, and the Body Computer interprets that information and sends it to the instrument cluster which is another computer module. That's right. Instead of a gauge and a sending unit, there's three computers involved now.
Since the Body Computer is a known high-failure item, it's the first thing to suspect. If the radiator fan turns on at the appropriate times, you know the temperature sending unit and Engine Computer are working. That leaves the Body Computer and instrument cluster. The cluster also develops a common problem of dead gauges due to broken solder contacts on the connector pins, but if the other gauges and functions are working, the cluster should be okay. If the radiator fan works, my vote is for the Body Computer.
If you're going to try a used computer from the salvage yard, be aware there are issues with the anti-theft system. If your van has that system, you can use any computer. If the engine doesn't start, you must program the computer to recognize the system. You do that by turning the lift gate lock cylinder with the key to the unlock position. If your van doesn't have the factory system, you must get a computer without that programming, otherwise the engine won't start.