Hi Tony Good topic, Your initial post explains Titania perfectly well.The reference in Mark Warrens article about reading backwards refers (I believe) to the comparison betweem Zirconia and Titania.Pico,s explanation is also incorrect in the second paragraph of Marks post. Titania are resistance change sensors which have a very high resistance lean and low resistance rich, they are supplied ref voltage from the ecu via a calibrated resistor,-in effect two resistors in series, the titania sensor being one of them. Your electrical knowledge tells you that in that situation, if you could measure the voltage between those resistances(which is what the ecu does)then If the resistance of the sensor goes high then so will the voltage, therefore high voltage lean and low voltage rich. I fail to see how this principle can be reversed in a titania sensor to change the voltage/resistance/oxygen relationship, though I am happy to be proven wrong. nothing posted so far though has done that. Ed Kaps