Hello I will help you with your question,
Do you know what codes have been set when the light was on?
There are hundreds of reasons the check engine light can be turned on so you need to see what code is being set. It may not be related to the vent valve though that was a common issue with this truck.
Autozone will pull the stored codes at no cost to you in the hope of selling you parts. Have them read the code and let me know what it is and I can help you decide what has to be done to keep the light off. More testing or a part replacement may be needed but reading the code is the first step. Do not disconnect the battery between the time the light is on and when you have the code read.
Let me know what you get so I can help you