89 V6 4runner check engine light question

[boscounderfoot]

My check engine light comes on only after the truck has been warmed up sufficiently. No stumble or loss of power, no unusual smells, smoking or anything else. Just the light. This wouldn't be a big deal, but I have to E-test in Colorado and the check engine light is an automatic failure here. Has anyone out there experienced anything similar to this?

Thanks in advance.

 

[03vrod]

Do you know how to check the codes?

 

[boscounderfoot]

Jumper with the paper clip yielded a code 21.......O2 sensor right?