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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29501
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Fault code P0496 check engine light on - vehicle runs fine

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Fault code P0496 check engine light on - vehicle runs fine

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 ?

Customer: replied 6 years ago.

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.

Customer: replied 6 years ago.

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?

Customer: replied 6 years ago.
On the trailblazer there is a solenoid near the gas tank on the passenger side. It was replaced. If there is a purge solenoid on top of the engine, I am not aware of it. Do you know the exact location?
Ok, confirm this is the straight 6 not the V6?
Customer: replied 6 years ago.
It's listed as 4.2 liter L6 Engine - Fuel Injection - Feedback Fuel System

Ok, was there any dirt or dust in the vent solenoid when you changed it?


Customer: replied 6 years ago.
It was dusty but it's a sealed unit. The mechanic said it wasn't overly so. After it was changed, he cleared the code. The light came back on in a short period of time. The longest the light has been out has been when I changed the battery. Light was out for 2 weeks and 700 miles.

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.


Customer: replied 6 years ago.
I appreciate the effort but the last time I was here, the mechanic said it was the Vent Selenoid or the gas cap. Neither corrected the problem. You don't sound real sure of the answer. Why would the light go out after replacing the battery and stay out for 2 weeks and 700 hundred miles? Is there a sensor in the vehicle that could be bad? Could it be electrical rather than mechanical?

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.


Customer: replied 6 years ago.
So, you are saying that if I try these and they don't work, we can continue until we find a solution?



Customer: replied 6 years ago.
Will I be able to ask for you directly?!
Yes, on this issue, simply reply to this thread. If you want me to answer your next GM or GM product question, please put "For GMTECH Cam to Answer" and I should get it.
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29501
Experience: GM Grand Master Technician 2007. 14 years experience.
GM Tech (Cam) and other Chevy Specialists are ready to help you
Customer: replied 6 years ago.
Haven't had time to get it checked out yet. But have changed fuel neck, fuel pump, rear solenoid and gas cap. No luck yet..light still on but vehicle runs fine. Next step is to check front engine solenoid.