I'm getting P133 and P171 codes on my 96 Contour. It had 86,000 miles and seems to be running good. Had the MAU replaced a month ago and within 100 miles, the light was back on. Any suggestions for what it might be?

Thanks for any help.

PO133 - upstream O2 sensor slow response
PO171 - system to lean bank 1

I think its time for a new 02 sensor.

OK. Now the question I have is based on the code response of Bank 1. If I understand correctly, there are O2 sensors on each side of the catalytic converter. Which one is the Bank 1 sensor? I have the 2.0 DOHC 4 cyl model.

The next question would be recommendations for where to get instructions for replacing it.

upstream means before the cat, so its on the front bank (obviously because you only have 1 bank) and its the upper 02.

replacement is pretty much common sense. Get a wrench, unscrew it, unplug it. Plug in the new one, screw the new one in, your done.