The CEL in my 2002 OBW (AT) came on couple times last week and the code read P0138 (O2 sensor-High Voltage-Bank 1 Sensor 2). I have Borla headers with Stromung cat-back and mid-pipe installed over a year ago. To avoid O2 sensor problems, I also installed a spacer in the rear O2 sensor. Any idea? Would replacing the sensor (front or rear) get rid of the problem?

 

Thanks :-\

"To avoid O2 sensor problems"

...Apparently, didn't work

Are you sure no air is getting in between the engine and the second O2 sensor? That can cause a CEL, too.

 

What's the spacer look like? Maybe try removing it.

 

Any idea how old the O2 sensor is? However unlikely, it's possible the sensor genuinely is worn out.