I was unable to locate, in the factory service manual that I have, anywhere that it specifically stated 70% Federal, 85% Cali when key on, engine off...thats not to say that I disagree or do not believe the information on the website..
Ensure that you have your probes for the meter in the correct places: +pin3, -pin2 of x11 connector on fender of car...and then retest the voltage..
Ensure that you are using the formula properly:
Duty Cycle = [1 - (V{pin 3}/V{max})] x 100%
I did a fair amount of work on this topic, here is some information on it, you might find something helpful in there...
http://www.peachparts.com/shopforum/showthread.php?t=253393
Ignoring the not reading 70%, have you checked your duty cycle with car running @ operational temp?
If you do this and get a 50% then its certainly the O2 sensor. Alternatively you could disconnect the O2 sensor with the car at operating temp and check its output voltage, its should be oscillating rapidly. If it is a fixed value, time for replacement.
Here is the chart for errors generated during that and courses of action to fix problem:
http://i98.photobucket.com/albums/l250/MafiaNicky/50006pdf2.png
Hope this helps...