Getting a P0131 code on a 2004 9-3 Arc w/240,000 miles. Searched this forum and didn't find any useful information. Are there other things, besides an O2 sensor, that can cause this code? Is there an easy way to test the O2 sensor or should I just go ahead and change it out? Sorry if these are stupid questions, but I mostly work on diesels that don't have o2 sensors.

What I have done so far...

Checked and car reads 0 volts on code reader at bank 1 sensor 1.

Took car out and monitored while wife drove.

Getting fuel sys stat of 0l,fault from Cl,USING HO2S. The lt and st fuel trims stay pretty much a -0%. Watched voltage at o2 s1 and once it warmed up got a voltage at about .58 - .8, but periodically dropped to between .1 and 0.0. Can't tell if fuel status changes before or after the voltage drop and the P0131 code being set.

Thanks in Advance.