Where are the o2 sensors at on 1989 Chevy truck 4x4 And how many?

On a 1989 Chevy 4x4 truck, there are typically two O2 sensors located in the exhaust system. The first sensor is positioned before the catalytic converter (upstream), and the second is located after the catalytic converter (downstream). These sensors monitor the exhaust gases to help optimize fuel efficiency and reduce emissions. Depending on the engine configuration, some models may have only one sensor, so it's essential to check the specific vehicle setup.