What is OBD and OBD II Software Stack?

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What is OBD and OBD II Software Stack?


On-Board Diagnostics (OBD), as the name suggests, refers to the in-vehicle system that detects and reports the status of vehicle health. With the help of an OBD port (fitted in a vehicle) and OBD connector, the repair technician/after-sales service provider gets access to critical vehicle parameters like vehicle speed, engine data, emission data and more in the form of Diagnostic Trouble Codes (DTC)

What is On-Board Diagnostics (OBD)?


What is OBD II software stack?

• In order to facilitate a standardized method of diagnosis and correction of vehicle emission related malfunctions across the geographies, International Standards Organization (ISO) introduced ISO 15031 standard for automotive industry.

• ISO 15031 is a standard for Communication between vehicle (OBD port/connecter, defined by SAE J1962) and external equipment (Diagnostic Tester) for emissions-related diagnostics

• OBD II stack is a set of software specifications or services implemented based on ISO 15031 standard. This OBD II software stack is best suited for passenger car and light commercial vehicle applications


OBD II stack implemented over five signaling protocols as shown below

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Vehicle communication can be broadly classified into two:

1) In-vehicle networking: This refers to exchange of data between various automotive electronic control units (ECU) which are part of the vehicle network.

Automotive Protocols like CAN (Controller Area Network), LIN (Local Interconnect Network), Flex Ray, MOST (Media Oriented Systems Transport) are defined for in-vehicle network communication.

Usually this is a broadcast network and one can add listen-only nodes easily.

Types of in-vehicle communications


2) Vehicle Diagnostics/External communication: Vehicle Diagnostics communication is used for diagnosis and repair of vehicle sub-systems or ECU.

This type of communication is useful for monitoring and reporting of system malfunction monitoring and vehicle parameters. An external tool may be used to re-configure and re-flash the ECU to rectify the malfunction.

Vehicle Diagnostics is a query-response communication. The external tool asks for a particular information (diagnostic request) and the ECU (the control unit to which the query is directed) responds with the answer (diagnostic response)

For diagnostic communication, the physical medium (also known as the signaling protocol) is same as the medium used for in-vehicle communication – CAN, LIN, Flex ray, MOST.


• OBD II qualifies as a protocol for vehicle diagnostics communication (query-response communication).

• OBD II is a part of emission legislation. Hence it follows the CARB (California Air Resources Board) initiated protocol mandates. OBD II protocol monitors parameters in emission relevant ECUs as per the guidelines of CARB.

• OBD II also follows CARB guidelines for data storage and data accessibility to be provided to the external scan tools.

• Diagnostic protocols like UDS and KWP2000 support re-configuration and re-flashing of ECU (writing to EEPROM and Flash), but OBD II supports only read access.

OBD II protocol and Vehicle Diagnostics Communication:


ISO 15031 mandate that the following modes should be supported:


OBD Challenges/Limitations

• Data available over OBD port (OBD connector) is related to powertrain and emission ECUs’.

Hence access to body control data like seat belt status, airbag status and more is not available

• Data is available only in query-response mechanism.

• OEMs have option to define proprietary DTCs (Diagnostic Trouble Codes) and not make it

available in the public domain. It is also observed that some vehicle parameters are not

supported in certain vehicle models. These can lead to compatibility issues

• OBD supports only read-access to emission relevant data (vehicle parameters, DTCs). There is no

support for write-access to data for reprogramming or test sensors/actuators. Hence it is not

easy to monitor and rectify malfunction related to vehicle functionality (for example engine

immobilizer) using OBD communication.


• OBD II software stack, designed and developed by our expert automotive developers, is a set of embedded software services implemented in compliance with ISO 15031 standards for automotive.

• To know more about our OBD II stack design and development services mail to [email protected]

http://www.embitel.com/obd-ii-stack-services

http://www.embitel.com/obd-ii-stack-services

mailto:[email protected]