I have a a 99' S70 T-5. It's got about 184K on it. I have had the car for about a year now.
The check engine light has been on for most of that period. Obviously, I am not passing an emissions check and my understanding is this is related to the Mass Flow and the front and rear O2 sensors. Yesterday we put in the front O2 as the original one was shot, the rear one was replaced about a year ago. The check engine light was off for the last day and now it's back on.
Any experience or general advice on getting this guy to run smooth and pass emissions testing?

 

You can start by helping us help you... What codes do you have in the ECU?

 

I had it plugged into the computer and there are two: PO134 and PO135. I'd love to get this baby running smooth.
Is it possible the front Bocsh O2 sensor installed last Tuesday was defective or is it more liked that there is another culprit that caused it to go bad?

 

I'm not sure. Maybe someone else will chime in and help. Was the sensor new? You can also check the 850 section for help.

 

To the general community: Could the Mass Air Flow sensor be the culprit?

 

Not the MAF. P0134 is a failure of the O2 sensor to send any signal, and P0135 is a failure of the ECU to register continuity in the heated element of the O2 sensor.

BOTTOM LINE:
Your new O2 sensor was hooked up wrong, Boss.

 

Could be, but I have had 02 codes that were cleared by a new MAF!