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Check Gas Cap - 2006 Pontiac Montana

I have a 2006 Pontiac Montana SV6 with 80,000 miles on it. Recently the dashboard warning “check gas cap” has started coming on. I have replaced the gas cap and cleared the code and it is doing it again. It seems like it is more likely to do it when the gas tank is 1/2 or less full but it also did it today with almost a full tank. The code from the computer said P0455, does anyone have any idea what this could be? I’m hoping it’s nothing major!
Thank you!

Are you in the habit of toping off the tank when you fill up?

Does the dashboard actually say “check gas cap”?

Yes, I do usually top off the tank when I fill up.

Yes, the dashboard says “check gas cap” but the check engine light has not come on yet.


This got lost on the second page, mostly because the pages number have gone, I suspect.

If you tend to “top off” the tank, then likely you’re heading towards the evap system needing work now. The canister will hold the fumes while shut down so they can be put back into the system rather than released into the air. Frequent topping off can fill the canister beyond it’s ability, and then your system needs to be repaired.

Can you elaborate on what type of repairs may need to be done? Is this an expensive repair?


The only thing I can find for that code is “P0445 Evaporative Emission Control System Purge Control Valve Circuit Shorted”. Codes are an indicator, and they are a place to start looking, not always the actual problem that needs to be fixed.

I’m not sure what you need to get fixed, nor how much it will cost. Maybe someone else here has an idea. If it is the evap system, then most likely it would be the canister that would need to be replaced.

My 05 4runner I had a code a couple of months ago…Read it with my scanner…then looked up the code in my shop manual…It was a Evap Emission Control error…There were several possible culprits…Mine turned out to be the Gas cap…but there are several things (including the charcoal canister) that could be causing this error.