Technical information from Bosch - Recommended Check/Replace Intervals
Bosch Recommended Check/Replace Intervals
Many vehicle manufacturers do not provide recommended check/replacement intervals for oxygen sensors, because it is hard to predict when an oxygen sensor will fail. OEM oxygen sensor manufacturers, such as Bosch, work hard to ensure that oxygen sensors last as long as possible. The latest designs can last over 150,000 miles under laboratory bench-testing conditions! But out on the road, sensors are subject to very difficult conditions which can cause sensors to fail earlier than they do under laboratory conditions.
For example, 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 of poorly refined gasoline can kill an oxygen sensor, as can the use of some over-the-counter fuel additives which are not “oxygen sensor safe.” These failures can occur either: 1) instantaneously at the time the contaminant contacts the oxygen sensor, causing a dead (totally nonfunctional) 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, thus causing the catalytic converter to perform less efficiently. This can lead to premature failure of the catalytic converter, which is an expensive item to replace.
Under conditions of gradual deterioration, “slow” sensors eventually become “dead” sensors. Unfortunately, the symptoms of a “slow” or even “dead” 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 if driveability problems occur.
Furthermore, while a “dead” sensor can be detected by the do-it-yourselfer with a relatively inexpensive digital volt-ohmmeter, a “slow” sensor can only be diagnosed by a more expensive oscilloscope or scope meter. Thus, the do-it-yourselfer 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. As part of a sensible preventive maintenance program, we recommend that either:
1) oxygen sensors be checked on a lab scope or scope meter by a professional automotive technician at intervals specified in this catalog, or
2) oxygen sensors be replaced by the do-it-yourselfer at the intervals specified in this catalog. The “check/replace” intervals published in this catalog are not intervals specified by the vehicle manufacturer, but are instead recommendations based on our experience and knowledge of oxygen sensor technology.
One-wire and two-wire “unheated” type oxygen sensors should be checked or replaced every 30,000-50,000 miles. These sensors rely solely on hot exhaust gas to heat up to operating temperature, and therefore are designed to allow a large volume of exhaust gas to make contact with the active ceramic element. Therefore, these sensors are exposed to contamination, especially the “wide-slot” varieties found on Chrysler, Ford, and General Motors vehicles.

“Heated” type oxygen sensors have a built-in heater which heats the sensors up to operating temperature. Therefore, much less exhaust gas needs to contact the ceramic element, making these sensors less prone to contamination. “Heated” type sensors can also be located further downstream (closer to the catalytic converter), which increases their life expectancy by reducing thermal shock. In addition, the latest versions feature improved ceramic elements which are more resistant to silicone, oil, and lead contamination. “Heated” type oxygen sensors should be checked or replaced every 60,000-150,000 miles.

Can Use Possible Substitutions (Footnote # 71):
Sensors in each column are identical except for the length of the wiring harness. The sensor with the longer wiring harness can be used to replace the sensor with the shorter wiring harness. (details see link below)

Glossary of Terms
Air/Fuel Ratio,In combustion, the amounts (in mass) of air and fuel involved in the combustion. For gasoline engines, the ideal Air/Fuel ratio is 14.7:1.
Air/Fuel (A/F) Sensor See Wideband A/F Sensor. The term used by some sensor and vehicle manufacturers to differentiate wideband oxygen sensors from switching oxygen sensors.
Closed Loop Operation Closed loop operation for an engine occurs when the ECM is receiving inputs from all sensors. In closed loop operation, the ECM is able to vary the cycle time for the injectors based on the inputs of throttle position, air mass, and the amount of free oxygen in the exhaust stream. Typically, oxygen sensors are the last sensors to become operational, since they must be heated to an operating temperature of at least 350º C. Until the oxygen sensors become operational, the ECM uses presets to determine the injector cycle times.
Control Sensor Same as pre-catalyst sensor.
Diagnostic Sensor Same as post-catalyst sensor.
Downstream Sensor Same as post-catalyst sensor.
ECM or ECU Engine Control Module or Electronic Control Unit; the computer that receives sensor input and controls injector timing.
Emissions–California Vehicles certified for sale in California have an underhood emissions label stating that the vehicle conforms to U.S. EPA regulations and to California regulations applicable to the vehicle model year. Several states in the
northeast, including Maine, Massachusetts, New York, and Vermont have adopted the California standards. Therefore, if there is a difference in oxygen sensor part numbers for California (Calif.) vehicles in this catalog, that difference may also apply to vehicles sold in these northeastern states.
Emissions–Federal Vehicles with “49-State Emissions” certification have an underhood emissions label stating that the vehicle conforms to U.S. EPA regulations applicable to the vehicle model year. The label also states that the vehicle does not meet the emissions requirements for California or, “a state that has adopted California standards.”
Heated Sensor A three or four wire sensor that includes a resistive element to bring the oxygen sensor to its operating temperature much more quickly than can be achieved using the hot exhaust gases alone.
Lambda (-l-) The ratio of the current (instantaneous) Air/Fuel ratio to the ideal (14.7:1) Air/Fuel ratio. If the engine is running rich, l<1. If the engine is running lean, l>1.
Monitor Sensor Same as post-catalyst sensor.
OE-Fit Sensor A sensor that is the original equipment sensor or one that has been engineered to fit multiple applications with minimal adjustment by the installer.
Oxygen Sensor A device that generates a variable voltage or alters a reference voltage depending on the amount of free oxygen in the engine exhaust.
Planar Sensor An oxygen sensor in which the ceramic sensing element with integrated heater is a thin, flat sandwich of zirconia ceramic and printed metallic and insulating layers. These layers are fused into a single piece at very high
temperature in a kiln.
Post-Catalyst Sensor An oxygen sensor mounted in the exhaust stream after the catalytic converter. The output from this sensor is used by the ECM primarily to ensure that the catalytic converter is performing within specifications.
Pre-Catalyst Sensor An oxygen sensor mounted in the exhaust stream before the catalytic converter. The output of this sensor is used by the ECM to vary injector timing.
Reference Air Air inside the oxygen sensor that provides a “normal” oxygen reference, in comparison to the amount of oxygen in the exhaust stream.
Switching Sensor For zirconia types, the voltage output from the sensor changes very rapidly from 800mv to 300mv as the exhaust mixture changes from rich (no free oxygen) to lean (free oxygen). This rapid change occurs at the ideal Air/Fuel mixture of 14.7:1. The opposite occurs as the exhaust mixture changes from lean to rich. For titania types, the resistance across the sensing element changes very rapidly at the ideal Air/Fuel mixture. A voltage is applied by the ECM, and
the voltage drop across the sensing element is measured.
Thimble Sensor An oxygen sensor in which the ceramic sensing element is shaped like a thimble, with a hollow space inside for the reference air and heater. The ceramic can be either zirconia or titania. Nearly all oxygen sensors prior
to 1998 were thimble designs.
Titania Sensor The ceramic sensing element of the oxygen sensor is made of titania dioxide. Resistance across the sensing element changes with the amount of free oxygen in the exhaust gas.
Unheated Sensor A one or two wire oxygen sensor that depends on the temperature of the exhaust gas to reach an operating temperature of 350º C.
Universal Sensor An oxygen sensor that typically includes a connector(s) that allows the sensor to utilize the existing OE wire configuration. Universal sensors can often cover a wide range of applications.
Upstream Sensor Same as pre-catalyst sensor.
Wideband A/F Sensor An oxygen sensor that produces a precise output signal in proportion to the Air/Fuel ratio. This allows the sensor to accurately measure the oxygen content in the exhaust gas.
Zirconia Sensor The ceramic sensing element of the oxygen sensor is made of zirconia dioxide. Voltage generated across the sensing element changes with the amount of free oxygen in the exhaust gas.