The pre-cat O2 sensors are (from standing in front of the engine) to the left of the engine, on the top of the exhaust manifolds. The post-cat O2 sensors are seen from under the vehicle at the end of the exhaust manifolds.
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Bank 1 (one) is the side in front of car (Bank 2 is rear, firewall side) 02 sensor 1 is upstream, on exhaust manifold (02 sensor 2 is downstream, by cat. conv.)
02 Sensor, bank 2 no activity.
It is the first O2 sensor on the passenger side before the catalytic converter
usually 02 sensors are located on the catylac converter OR the manifold
Bank 1 is the driver side.
On the exhaust manifold, near the headpipe connection.
There is more than one O2 sensor in that vehicle and they are all threaded into the exhaust at various points.
On a 2000 Lincoln LS , 3.9 liter V8 engine : Bank 2 is the drivers side of the engine Sensor 2 is in the exhaust after the exhaust has passed through the catalytic converter ( downstream sensor )
where is the secondary 02 sensor on a 2004 crv
On a 2000 Lincoln Navigator : Bank 2 is the drivers side of the engine Sensor 1 would be close to the engine before the exhaust enter the catalytic converter ( upstream sensor ) Sensor 2 ( downstream sensor ) would be in the exhaust after the exhaust exits the catalytic converter
When a O2 sensor goes bad the check engine light will illuminate. The code set in the ecm will lead you to which O2 sensor is bad.