on my way to work and eml light came on ! got mate to scan using a modis and pulled code p0031 bank 1 02sensor circuit low ? clear code but comes straight back on ! car is standard 2004wrx with 92k . adl/blue print sensor is £165 +vat ! . i take it its the sensor in drivers side lower manifold and plug joins near top suspension turret ? .
in live data it shows sensor sticking at 3.397 v and open loop constant ? is it gonna be sensor or is there a fuse / relay !? thanks

 

Was 02 sensor heater fault so fitted new one and job done ! oh and from dealer they want 297+vat !! if you ever need one either fit a dealer one or a blueprint/adl one as cheap ones wont do the job or code clear .
If you get this fault code just make sure you test the heater circuit of your old sensor to measure resistance between the heater wires and that you have ecu voltage and grounds at engine plug .

 

you can source OE Denso ones at far less than the ADL costs if you know who/where to ask??