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OBD-II On-Board Diagnostics

ECU	Eengine Control Unit: controls a series of actuators on an internal combustion engine to ensure optimal engine performance.
DTC	Diagnostic Trouble Code: 4-digits, preceded by a letter: P for engine and transmission (powertrain), B for body, C for chassis, and U for network,
PID	On-board diagnostics Parameter IDs, codes used to request data from a vehicle.
Service	OBD-II standard (SAE J1979) defines several services (or modes) used to communicate with the ECU. There is a service to request PIDs data, a service to clear DTC, etc.
MIL/CEL	Malfunction Indicator Lamp/Check Engine Light, typically has amber color. When the MIL is lit, the engine control unit stores a fault code DTC related to the malfunction.
Freeze Frame	When the check engine light turn on, the ECU determines the error based on several engine operating conditions and stores it in what’s called a OBDII freeze frame. The data stored in Freeze Frame is usually recorded when a system fails the first time for two consecutive trip faults. Freeze Frame data will only be overwritten by a different fault with a higher priority.
Closed loop mode
Misfire

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