Diagnostic error codes?
 

Hiya,

My 2005 Scion xA has had the Check Engine light come on a couple of times lately, and since I own a ScanGuage II, I checked the code number: P0138.

I looked it up and it is a "high voltage to the oxygen sensor"

OBD-II Trouble Code: P0138 Oxygen Sensor Circuit High Voltage (Bank1, Sensor2)

Does this affect my mileage? It seemed like it does... Do I need to replace the oxygen sensor? Or is there something else that can correct this? I have a zero deductible extended warranty...

It really shouldn't effect mileage. The front o2 sensor is mainly the only one the engine uses to maintain correct air/fuel ratios. The rear one mostly there to ensure the CAT is doing its job. Ironically, the rear O2 sensor usually goes bad before the CAT.

My guess is the O2 sensor went bad. I would take it in to get looked at since you have the warranty.