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OBD-II PIDs (On-board diagnostics Parameter IDs) are codes used to request data from a vehicle, used as a diagnostic tool.. SAE standard J1979 defines many OBD-II PIDs. All on-road vehicles and trucks sold in North America are required to support a subset of these codes, primarily for state mandated emissions inspections.
The "Drive-cycle" basically is the representative of the road. Drive cycles are used to reduce the expense of on road tests, time of test and fatigue of the test engineer. The whole idea is to bring the road to the test lab (a chassis dynamo-meter) or to the computer simulation. Two kinds of drive cycle can be made.
OBD-II is an improvement over OBD-I in both capability and standardization. The OBD-II standard specifies the type of diagnostic connector and its pinout, the electrical signalling protocols available, and the messaging format. It also provides a candidate list of vehicle parameters to monitor along with how to encode the data for each.
Transport-layer services include the transmission of multi-CAN-frame messages based on the ISO 15765-2 multi-frame messaging scheme. It was developed and is used primarily by General Motors for in-vehicle communication and diagnostics. [3] GM's Tech2 uses the CANdi (Controller Area Network diagnostic interface) adapter to communicate over GMLAN.
It is also known as FTP-72 or LA-4, and it is also used in Sweden as the A10 or CVS (Constant Volume Sampler) cycle and in Australia as the ADR 27 (Australian Design Rules) cycle. [4] The cycle simulates an urban route of 7.5 mi (12.07 km) with frequent stops. The maximum speed is 56.7 mph (91.2 km/h) and the average speed is 19.6 mph (31.5 km/h).
To ensure high quality in the Computer Command Control system, it will be given a final check at the end of the assembly line. Here the completely assembled vehicle will be tested by connecting the computer to a test computer. This will significantly improve GM's ability to catch anything wrong with the system or the car's engine." [1] [2] [3]
When the computer detected a fault, it illuminated the MIL. Up until OBDII, on most cars the MIL could output codes. When two pins on the ALDL are jumped, the light would flash the codes, for instance (blink) (pause) (blink) (blink) for code 12. Some manufacturers, such as Honda, retained this feature even after OBDII.
The ELM327 is a programmed microcontroller produced for translating the on-board diagnostics (OBD) interface found in most modern cars. The ELM327 command protocol is one of the most popular PC-to-OBD interface standards and is also implemented by other vendors.