Kits used in Pakistan In Pakistan different manufacturers use different OBD kits for diagnosis and service Currently the leading Automobile brands are Toyota Honda Land Rover The kits used by their service centers are Manufacturer specific Different kits comparisons and there description is given in the Table Name of Kit Type IDS SDD Specific for Land Rover Ford Jaguar Toyota IT Specific for Toyota Honda IM Specific for Honda Launch Generic Carman Generic BACKGROUND The first incarnation of On Board Diagnostics specification was developed by Society Of Automobile Engineers was known as OBD I OBD was the first standard of its kind however it was not mandatory Its main purpose was to encourage manufacturers to create more efficient engines thus leading to reduced emissions and better fuel economy However the first OBD standard was not perfect it had a lot of problems primarily the following The data link connector DLC in which scan tools would connect to in order to interface with the ECU was not standardized This prevented generic scan tools being manufactured that would work with all vehicles Each vehicle manufacturer had its own unique set of diagnostic codes for identifying errors in the engine management system
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This was another major problem for creating generic diagnostic hardware The type of information stored on the vehicle s ECU was different from manufacturer to manufacturer These problems led to the development of a newer standard that would combat these issues and provide better standardization OBD II was developed in 1996 It supported better standardization to the areas in which the first version of OBD failed A standard physical data link connector was made mandatory by the specification The connector is defined by the J1962 standard that the SAE specified This new standard DLC allowed diagnostic hardware manufacturers to produce generic hardware that worked on any modern vehicle Diagnostic trouble codes DTCs were made standard however manufacturers were still allowed to include more detailed proprietary ones SYSTEM HARDWARE AND SOFTWARE DESIGN An indigenously developed OBD kit uses the ELM327 to communicate with the vehicles It is certainly possible to communicate with the ECU of the vehicle using a microcontroller but that bounds the user to one specific protocol and that would mean a different kit for different vehicle so a generic kit using elm327 which can shift to what so ever required protocol is
This developed OBD kit will be compatible with two signaling protocols used commonly in Pakistan ISO protocol and CAN protocol Earlier two separate kits were used for these different protocol compatible vehicles Hardware components The major hardware components for the ISO and CAN compatible kits were ELM327 the MCP2551 transceiver hardware 2N3904 2N3906 and the laptop The need of this project is to design a significant hardware component so it is decided to develop a single kit that is compatible with both the protocols This device would be completely battery free and powered completely through the OBD II port which draws 12V from the vehicle's electrical system This would be in consistent with the goal which was to make an easy to use OBD II reader that is typically used in garages Development of the Software The software should be developed to work in union with the ELM327 in order to provide useful functionality to mechanics and technicians C and GUI software design must be incorporated which is easy to use These are some of the functionalities which must be shown in this software Parameter IDs PIDs Diagnostic Trouble Codes Pilot Correction Learning WORKING OF KIT The Signaling Protocols There are five signaling protocols that are permitted with the OBD II interface Most vehicles implement only one of the protocols It is often possible to deduce the protocol used based on which pins are present on the J1962 connector SAE J1850 PWM pulse width modulation SAE J1850 VPW variable pulse width ISO 9141 2 ISO 14230 KWP2000 Keyword Protocol 2000 ISO 15765 CAN Fig 2 Protocols and the Diagnostic Jack OBD II Modes and Parameter IDs PIDs A parameter ID PID is a unique code or command that OBD assigns to a specific data request type
So in order to communicate with an ECU using OBD II you must first send the appropriate PID for the type of information you want and the ECU will then respond with a sequence of bytes In the original J1979 specification document of the SAE it lists 9 diagnostic test modes They are as follows Request Current Powertrain Diagnostic Data Mode Request powertrain freeze frame data Request emission related diagnostic trouble codes Clear reset emission related diagnostic information Request oxygen sensor monitoring test results Request on board monitoring test results for specific monitored systems Request emission related diagnostic trouble codes detected during Current or last completed driving cycle Request control of on board system test or component Request vehicle information How data is sent on the ECU bus Since OBD II works on a bus based technology the identification of source and destination need to be accounted for Without it the scan tool would never be able to locate the message that is destined for it The message mode and PID is encapsulated in a header and footer
The header format includes 3 fields a priority field a receiver or target address TA and sender or source address SA OBD II s messaging works on a priority based scheme Some messages within an engine s management system are more critical than others Interpreting OBD II Responses The data returned from the ECU is in the form of a series of bytes The response can either be bit encoded or simply value based bytes however generally a formula must be applied to the bytes in order to decode the actual response in a human understandable format There is no generic way of working with returned data All PIDs have their own way of dealing with the returned data
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