Why is check engine light on?

You need the codes read then the diagnostics performed on the codes and then re[air or replace the defective parts.

I had a 2008 Toyota Avalon for 12yrs, it was a 1 owner Vehicle when purchased & I kept it for years after it was paid off. My engine light came on & I believe the code was regarding an O2 sensor (not surprised as a single Mom of 3 kids without any support it was constantly on E & driven w/gaslight on) I was unable to renew tags for over a year because it wouldn’t pass emissions testing. When it began to not start & also not be able to move shifter from P to R & sometimes it stuck in D. That’s when I traded for a 2010 Nissan Murano & I really loved both however I JUST paid the Murano off in great condition and only put 3,000 miles on the Vehicle after 4yrs, thanks to being able to work from home. I owned a 2008 Toyota Avalon for 12yrs, it was a 1 owner Vehicle when purchased & kept it years after I paid off the loan. The engine light came on & was told it was regarding the O2 sensor (not surprising) as a single Mom of 3 with no financial support, I would constantly drive with little to no fuel, many times I had to drive 35-38 miles w/gaslight on to make it to work. I decided to trade it in when I began having issues when I would try to start it & it appeared as if the battery was dead, however the accessory lights & radio were working. I began to have issues with moving the shifter from P to R & sometimes it wouldn’t move from D-Park. Not sure what the issues actually were as I traded for another vehicle & thank God I listened to my gut because after I left it with dealer, it never started again.