To find it, you'll need to consult a repair manual specific to your van's year and engine. The manual will have diagrams showing the exact location. You can usually find these online (often for a fee) or at auto parts stores.
Generally, however, you should look near the crankshaft pulley at the front of the engine. It might be on the engine block itself, or on the transmission bellhousing near the crankshaft. It's usually a small sensor with a single wire connector. Be careful when searching as the engine bay can be tight and hot.
