O2 SENSOR
Device that converts oxygen content present in the exhaust stream to a voltage signal, usually between 1.0-1.5 volts. This voltage signal is used by the ECM to help determine mixture. O2 sensors need to reach operating temperature before they start to operate, and do wear out over time. Fiats used O2 sensors on the fuel-injected models, see your service manual for test procedures.

Octane
A numeric rating of gasoline’s resistance to detonation(premature ignition). The higher the octane number, the less chance of detonation. High octane (above 91) is usually worthwhile only if the manufacturer specifically recommends it. Octane is actually a hydrocarbon(C8H18).

OCTANE RATING
The octane rating defines resistance to preigniton in fuels for spark-ignition engines. Higher octane ratings indicate a greater resistance to knock Two different procedures are in international use for defining octane ratings.

Oilhead R-bikes
Oilheads are BMW's answer to consumer complains when they announced they'd be killing off the R-bike line in the late eighties or early nineties. They realized they'd alienate a big chunk of their customers, but they didn't want to keep flogging the poor Airheads, which were no longer even vaguely modern bikes. The result was the Oilhead, which is an Airhead engine warped 20 years into the future.

The term Oilhead comes from the fact that this engine type is oil cooled, and has oil flowing up into the heads. These engines really are drastically redesigned Airheads, with the basic layout being the real resemblance to the Airhead. Fuel injection is used instead of carbeuration. Engine control computers are normal on these bikes. New materials were used in the construction of the engine. The bike which goes around the engine is also different, with a greatly upgraded suspension, gearbox, clutch, appearance, etc.

On Board Diagnostics
(OBD) a unit that monitors the Electric Control Unit and system responses for errors during normal vehicle operations. When the vehicle is serviced, this information on the errors can be down loaded and displayed to the service personnel which will facilitate the trouble shooting process.

OPERATING DATA ACQUISITION
Sensors monitor all essential operating data to furnish instantaneous information on current engine operating conditions. This information is transmitted to the ECU in the form of electric signals, which are converted to digital form and processed for use in controlling the various final-control elements.

OPERATING DATA PROCESSING
The ECU processes the engine operating data recieved from the sensors. From this data, it uses the programmed ECU functions to generate the triggering signals for the fuel injector, the throttle valve actuator, and the canister-purge valve.

OVERRUN FUEL CUTOFF
Overrun fuel cutoff is the complete interruption of the supply of fuel to the engine during deceleration in order to reduce the fuel consumption and exhaust gas emission when driving downhill and decelerating. Since no fuel is burned, there are no emissions.

OXIDATION CATALYTIC CONVERTER
The oxidation catalytic converter operates with excess air, and inploys oxidation, i.e. combustion, to convert hydrocarbons and carbon monoxide into water vapor and carbon dioxide. Oxidation catalytic converters provide virtually no reduction in nitrous oxides. With fuel-injection engines, the oxygen required for oxidation is usually obtained feom lean induction mixtures. Carburetor engines rely on engine-driven centrifugal pumps or self-priming air valves to inject "secondary air" into the exhaust stream before it reaches the catalytic converter.