This is the downstream O2 sensor. This is how you tell upstream from downstream. The O2 sensor that is closest to the engine is the upstream sensor. Then there will be the catalytic converter going down your vehicle's exhaust from the engine to the tailpipe. The catalytic converter is, I repeat for emphasis, is the "stream" in upstream and downstream, and then the downstream O2 sensor. So closest to engine upstream, farthest from the engine and after the catalytic converter, downstream.
Thursday, April 11th, 2019 AT 8:00 PM