Malfunctioning and Failed Oxygen Sensors
Oxygen sensors can fail when the sensor's ceramic element is exposed to certain types of silicone compounds or when an oil-burning engine leads to the sensor becoming oil-fouled. Also, a small amount tetra-ethyl lead in the gasoline can kill an oxygen sensor. Over-the-counter fuel additives, which are not "oxygen sensor safe", can also kill an oxygen sensor.
Failures can occur either: 1) instantaneously at the time the contaminant contacts the oxygen sensor, causing a dead sensor, or 2) gradually over a period of time. Gradual deterioration results in a "slow" sensor which does not react as quickly as it should, causing the catalytic converter to perform less efficiently. This can lead to premature failure of the catalytic converter.
"Slow" oxygen sensors can cause a drop in fuel economy of 10-15% and cause excessive exhaust emissions and poor drivability. Unfortunately, the symptoms of a "slow" oxygen sensor are not always obvious to the vehicle owner, unless the vehicle fails an emissions test, a decline in fuel economy is noticed, or drivability problems occur.
A "dead" sensor can be detected with a relatively inexpensive digital volt-ohmmeter. A "slow" sensor can only be diagnosed by using a digital oscilloscope or scope meter. Most installers will probably not be able to spot an oxygen sensor problem until it is too late, and the catalytic converter is already well on its way to failure.
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