On Wed, 13 Aug 1997, Erik Rhodes wrote:

> 
> 	I just had a smog check done on my '78 bus and the smog check
> guy said the oxygen sensor was bad, thus misinforming the computer and
> making the CO output too high.  Is this right?  Putting in a new one
> hasn't affected engine running or anything, just what does this sensor
> do?

The O2 sensor is a little battery.  The "potential" difference that 
drives it is the difference between the O2 in the exhaust and the ambient 
O2.  A "rich" mixture drives the voltage toward the maximum of its output 
(around .9 - .95 volts) while a "lean" mixture drops the voltage down 
toward zero.  The computer reads the voltage output and adjusts fuel 
delivery accordingly.

Did you pass smog with a new O2 sensor?  If so, you were probably running 
rich (and the faulty O2 sensor couldn't tell the computer about it) 
which, if not too extreme, tends to imporve driveability.  So you might 
not notice significant differences in the seat of your pants, but the 
exhaust analyzer gives you a "pass" instead of a "fail."

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Tom Young               young@sherlock.SIMS.Berkeley.EDU
Lafayette, CA  94549    '81 Vanagon
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