The 1998 S70 has been accumulating a few little problems I need to fix, but most recently the lambda light came on, and I used the ScanGauge to find code 133 - Os sensor. I found replacement info on Bay13 but How do I know if it is the front or the rear that needs replacing?

Also there is a mystery electrical problem where the lightbulb-out indicator sometimes comes on and sometimes goes away, and the left turn signal sometimes flashes fast but sometimes normal. I have not been able to locate the problem - anyone else have this?

Thanks in advance!