[DeTomaso] NPC - Testing O2 Sensors

[michael frazier]

I know upstream sensors should show a square wave between 0 and 1 volt on a scope, and downstream sensors
should show a relatively flat wave.  
 
I'm viewing these on one of the small hand held ODB scanners set on "live" readings.  I'm seeing a triangle wave,
sharp peaks, within the correct voltage range.  
 
Does anyone here have experience with these units and know if they have a sampling rate that would actually show
a square square wave?  I'm getting the very vague P0240 code on my Tahoe and wold like some more input before
I begin throwing money at it.
 
Thanks
Michael
Big Bend Open Road Race in April!!!