1989 Silverado with 5.7 V-8. Located an O2 sensor on rear of exhaust manifold on drivers side. Can't find anymore on exhaust system. Does this engine have only one?

 

I believe it does only have one. My 1995 only had one as well.

 

Yeah I think they started the whole 2 pre cat and 1 post cat sensor in 96-97

 

Thanks for your replies that only one O2 sensor is used on this model. The CES light is infrequently coming on and I suspect the O2 sensor is the culprit. Since there is only one it will be cheap to replace. Thanks again.