broken/open circuit or module unit not working properly
also possibly bad/corroded ground wire connection
I had the same issue with my o2 Blazer as well. Mine had come on after replacing the brakes and calipers. I had to have the computer reset in order to have the light go out. But I was also told by a dealer that that is a common problem with the newer Blazers.
Looking for a Used Blazer in your area?
CarGurus has 1,343 nationwide Blazer listings starting at $1,995.
Search Chevrolet Blazer Questions
Chevrolet Blazer Experts