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What year, model, and engine do you have?
I see your information came through after the rest of your question. Sometimes there is a delay.
Let's see what codes are stored turning your engine light on. cycle the key from off to on three times ending with it on and watch the digital odometer display. Don't crank the starter, just off to on. The codes start with a P and have four numbers, there may be more than one stored. Write down any that you see and post them here.
This is a small leak in the evaporative emissions system, the system that stores fuel vapors from the tank and burns them in the engine. This leak can be as small as .010", not easy to find.
Since you've already replaced the gas cap we can move under the hood to the most common spot. Near the washer solvent bottle on the right side you will find the purge solenoid. It has two hard 5/16" plastic lines running to it and a 2 wire electrical connector. It's mounted just inboard of the headlight on the sheet metal. Follow these lines rearward. One will go to the engine near the back of the throttle body. The other one will follow the frame rail to under the airbox. It will then turn 90 degrees down and into a 2 1/2" piece of rubber hose, that couples it to a metal line. This hose is almost always the source of the leak on these. You'll probably have to remove the lower airbox to get to this area.
If that hose is ok move on to under the van. Check the lines from the tank to the canister on the left side near the engine cradle, and from the canister to the leak detection pump ust forward of it. replace any line you find with cracking.
If you can't find the leak you can take it to a shop. They will have a machine for finding these leaks. It taps into the system and pressurizes it with smoke. The smoke will leak out where ever the leak in the system is.