https://en.wikipedia.org/wiki/Oxygen_sensor#Automotive_applications https://en.wikipedia.org/wiki/Oxygen_sensor#Automotive_appli... It looks that some O2 senso

https://en.wikipedia.org/wiki/Oxygen_sensor#Automotive_applications https://en.wikipedia.org/wiki/Oxygen_sensor#Automotive_appli... It looks that some O2 sensors that don't require a reference have been used (titania sensors) but even though they have some advantages, they are less precise and mostly obsolete.