Check engin light is on?

Hi,
looks like there is a sensor on the filler cap/lid side.
which is faulty and not sending correct signal to the main computer in the car.

The engine light comes on from some kind of problem with the engine. It could be a sensor of any kind. The best thing to do is go to a place like AutoZone and have them scan it and find out what is going on. One thing you could check is the gas cap, if she put gas in it and didn't get the cap on tight it could set a code and turn on the light. If you get the cap on right the light should eventually go out. Please rate my answer so I get the points for answering your question.

Hello, have you tried to unhook the negative side of the battery for about 10 minutes and then go from there . It should reset the computer completely .

It may go out on its own, the next time the computer does a routine system check. If two or three runs around town over the next few days doesn't clear it, only a dealer or a good mechanic with the proper scanner can turn it off.

the cap most likely set an evap code in the computer have it checked with a scan tool.if the cap is on tight then just clear the code and the light will go out.

I hope they reset the code for you.
Most times when that code occurs it's because the gas cap wasn't put back properly when you got gas.
If they didn't reset it take it back and ask them to reset the code.
If it doesn't come back you know it was a loose gap cap that tripped. If it does then you need to start looking closer. 1st make sure the cap seats well and seal the filler tube. If not replace it.
A small vacuum leak can be difficult to find but you should start by examining the vacuum hoses for cracks ESPECIALLY where connect to their fittings. If cracks are found just cut the end off and reinstall the hose.

The code needs to be reset. The code you got was most likely "emission leak medium" this happens if the gas cap is left loose. If the code is reset, and you tightened your gas cap it should not come back. If it does, then get back with me and I can walk you through some steps and parts that will have to be checked, but I am 99% sure its only your gas cap, Happens to me all the time, and I just reset it after tightening my cap. Thanks.

Have vehicle scanned for codes at Autozone its free and do the repairs the codes list.

Make sure your gas cap is tight, at least 5 clicks, sometimes a gas cap that doesn't seal tight will trigger the Check Engine Light. If the light stays on you will need to pull the Trouble Code from the ECM (Computer) using a OBD II scanner.

PO455 is a large evaporative fuel leak. A bad fuel cap is ONE of the things that COULD be the problem. Fuel system cleaning only lightened your wallet. Reading your post is confusing. Did all this start AFTER the Valvoline Wallet Flushing? If so , they left something loose or disconnected. I would find a qualified repair shop to fix the problem, and if it has anything to do with what Valvoline did, make them pay the bill.