> Is there a way to test O2 sensors?
A working O2 sensor puts out 0.1-0.9 DC volts. This can easily be measured
with a digital voltmeter (even my eL-Cheapo Harbor Freight voltmeter). With
the engine warmed up (the sensor has to be hot to work), find the lead for
the sensor. (There may be 3 or 4 leads if the sensor also has a heater built
in.) Connect your voltmeter's positive lead to the sensor lead & the
negative lead to ground. Do this leaving the sensor connected to the
vehicle's wire harness so the computer will remain in 'closed loop mode'
(receiving & sending signals). Thusly connected start the engine. Run it at
2000rpm for a minute or two to make sure the exhaust & the sensor is fully
warm.) At idle a working O2 sensor will be putting out an average of 0.5V.
If the computer is in closed loop mode the measured signal will constantly
vary as the computer richens/leans the mixture around the 'ideal'. If the
reading is steady then the computer will usually assume the sensor is not
functioning, ignore its signal and default to a pre-programmed fuel map -
typically slightly richer than ideal.
If the sensor is more than 60,000 - 90,000 miles old it is likely at the end
of its useful life. As they get old they get 'slow'. When it gets really
slow the computer ignores it.
Eric Russell
Mebane, NC
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