Upstream downstream oxygen sensor

[Jacksondallas]

Is there a difference between the upstream and downstream sensors or can I use universal sensors for both? I have a 2012 forester.

 

[Jacksondallas]

Sorry. Oxygen sensors

 

[wv109323]

The wiring harness is different on my 2009 Forester(color and terminals) Other forum posts recommend Bosch or OEM. I went the cheap route and continue to have Check Engine Light.

 

[Dick Foster]

Is there a difference between the upstream and downstream sensors or can I use universal sensors for both? I have a 2012 forester.

Usually no, except for lead length maybe.
There are basically two types of O2 sensors, narrow band and the much more expensive wide band sensors.
The narrow band units put out a voltage of about 1 volt max but spend more time at about 0.5 V while wide band units put out between 0 - 5VDC using extra electronics.
The narrow band units typically only indicate lean, rich or stoich while wide and units have a more liner and proportional response.
As they are much more economical, most stock O2 sensors tend to be the much cheaper narrow band type.
The after CAT sensor has a far less dramatic output swing as it's only there to ensure that the CAT is working as it should, while the precat sensor is used by the ECU to constantly tweak how much fuel the engine needs along with other sensors like MAF, TPS, water temp etc. Therefore it's output constantly varies up and down between rich, lean and stoich. Or the perfect amount of air to fuel of 14.7 pounds of air to every pound of pump gas. Different fuels have different stoichiometric ratios.
As you might suspect, nitro racing fuel requires much more fuel or richer fuel ratios than does regular pump gas therefore more power.