Hello welcome to the site I am Dino and will be able to assist you on this.
have you ran a evap test using the scan tool yet ?
have you used the evap smoker to see if their is a leak ?
Yes and yes. Originally, it read major emissions evap leak. Now it reads Purge Flow Fault.
Had 2 smoke tests done at GM dealership. they found no leaks and suggested new gas cap.
ok i have been looking to see if their is a service bulletin for this but it's all clear.
I'm going to reopen this and see if a gm tech has ran across this at the dealer.
It seems that many people who own GM's have run into a similar problem with check engine light staying on. Can't understand why GM hasn't figuired this out yet. As the vehicle runs fine, it wouldn't be much of a problem except when you need inspection...then it won't pass. After changing the battery, the light stayed off for 2 weeks and more than 600 miles.
This is nusence!
Greetings and Welcome to Just answer.
Have you checked the purge solenoid on the top of the engine?
Ok, was there any dirt or dust in the vent solenoid when you changed it?
Ok, If there is dirt plugging the purge line back to the engine, if the valve on the engine is plugged or if there is a wiring issue at the valve on the engine, this will be the result.
The light goes out because removing the battery resets these computers. The could be electrical and forgive me if I don't sound sure, I cannot put my hands on your vehicle to do the testing myself. There is a quick test. Find the purge valve on the drivers side of the engine.
Take the line off that goes to the tank. With the engine running, see if there is vacuum there. If so, take the electrical connector off and see if there is vacuum there. If so, replace that valve. If not then you have a wiring issue or the PCM.
I encourage you to try these and let me know. We can continue here and get this solved. And add as much detail as you can in your replies, that helps me out on this end.