On Board DiagnosticsOBD

Rebecca Doebler, James Carl, Joe RomeoEECS 498

What we will learn today

• What is OBD?

• History of OBD

• DTC (Diagnostic Trouble Codes)

• Progression of the OBD protocol over time

• Low level implementation of OBD II protocol

• High level overview of OBD II protocol

• OBD Products

OBD (On Board Diagnostics)

• What is OBD?

• History of OBD

• DTC (Diagnostic Trouble Codes)

• Progression of the OBD protocol over time

• Low level implementation of OBD II protocol

• High level overview of OBD II protocol

• OBD Products

What is OBD?

• On-board diagnostics

• An automotive term referring to a vehicle's self-diagnostic and reporting capabilities

• Tools with OBD allow mechanics and vehicle manufacturers to connect to the vehicle's on-board computers and diagnose any potential failures in the engine, as well as retrieve information such as rpm, horse-power, etc.

Source: 1

Why is OBD important?

• OBD is required by the Clean Air Acts Amendments of 1990

• Provides a simple, quick and efficient way for repair technicians to pinpoint problems by retrieving automobile diagnostics

• Plays an important role in vehicle inspections and maintenance programs for state agencies

• Provides an early warning system to vehicle owners through the check engine light

OBD (On Board Diagnostics)

• What is OBD?

• History of OBD

• DTC (Diagnostic Trouble Codes)

• Progression of the OBD protocol over time

• Low level implementation of OBD II protocol

• High level overview of OBD II protocol

• OBD Products

Brief History of OBD

• 1969: First on-board computer system with scanning capability

• 1980: GM implements ALDL to test ECM(engine control module). ALDL was the first standardized on board diagnostic protocol

• 1991: California required all cars from 1991 on to have OBD capabilities(refers to OBD I)

• 1994: California wanted a way to do statewide emissions testing. This was the start of OBD II

• 1996: OBD II is mandatory for all of United States

• 2004: European Union makes OBD II a requirement for all cars sold in Europe

see http://en.wikipedia.org/wiki/On-board_diagnostics for more information about OBD history

OBD (On Board Diagnostics)

• What is OBD?

• History of OBD

• DTC (Diagnostic Trouble Codes)

• Progression of the OBD protocol over time

• Low level implementation of OBD II protocol

• High level overview of OBD II protocol

• OBD Products

Why is my check engine light on?

• We use DTCs or Diagnostic Trouble Codes to determine the problem

• Example: o An electronic control module uses an oxygen sensor

to monitor exhaust gas for being rich or leano If the computer feels like the conditions are right for

the sensor to be malfunctioning, it will set a DTC and the check engine light will illuminate

Diagnostic Trouble Codes (DTCs)

• Older OBD protocols have fewer DTCs and are not standardized

• Newer OBD protocols have many more DTCso Latest OBD protocol has a five digit DTC

First Character - System

The first character identifies identifies the system related to the trouble code.

• P = Powertrain• B = Body• C = Chassis• U = Undefined

DTCs (cont)Second Digit - Code TypeThe second digit identifies whether the code is a generic code (same on all OBD-II equpped

vehicles), or a manufacturer specific code.

• 0 = Generic (this is the digit zero -- not the letter "O")

• 1 = Enhanced (manufacturer specific)

Third Digit - Sub-SystemThe third digit denotes the type of sub-system that pertains to the code

• 1 = Emission Management (Fuel or Air)

• 2 = Injector Circuit (Fuel or Air)

• 3 = Ignition or Misfire

• 4 = Emission Control

• 5 = Vehicle Speed & Idle Control

• 6 = Computer & Output Circuit

• 7 = Transmission

• 8 = Transmission

• 9 = SAE Reserved

• 0 = SAE Reserved

Fourth and Fifth DigitsThese digits, along with the others, are variable, and relate to a particular problem. For example,a

P0171 code means P0171 - System Too Lean (Bank 1).

OBD (On Board Diagnostics)

• What is OBD?

• History of OBD

• DTC (Diagnostic Trouble Codes)

• Progression of the OBD protocol over time

• Low level implementation of OBD II protocol

• High level overview of OBD II protocol

• OBD Products

Standard Interfaces - ALDL

• ALDL - Assembly line diagnostic linko Developed by GM prior to OBD I o System was only vaguely standardized o Specifics for communication link varied based on

model

• Diagnostic Connector:o At least four different connectors used with ALDLo 12-pin connector was most widely used for GM o Generally only three pins were used for basic ALDL-

ground, battery-voltage and a single line for datao Most other pins used for additional diagnostic

information and control interfaces

Standard Interfaces - ALDL (cont)

• Example 12-pin connector:

• Data Stream: o Unidirectional data (earlier versions)o Serially transmitted at a baud rate of 160 using

PWMo Bidirectional data (later versions) at a baud rate of

8192 o Request-driven

Standard Interfaces - OBD I

• Introduced in 1981

• No standardization among this generation of technology

• Manufacturer-specific OBD I systems required a variety of diagnostic software and hardware.

• OBD I vehicles were built through model year 1995

Standard Interfaces - OBD 1.5

• Partial implementation of OBD II

• Same pinout as OBD II

• Fewer fault codes

Quick Recap

• Discussed what OBD is, and why it's important

• Brief overview of the history of OBD and the progression of OBD protocol over time

• Talked about DTC codes and how we can use them to diagnose check engine light issues

OBD (On Board Diagnostics)

• What is OBD?

• History of OBD

• DTC (Diagnostic Trouble Codes)

• Progression of the OBD protocol over time

• Low level implementation of OBD II protocol

• High level overview of OBD II protocol

• OBD Products

Connector

http://www.automation-drive.com/obd-connector http://www.carplugs.com/Product_view_Cables_2.html

OBD-II Signal Protocols

• Five Signal Protocolso SAE J1850 - Pins 2 and 10

PWM - Ford VPW - GM

o ISO 9141/14230 - Pins 7 and 15 Serial communication Used by Chrysler and Europeans

o ISO 15765 - Pin 6 and 14 CAN communication Used by all since 2008

SAE J1850 PWM/VPW

• PWM o 41.6 Kb/s using pin 2 as Bus +, 10 Bus -o Developed by Fordo Differential Voltage Signalingo High is +5V differentialo 10 byte message

• VPWo 10.4 Kb/s using just pin 2 as Bus +o Developed by GMo Single wire voltage signalingo ~7V High, <3.5V Lowo 10 byte message

PWM Signaling

http://shieldedpair.net/BAE5030/Lectures/J1850%20Introduction.pdf

VPW Signaling

http://shieldedpair.net/BAE5030/Lectures/J1850%20Introduction.pdf

Message Frame - PWM/VPW

• SOF - High signal for 200us

• Header - 1 or 3 bytes

o Priority 3 bits, 000 low priority, 111 high priority

o Header type, 0 means three byte header, 1 means single byte

o In frame response, 0 means IFR required

o Address mode, functional address(0), physical(1)

o Message type, two bits

• Data

• CRC - Cyclic redundancy check, a type of error checking

• NB - Normalized Bit

http://shieldedpair.net/BAE5030/Lectures/J1850%20Introduction.pdf

CRC - Cyclic Redundancy Check

• Error Checking

• 1 byte checksum

• Sequentially calculated

• Implemented with XOR gates

• Generator Polynomial - 0x1D

ISO 9141/ISO 14230 KWP2000

• Serial-like protocol

• Used by Chrysler and European Companies

• 10.4 Kb/s

• 0V low, 12V high

• ISO 9141: Capable of 12 byte message

• KWP2000: 255 byte message

ISO 15765 CAN

• 1 Mbit/s

• Must be implemented on all cars built after 2008

ISO 15765 CAN Message Frame

OBD (On Board Diagnostics)

• What is OBD?

• History of OBD

• DTC (Diagnostic Trouble Codes)

• Progression of the OBD protocol over time

• Low level implementation of OBD II protocol

• High level overview of OBD II protocol

• OBD Products

High Level Overview of OBD II

• Send request over CAN bus

• Request is a 1 to 2 byte messageo message is between 1 and 2 bytes long, consisting

of a mode, and followed by a PID when necessary

• OBD II responds with a messageo size varies depending on request

see http://en.wikipedia.org/wiki/OBD-II_PIDs for information on different modes and PIDs

Modes

Mode (hex) Meaning

0x01 Show current data

0x02 Show freeze frame data

0x03 Show stored Diagnostic Trouble Codes

0x04 Clear Diagnostic Trouble Codes and stored values

0x05 Test results, oxygen sensor monitoring

0x06 Test results, other component/system monitoring

0x07 Show pending Diagnostic Trouble Codes

0x08 Control operation of on-board component/system

0x09 Request vehicle information

0x0A Permanent DTC's (Cleared DTC's)

see http://en.wikipedia.org/wiki/OBD-II_PIDs for information on different modes and PIDs

Example 1

• Send request over CAN buso in this case, we'll send mode 0x03 (show stored

DTC's)o doesn't require a PID

• OBD II responds with all of the stored DTC's

Example 2

• Send request over CAN buso in this case, we'll send mode 0x01 followed by PID

0x05o remember, 0x01 is the mode for current data, and

PID 0x05 specifies engine coolant temperature

• OBD II responds with a 1 byte messageo temperature readings can be between -40 and 215o so to get our temperature reading, we do (received

message - 40)

OBD (On Board Diagnostics)

• What is OBD?

• History of OBD

• DTC(Diagnostic Trouble Codes)

• Progression of the OBD protocol over time

• Low level implementation of OBD II protocol

• High level overview of OBD II protocol

• OBD Products

OBD Products

• Hand-held scan tools

• Mobile device based tools and analysis

• PC based scan tools and analysis

OBD Products

• Hand-held scan tools

• Mobile device based tools and analysis

• PC based scan tools and analysis

Hand-held Scan Tools

• Costs as little as $15 and

as much as $500

• Cheaper models support less protocols, which means less cars

• Cheaper models also have less features

Cheap Hand-held Scanner U380 Engine Check OBD-II Scanner

• Very cheap ($20.88 + shipping on Amazon)

• Doesn't support the CAN protocol

• Only supports cars and

trucks between 1996-2003

• Only allows user to read

and clear DTCs

see http://www.amazon.com/OBDII-Engine-Scanner-Trouble-Reader/dp/B000LEPT5G/ref=sr_1_1?ie=UTF8&qid=1352273604&sr=8-1&keywords=U380 for information on this hand-held scanner

Expensive Hand-held ScannerInnova 3130c DTC Scanner

• $208.16 + shipping on Amazon

• Compatible with cars manufactured beyond 1996

• Wifi connectivity, allows connection to Fix Assist database

• Fix Assist has a database of fixes

for common DTCs

• LED lights indicate whether car will

pass or fail emission testssee http://www.amazon.com/Innova-3130c-Diagnostic-Scanner-Vehicles/dp/B008RHBJ8K/ref=sr_1_2?ie=UTF8&qid=1352273755&sr=8-2&keywords=innova+3130c for information on this hand-held scanner

OBD Products

• Hand-held scan tools

• Mobile device based tools and analysis

• PC based scan tools and analysis

Mobile Device Based Tools

• Many iPhone and Android applications

• Use an OBD II to bluetooth connection

• Advantages: much cheaper for the same amount of capabilities, more flexible, better user interface

• Disadvantages: phone many not be compatible with smartphone software

ELM 327 OBD-II to Bluetooth Connector

• $23.99 + shipping and handling on Amazon.com

• Works with Torque Pro Android application among 100s of others

Torque Pro (Android Application)

• $4.95

• Over 10,000 reviews, with an average rating of 5 stars out of 5

• Supports Torque measurements, speed measurements, fuel efficiency, among 100s of other types of engine logging

• Maps logged data against GPS

Torque Pro (Android Application)

Applications

• Hand-held scan tools

• Mobile device based tools and analysis

• PC based scan tools and analysis

PC Based Scan Tools and Analysis

• Similar to the mobile solutiono except more access to different types of peripheral

interfaces (serial, usb, etc.)o less portable

• Typically used by professional mechanicso no need to be mobile in a mechanics shopo allows for faster diagnosis (more cpu power)o no worries about batteries dying

TouchScan OBD Software

• $24.95 (no shipping and handling) on scantool.net

• Offers many of the same features as Torque Pro o Customizable user interfaceo Error database lookupo ect.

TouchScan OBD Software

ODB-II - Hacker Friendly!

• ODB-II is simple and well known (tons of documentation)

• There is an Arduino OBD-II GPS logger!

• Hack away!

What did we learn?

• What OBD is and how we can use it to find out what is wrong with our engine

• The history of OBD and how the OBD protocol has progressed over time

• OBD II low level protocol in depth

• How we can retrieve DTC codes and engine data from OBD computer at a high level

• OBD consumer products

Any Questions?

Images:

1. http://www.autoobd2diagnostic.com/category/obd-diagnosc (image)

2. http://www.harborfreight.com/can-obd-ii-code-reader-eobd-scanner-98614.html

3.http://www.dinodirect.com/engine-memo-scanner-u380-obdii-obd2-eobd.html?cur=USD&affid=3846&gclid=CKK3z5mhqrMCFRBgMgod4WQAqw

4. http://www.arduinodev.com/ultimate-gps-obd-data-logger-displayer/

5. http://scantools.net

5. add all the others

Information:

1. http://epa.gov/obd/

2. http://en.wikipedia.org/wiki/On-board_diagnostics

3. http://en.wikipedia.org/wiki/ALDL

4. http://shieldedpair.net/BAE5030/Lectures/J1850%20Introduction.pdf

5. http://www.obd-codes.com/faq/obd2-codes-explained.php

Sources