Paul

Les comment re Toyota sensor has reminded me that Toyota used a unusual and unique sensor I think it may be simple wide band sensor,introduced about that time. (Edit I think toyota called this a lean burn sensor.)

google lean burn oxygen sensor and do some research, but looks like that constant 0.45 is good

hopefully some one more knowledgeable will give better information on its working and expected signal output.

It could possibly explain your unusual sensor output

I remember that for a long time these sensors suffered from failed heater circuit and where not available on the after market, but I have more recently success with blue print vehicle specific units

Cheers Aidan

I