On-Board Diagnostics: Basics

The idea of automobiles being as advanced as "robotic cars" from Hollywood fantasy movies sounds like a talk from another dimension altogether. Seeing cars talk and behave in a manner we could understand, seems exciting but unreal. No doubt the technology on our planet is also running at a faster pace, but talking cars? Is still far. However, our technological advancements have enabled us to understand our vehicles much better. They may not talk to us in our languages, but a "diagnostics system" is no less than a language that helps us to understand the condition of our vehicle correctly." An "OBD or On-Board Diagnostics" is where a vehicle can diagnose and report its conditions by displaying various codes.

Vehicle diagnostics are both OFF-board and On-board. Off-board diagnostics, store faults and monitor all the control units to be retrieved later for the technician's help where an On-board comes into the picture when the vehicle is running.  Now understanding the technology behind it, just like CAN Bus, a lower-level protocol system involving the hardware, OBD is a higher-level protocol involving the language. Therefore, any OBD interface device can function as an interface between an OBD port and the vehicle through a computer.

From The Beginning:

Introduced around the late 1970s with a general idea of understanding faults in a vehicle. It found more extensive application in 1980s. It was seen to be used for testing the Engine Control Module (ECM) on the vehicle assembly line. The only function available initially were the "blinking lights". The blinking pattern of "malfunction indicator lights" also known as MIL could be interpreted as "Diagnostic Trouble Codes" (DTC's) to check the engine.  Later, in 1988: The California Air Resources Board (CARB) had made it so that all newer vehicles in California had some basic OBD capability.  However, the data link connector, data protocol, and position were not standardised. A standardised diagnostic connector and set of diagnostic test signals were recommended by The Society of Automotive Engineers (SAE), which were later termed as "OBD-I". After much advancement and up-gradation, OBD-II came into existence, and its specifications were made mandatory for all cars sold in the United States starting the form year 1996.

All significant standards for Diagnostics are mentioned in the table below:

OBD-II & CAN Bus on Internet Protocol Layers
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An OBD connector is a standard 16-pin (DIL) female connector (J1962) located inside the vehicle. The Pin layout can be understood clearly with the image given below. Also, the unspecified pins are subjected to the vehicle manufacturer's discretion.

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Where OBD finds usage?

OBD is an automotive electronic system. It provides vehicle self-diagnosis and reporting capabilities so a user/technician can act upon it. An OBD gives the driver/operator access to subsystem information for monitoring performance and repair needs of the vehicle. Also, self-diagnostic functionality systems are incorporated into the engine control system to alert the vehicle driver/operator about potential problems that can affect the emission performance of an automobile. OBD can efficiently identify faults in

  • Fuel Systems. Number of ignition cycles

  • Engine Misfires. Status of "Check Engine" light

  • Emissions Control Systems. Emission readiness status

  • Vehicle/Speed Idling Controls. Real-time parameters: RPM, speed, pedal position, spark advance, airflow rate, coolant temperature, seat belt, airbags, oxygen sensor test results, and many more related to vehicle body & chassis.

  • Computer Systems. Transmission Systems.

  • Diagnostic trouble codes (DTCs).Vehicle Identification Number (VIN). The number of miles driven with MIL on.

  • One can also get a "snapshot" of parameters when a trouble event has occurred through the "Freeze frame" function.

Reading OBD-II Diagnostics Data

A standard J1979 by SAE defines On-board "Parameter Identification Numbers", commonly knowns as OBD-II PIDs. These are codes used to request data from a vehicle using the diagnostic tool. The engine control unit data can be accessed using OBD-II, which serves as a reliable source of information when any error/fault occurs inside the vehicle. The OBD Protocol standard defines a method for requesting various diagnostic data when troubleshooting inside the vehicle. The primary modes/command structures are as follows:

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Types of DTCs

Here The DTCs (Diagnostic Trouble Codes) are comprised of “one letter and four numbers”. Which fall under a specific given category.

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Influx Module Analyser (MA) software tool is an example of a PC Based OBD Scantool, which can be used to monitor the following

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It also helps to generate reports for different OBD modes (mode 1…10). The tool is preloaded with large number of standard OBD PIDs and DTCs, this means that majority of the OBD data can be immediately retrieved with a single click.

Applications of OBD:

A wide range of tools is available to plug into the OBD connector and access its functions. Ranging from a very simple handheld consumer tool to a very technical and sophisticated one.

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It would not be wrong to say that almost all the latest cars and bikes support OBD2, and most run on CAN (ISO 15765) protocol. We at "influx technology Ltd." are committed to providing modular, easy-to-use OBD data logging solutions. Rebel range of Influx devices can efficiently log OBD data from the vehicle; these devices can also log and transmit telematics information for real-time tracking using the Influx Streamlog add-on service. The data loggers can work as a scan tool when it is used with the Module Analyser software; click here to check out the Influx data logger range, which supports OBD2 data logging.

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