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.

When the computer sees a fault that makes it turn on the CEL, it also disables traction & stability systems, and that's likely why the VSC light is on. Yes, you need to have codes read to fund the problem and have it fixed. And if this is the first problem you've had with your fourteen year old Avalon, you're average and should be happy about this.

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.