OBD II
On-Board Diagnosis - A (self-diagnosis) mechanism is provided by the DME III or DDE engine management system. Its purpose is to permit malfunctions tube identified before more serious damage results. Defects which occur suddenly, or values which go beyond the specified tolerance limits, are stored electronically and can be displayed and evaluated later on the screen of a diagnostic testing unit in the workshop. Troubleshooting then becomes much more straightforward and costs are reduced.
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Octane Ratings
The octane rating of petrol (gasoline) tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Lower-octane petrol can handle the least amount of compression before igniting.
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Odometer
An instrument for measuring and registering the miles and tenths of miles driven. Some cars also have an additional trip odometer, which can be reset to zero for conveniently measuring the miles driven during trips or between fuel fill-ups. |
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OFFSET
The distance between the vertical center of the wheel and the mounting surface at the lugs. Offset is positive if the center is outside the lug circle; negative offset puts the center line inside the lug circle. |
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OHC
OverHead Cam - A type of engine design in which the camshaft is located directly above the combustion chamber in the cylinder head instead of in the engine block.
SOHC (Single OverHead Cam) engines have one overhead camshaft operating all the valves.
DOHC (Double OverHead Cam) engines have two overhead camshafts operating all the valves. |
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OHV
OverHead Valve - an engine design where the camshaft is installed inside the engine block and valves are operated through lifters, pushrods (Reason why OHV engine are also known as "Pushrod" engine(s)) and rocker arms .
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Oil Pump
An engine-driven pump that delivers oil to all the moving engine parts. |
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On-board Computer
Gives the driver a fast, easy-to-understand overview of key trip information - and provides timely warning about hazardous driving conditions. The amount of information given on the On-board computer varies from manufacturers and choices made by the driver.
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On-board Diagnosis
One of the functions of Digital Motor Electronics (DME), which monitors and manages all core functions of a DME equipped vehicle. The on-board diagnosis system instantly recognizes any deviation from normal component function and sends an alert message to the cockpit. The driver is immediately informed about any issues with the engine, and can take action to ensure that no further damage is caused.
All error messages (e.g. variations in emissions) are logged and can be used to find the solution. |
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OPDS
Occupant Position Detection System - measures occupant height and seat position to determine if the passenger seat-back airbag should be disabled. This seat-back airbag has an indicator lamp on the instrument cluster that illuminates when an occupant is detected in an unsafe position or if their backs are not pressed firmly against the seat back.
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Overdrive
In the five-speed manual transmission, the fifth gear is built into the gearbox as a true overdrive. This means the driveshaft turns faster than the engine crankshaft. The overdrive feature saves fuel, and because the engine runs slower, engine wear and noise are reduced. |
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Oxygen Sensor
Used with a feedback system to sense the presence of oxygen in the exhaust gas and signal the computer which can use the voltage signal to determine engine operating efficiency and adjust the air/fuel ratio. |
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