o2 Oxygen Sensors

What do these o2 sensor things do?

They measure the amount of Oxygen in your exhaust and convert that into an electrical signal that the vehicles computer can understand. That way the computer can automatically adjust the fuel based on changing factors.

Which is Bank 1 Sensor 2?

Bank one always designates the side of the engine with cylinder number 1 on it. Bank 2 is always the side of the engine that has cylinder number 2 on it. Here is a diagram that should make it super easy for you.

What brand o2 sensor should I buy for my Astro/Safari van?

I'm not a this brand or that brand kind of guy. In fact some of the aftermarket stuff is better than the OEM stuff that was originally installed. In this case however, my only advice is that for o2 sensors, stay away from Bosch. There are numerous years where these problems have been reported so I would just skip Bosch o2 sensors for our vans 100%.