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Solved 02 Sensors: What They Graph Like


Moderator Emeritus
January 26, 2004
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City, State
Mechanicsville, Virginia
Year, Model & Trim Level
2004 Acura TL
This thread is more of just how 02 sensors are suppose to look like on a graph. These graphs are from a Snap-On Modis on my '00 Explorer 4.0L (VIN E).


If you look, this is just the beginning of the graphing. Both Sensor 1 02 sensors (before cats) are on the bottom while the other two are stacked on top for sensors 2 (after the cats). Two sensors should be jumping back and forth rapidly (as shown on the bottom) and then the other two (after the cats) should be pretty stable.


The picture above has more elapsed time on it and you see two drops/jumps on bank 1 sensor 2 -- that is the computer switching to OPEN loop. Closed loop basically means the computer is changing Pulse Width and other fuel/air mixture values compared to the 02 sensors. In OPEN loop the computer is running on a pre-set value via computer. When you stomp on it (like the two times I did in the above picture) it'll go to OPEN loop which will give you optomized performance at WOT (Wide Open Throttle).


The above picture is a zoomed in image of the pass pictures which show you how often they are switching back and forth (from lean to rich). I hope all these pictures will help some people understand 02 Sensors.

For More information visit Glacier991's thread on 02 Sensors: http://www.explorerforum.com/forums/showthread.php?t=149917