Regarding check engine light

Really what you are doing is nothing and it's not going away by disconnecting the battery terminal. that light comes on for a reason. it lets you know that you have a problem somewhere. you need to take it somewhere and have the code(s) read.most parts stores will check it for free,or take it to a repair shop with a good scan tool,and that ain't free!

In addition - disconnecting the POSITIVE cable while the negative cable is still attached is a mistake! Can lead to a short circuit and destroy sensitive electronics .... ALWAYS disconnect the NEGATIVE cable FIRST.. As stated - seek hands-on help from qualified personnel.