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 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. This includes all discriminating crash sensors, clock spring and the air bag deployment module.

The chassis would include ABS codes as well as suspension codes if the vehicle is equipped with active suspension.

The power train includes the transmission and engine codes. This is by far the most common system to set computer trouble 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

These codes are known as generic diagnostic trouble codes since they are the same for every vehicle. The number one indicates manufacturer specific codes.

These diagnostic trouble codes are part of the manufacturers influenced diagnostic software and varying between vehicle manufacturers.

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. If a monitored circuit fails to meet minimum performance standards even though the circuit may still be operating.

OBD 2 sensors and subsystems

The power train control module will illuminate the check engine light and store a diagnostic trouble code to aid in the mechanics diagnosis.

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.

As well as all O2 sensor heating circuits, evaporation emissions system (fuel vapor), and even AC refrigerant levels on some models that have climate control technology.

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

Enable criteria will include specific driving and engine operating conditions that must occur before the PCM (Powertrain control module) will execute or activate the MIL (maintenance indicator light).

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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