O2 sensors were replaced, catalytic converter installed.
Drives good.

Yet check engine light turns on after restarting.

Anyone know why this is happening?

 

Because something is wrong. What code is it setting?

 

Thats a good question
Got any expertise on the sensors

 

Run down to Autozone or the like and have them scan it. Mine was throwing MAF and 02 simultaneously and both were responsible for some stalling problem I was having.

 

Find a friend with an ODB-II scanner or a local autoparts store that will scan it for free. Makes no sense to pay anyone for pulling a code for you. If the 02 was bad you would notice driveability performance issues. But since you say it drives good then its probably something else. What is your idle like? Smooth or Rough? When was the last time you reset the computer?? Maybe its an old code.

Also check all visible electrical connectors under the hood for one that may not be plugged in all the way. Also check your vacuum lines for possible leaks.

 

Most major chain auto parts stores in the USA will pull OBDII codes free when you ask them. It is almost zero effort, because everyone in a city drives by a parts store or ten every day.

The<u> first step </u>is "The code is ____"

Everything everyone says until we know what fault the computer is throwing, is a waste of time.