OBD 2 diagnostic system

What is the difference between OBD 2 and OBD 1? With OBD 1 each manufacturer used their own unique codes and definitions for identifying failures in the computerized engine management system.

This made it difficult on auto mechanics, servicing multiple vehicle brands. With OBD2 common codes and definitions were developed to identify all basic emissions related failures OBD 2 trouble codes consist of one alpha character followed by four digits.

The alpha character indicates the area of the vehicle were the failure occurred. This includes B for body, C for chassis, P for power train, and U for network.

The network would be considered a manufacturer specific code used only on a specific model or brand. The body would include the airbag system or SRS codes. The chassis would include ABS codes. The power train includes the transmission and engine codes

The first digit of the diagnostic trouble code denotes the origin of the code. Check engine light codes authored by the Society of automotive engineers or, SAE are identified by zero.

Generic OBD 2 codes

The second digit in the diagnostic trouble code identifies the system, where the malfunction is occurring. The last two digits correspond to a specific code definition.

OBD 1 and OBD 2 are similar in that both systems checked sensor and actuator circuits for opens shorts and out of range values.

However, the failure limits for OBD one are far more forgiving, since a circuit or component must fail completely before the check engine light is illuminated or a diagnostic trouble code is stored.

In contrast obd2 use a series of monitors or diagnostic tests that conduct performance evaluations on an emission components.

OBD 2 sensors and subsystems

This capability makes it possible for emissions related problems to be identified and corrected before excessive pollutants are discharged in the atmosphere via the tailpipe.

OBD2 monitors, comprehensive components, misfire detection, fuel control, exhaust gas recirculation or ERG functions, catalyst efficiency, oxygen sensors, O2 sensor heating circuits, evaporative commissions system, and even AC refrigerant levels.

OBD two monitors are defined as being continuous or non-continuous. As the name indicates continuous monitors run all the time. These monitors include comprehensive components, misfire detection and fuel control.

The remaining monitors or noncontinuous, since they do not run until certain criteria has been met. Enable criteria include specific driving an engine operating conditions that must occur before the PCM will execute the monitor.

Consequently, if the vehicle is driven in a way that does not satisfy the enable criteria for a particular non-continuous monitor that monitor will not run and no codes will be set even if a circuit malfunction exists.

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