Greetings earthlings!

We have a capture of an air fuel ratio sensor on an 02 Toyota 4 runner 3.4.  This vehicle only has 1 a/f ratio sensor at the inlet to the convertor, and one O2 sensor at the conv. outlet.

We did use the new K110 microamp probe to get this capture.

This capture is part of our program to get totally lost on new things that are not broken, so when we see a broken one we know what is wrong.  At least in theory!  Vehicle is in for a maint. timing belt, with no performance problems or codes at all.

The amps go negative!  Anybody else ever see this?  It appears that the amps go positive when rich to a level of about 5.2 milliamps, and negative when lean to about -4 milliamps.  We did carefully zero the probe before we started.

The voltage, on the same signal wire, does not move at all.  perfectly flat.

Took a movie with the Modis.  About worthless!  Newer ones of these, like newer lexus, have a number of pids that help diagnose these.  

But on this one there is not much really available.  There is a pid for a/f ratiio voltage, it sits at 3.3 volts at idle, which is the same reading the pico shows.  But when you snap the throttle the voltage changes on the scanner, from about 3.6 volts to 3.0 volts.  Except that is not really happening!  Filtered data, not unfiltered data.\

And there is a pid for a/f ratio.  It sits at 1.00 at idle, and we got it to range from 1.02 to .98

How on earth (which is not my home planet) could we possibly diagnose this without a microamp capture?  

Anybody see any neat stuff in this pattern that we are missing?  

It is filtered, which I prefer to avoid, but it was necessary to get it nice and clean.

There are 2 captures of this, this filtered one and one similar with filtering turned off.  If anyone wants will gladly stick them on the drop site.

Thanks!

John and Mike

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if i remember the characteristics of this a/f sensor then the positive and negative amperage is normal.  obviously i've never captured one before, though  ;D.  the scanner is usually my best friend on these, but like you said there isn't always a bunch of pids to help.  i really gotta get one of these  :).  you guys must feel kinda lonely testing this thing by yourselves  ;D.

is this a broadband sensor ?

I seem to remember Frank Massey doing a similar test with the micro amps clamp & the signal high was lean & signal low was rich which tallies with your capture or near enough  :)

The AF sensor trace works opposite of the common O2 sensor, high is lean, low is rich.

John,

That looks a lot like the AFR in the 2008 Miata posted here:

http://www.autonerdz.com/cgi/yabb2/YaBB.pl?num=1274201795

In that one, we had a scanner AFR current PID on our Modis.  We oriented the microamp probe so that the current deflections followed the scanner PID.

There are other methods to try to read current on these, but they all involve breaking the circuit and none of them work as well as this or are as easy to do.

crackerclicker wrote on Oct 5^th, 2010 at 7:18pm:

the positive and negative amperage is normal

i should probably clarify that statement  :).  it's not so much negative amperage as it is amperage flowing the opposite direction of the amp clamp's orientation.  sound right?  :)