O

OHM - A unit of electrical resistance opposing current flow. Resistance varies in different materials and varies with temperature.

OHMMETER:

OHMMETER - An instrument that measures electrical resistance of a conductor in units called ohms.
OHM'S LAW - A law of electricity which states the relationship between voltage, current and resistance. It takes an electromotive force of one volt to force one ampere of current through one ohm of resistance. Equation - volts = amperes x ohms (E = I x R)


ON DEMAND TEST - In Self-Test, the Key On/Engine Off and Engine Running positions, which are technician initiated, are run from a program within the processor.


OPEN CIRCUIT - An electrical circuit that because of break or because a switch has failed to close is not complete. See also "short circuit."


OPEN LOOP - A system that does not feed back its output to its input.


OPERATIONAL AMPLIFIER - A device with two inputs and one output having a very high voltage gain.


OPTIC SENSOR - A device that produces a voltage signal by using a light source, a light sensitive material and a slotted wheel between the two.


OR GATE - A type of logic circuit that if either input is YES, the output is YES.


OSCILLATION - A rapid back-and-forth movement.


OSCILLOSCOPE - Instrument that converts voltage and frequency readings into traces on a cathrode ray tube.


OUTPUT - Decisions or commands issued by a microcomputer to output devices to allow displays and actuators to function.


OUTPUT CONTROL - Circuits inside of the ECA that are used to turn external devices on and off.
OUTPUT CYCLING CHECK (OCC) - A position of the end of the Key On/Engine Off test that enables energizing and de-energizing the auxiliary output on demand.


OUTPUT DRIVER - A transistor in the output control area of the processor that is used to turn various actuators on and off.


OUTPUT STATE CHECK - A test performed in the Key On/Engine Off mode after the continuous codes have been sent which forces the processor to activate some actuators for additional diagnostics.


OVERCHARGING - Continuing to charge a battery after it has a full charge; can damage the battery.