Check engine light been on. I checked gas cap the other day and it stayed on. I will put premium fuel in next time i fill up. It's been on for about a week. Any ideas to cause or solution?
P0420 is probably the most common code seen. It refers to "Catalytic Converter Efficiency"
Basically, it Engine Control Module (ECU) monitors the chemical constituents of the exhaust, both before and after the catalytic converter. The Catalyst is really a small furnace that reburns the exhaust and adds more oxygen where necessary, to eliminate harmful emissions and convert them into [hopefully] mere carbon dioxide and water.
If the ECU doesn't see the proper changes in the exhaust, eventually it will set the Check Engine Light with a code of P0420.
While being one of the most common codes, it can also be one of the most inaccurate. Perhaps your catalytic converter is failing, or "poisoned" from chemicals that were not supposed to be in the exhaust. More likely is the the rear oxygen sensor is failing or contaminated, giving false reports to the ECU about the catalyst health. However, unless your 2011 Equinox has a great deal of mileage, I doubt either of these explantions. The code can be cleared for free by a local auto parts store, or you can purchase or borrow a scan tool very inexpensively that will allow you to clear this code.
You can also complete several so-called "drive cycles" GM Example in an attempt to clear the code, but this can be a considerable time and effort sometimes.
You might also purchase one of several "magic juice" solutions at the auto parts store, which can clean and improve, to a limited extent, a tired catalytic converter. But a long steady highway drive should do the same.
If the Check Engine Light goes away but later returns, further diagnostics will be necssary due to the ubiquitous nature of this code.
Other posters are correct: if the catalyst needs to be replaced, it may be covered under the 8 year / 80,000 mile extended emissions warranty.
There is actually a letter that was sent out (I also have a 2011 Chevy Equinox with this issue and just had my cat. conv. replaced because of it) saying there may be thermal damage or melting on it and if you have this issue to take it to your dealer to get it repaired. Did you get that letter?
It can be many things
I mean, way many things, as SteveRacer has already cited. The most common (but not unique) is a failing catalytic converter. Please note that often a bad catalytic converter usually is a symptom of a problem, not a cause. If you replace it without solving the source problem, it will fail again in very short time. If this is the case and this came on recently you can try to use a fluid to clean the emissions system to solve this problem, at least for some time to buy you time (or to do smog, if it is required in your jurisdiction). I used Seafoam once and it solved for a few dozen miles.
Using premium fuel will do nothing
Only use the specified fuel grade for your car. Higher octane level in the gas is to prevent it to flashing prematurely in a high compression engine. If your car uses 87 gas and you put 91, you will just be wasting money.
Check if the warranty is still valid for the catalytic converter
In the United States (should be your case, right?), the catalytic converter is warranted by law for 8 years or 80000 miles (whichever first occurs) and if your car is within this warranty it is illegal to remove the catalytic converter yourself. You have to bring to the dealer and they should do it for free. I think that in some states (like California) the warranty is even longer.