1990 engine light on

[WAZ]

when I bought my 1990 the engine was on. It comes on after running for about 3 minutes. Always the same. Does this sound like and o2 sensor? Can shops read the codes on a 1990?

 

[sandealer]

It was the O2 sensor on my '96. Different elevations would change it too. But I replaced both 02 Sensors (not sure on the '90) and all was good.