Distributorless Ignition System (DIS): An electronic ignition system which does not have a conventional rotating distributor. It employs multi-spark ignition coils or one ignition coil for each spark plug.

Distributor: A mechanically driven device on an engine which is responsible for electrically firing the spark plugs at a pre-determined point of the piston stroke and in the desired firing order.

Displacement: The volume of the cylinder between the top dead centre and the bottom dead centre positions of the piston.

Direct injection: A fuel injection system for diesel engines, wherein the fuel is injected directly into the combustion chamber, onto the top of the piston.

Direct ignition: An ignition systems without any distributor, wherein the spark distribution is controlled by the computer.

Diode: It is a basic electronic component formed by combining a N-type and a P-type semi-conductor back-to-back. Diodes are commonly used as rectifiers.

Digital fuel injection (DFI): A system, identical to earlier electronic fuel injection system, but with digital microprocessors. In this analog inputs from various engine sensors are converted to digital signals before processing. The system is self-diagnosing and self-monitoring.

Diesel Particulate Matter (DPM): Sub-micron size particles found in the exhaust of a diesel engine. DPM consists of both solid and liquid particles and is usually classified into three fractions. viz., inorganic carbon (Soot), organic fraction and sulphate fraction.

Diesel Particulate Filter (DPF): A filter which removes small particles from exhaust of a diesel engine.

Dieseling: A condition in which an S.I. engine continues to run for some time after the ignition is turned off; caused by the hot spots in the combustion chamber.

Diesel index: Diesel index is defined as: Diesel index = Aniline point (°F) x API gravity (deg)/100

Diagnostic socket: A socket on the vehicle, usually located in the engine compartment, which is part of the onboard electronic sensor system.

Diagnostics: Process of identifying the cause or nature of a condition or problem to determine the appropriate corrective action to take for repairing an automotive system.

Diagnostic code: Code number obtained by accessing the diagnostic mode of the engine management computer. This code can be used to determine the area in the system where a malfunction may be there.

Detonation sensor: A sensor, which is often piezoelectric, mounted near the cylinders which can detect engine knocking or frequencies of detonation so as to send a message to the ECU to retard the ignition timing to prevent damage to the engine.