Octane Rating
A unit of measurement on a scale intended to indicate the tendency of a fuel to detonate or knock based on the percentage of isooctane in the fuel. The higher the rating, the higher the percentage of isooctane and therefore the greater the resistance to detonation offered by the fuel.

Off-Highway Vehicle
Vehicle intended for operation on unmade surfaces or rough terrain (i.e. for construction or agriculture).

Ohm
After Georg Simon Ohm, German (1787-1854). The ohm is a unit of electricalresistance.

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.

Open End Lease
A lease in which the lessor is not responsible for the value of a vehicle when the lease is done. Under this arrangement the lessee is responsible for the difference between the current actual market value at the end of the lease and the residual value. Also known as a "finance" lease.

Overdrive
A transmission in which the highest gear ratio is less than a one-to-one ratio. This means the drive shaft turns faster than the engine crankshaft. The overdrive feature saves fuel and, because the engine runs slower, engine wear and noise are reduced.

Overhead Cam
The type of valve train arrangement in which the engine's camshaft is mounted above the cylinder head(s). When the camshaft is placed close to the valves, the valve train components can be stiffer and lighter, allowing the valves to open and close more rapidly and the engine to run at a higher RPM. In a single overhead cam (SOHC) layout, one camshaft actuates all of the valves in a cylinder head. In a dual overhead camshaft (DOHC) layout, one camshaft actuates the intake valves, and one camshaft operates the exhaust valves.

Overhead Valve Engine (OHV)
An engine with both intake and exhaust valves placed directly over the piston. In this design, the camshaft is located in the block, and the valves are actuated by pushrods and rocker arms.

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