That would be the sensor after the catalytic converter.
where is the secondary 02 sensor on a 2004 crv
After the catalytic converter.
It might be in the diagram of parts and places, if comes with it.
The 1994 S10 uses a MAP sensor, not a MAF sensor. We need to know size engine you have in that S10.
There are several O2 sensors on that vehicle and they are all threaded into the exhaust system at various points.
Don't know what year you have but on a 02 S10 4.3L engine it is located on the drivers side of the engine between spark plugs #3 & #5.
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.
Three altogether. Two upstream and one down stream.
All O2 sensors are threaded into the exhaust system at various points.
That is the pre - cat 02 oxygen sensor.
The one the ecm reads is located right next to the thermostat housing.