1 Freeze Frame Data
When the OBD trouble codes related to Automobile engine exhaust emissions appears, OBD-II not only set one OBD trouble codes, but also can record the relevant system operating parameters while the OBD trouble codes appear. The series data are called froze frame data: it includes Engine RPM, vehicle speed, air flow, engine load, fuel pressure, fuel modifier, engine coolant temperature, manifold pressure, and open-loop or closed-loop status etc.We can use OBD-II Trouble diagnostic program to freeze-frame testing of the vehicles which follows OBD-II Standard.
2  Readiness Tests
OBD-II system monitors multi-regions of the engine operating system, three regions of them are continuously monitored while other regions just will be monitored in certain conditions. Activating these discontinuous monitoring device need the vehicles under the work conditions of travelling the certain distance and time at a certain speed or special engine temperature、acceleration and deceleration alternately recycling etc to be monitored, this is called Readiness Tests Not all of vehicles are applicable to this test. For those vehicles in OBD-II standard can be conducted the Readiness Test with OBD-II diagnostic fault diagnosis program by OBD II code reader.

Data stream test function
Through establishing the communication between automobile fault diagnostic computer and automobile computer, get shared data out from RAM of the vehicle computer microcomputer to analyze vehicle trouble, so the data stream testing function is an important function of auto fault diagnostic computer. Data stream is divided into static data (KOEO) and dynamic data (KOER).

All vehicle that adopting microcomputer fault self-diagnosis system can using computer tester to readout the data stream that output by vehicle various electronic control unit microcomputer through diagnostic socket and reflects the electronic control unit controls system working conditions. Maintenance personnel can judge whether the electronic control devices work properly by making numerical analysis of various parameters of data stream, providing the basis for finding cause of the malfunction.

Parameters in data stream has two forms, numerical parameters and status parameters. The numerical parameters is the parameters that has certain units and a certain change range, which usually reflects the operating voltage, pressure, temperature, time, speed, etc. of each part in the work of the electronic control unit; state parameter is those who have only two states, such as on or off, closed or disconnected, high or low, yes or no, etc., it usually signify the working condition of the components of electronic control devices such as switches and solenoid valve.

In conducting numerical analysis, you must first distinguish between the various parameters are input signal transmitted to microcomputer from the sensor of electronic control device or the output command sent to the electronic control unit actuator by microcomputer. Input signal parameters can be state parameters, so can be numeric parameters. Most of the output command parameters are state parameters, a small part is numerical parameters. Data stream parameters can be classified according to various systems of vehicle and engine. Parameters of parameters of different types or different system have different analysis methods. During electronic control unit failure diagnosis parameters of several different types or different systems are needed to go through comprehensive contrast analysis. Different brands and different models of vehicles, the name and content of their electronic control device data stream parameters are not exactly the same.
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