On Board Diagnostics
OBD
Rebecca Doebler, James Carl, Joe Romeo
EECS 498
What we will learn today
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What is OBD?
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History of OBD
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DTC (Diagnostic Trouble Codes)
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Progression of the OBD protocol over time
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Low level implementation of OBD II protocol
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High level overview of OBD II protocol
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OBD Products
OBD (On Board Diagnostics)
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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?
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On-board diagnostics
Source: 1
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 onboard computers and diagnose any potential
failures in the engine, as well as retrieve
information such as rpm, horse-power, etc.
Why is OBD important?
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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)
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What is OBD?
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History of OBD
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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
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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)
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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?
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We use DTCs or Diagnostic Trouble Codes
to determine the problem
Example:
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An electronic control module uses an oxygen sensor
to monitor exhaust gas for being rich or lean
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)
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Older OBD protocols have fewer DTCs and
are not standardized
Newer OBD protocols have many more
DTCs
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Latest OBD protocol has a five digit DTC
First Character - System
The first character identifies identifies the system related to the trouble
code.
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P = Powertrain
B = Body
C = Chassis
U = Undefined
DTCs (cont)
Second Digit - Code Type
The 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)
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Third Digit - Sub-System
The 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
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Fourth and Fifth Digits
These 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)
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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
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ALDL - Assembly line diagnostic link
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Developed by GM prior to OBD I
System was only vaguely standardized
Specifics for communication link varied based on
model
Diagnostic Connector:
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At least four different connectors used with ALDL
12-pin connector was most widely used for GM
Generally only three pins were used for basic ALDLground, battery-voltage and a single line for data
Most other pins used for additional diagnostic
information and control interfaces
Standard Interfaces - ALDL (cont)
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Example 12-pin connector:
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Data Stream:
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Unidirectional data (earlier versions)
Serially transmitted at a baud rate of 160 using
PWM
Bidirectional data (later versions) at a baud rate of
8192
Standard Interfaces - OBD I
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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
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Partial implementation of OBD II
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Same pinout as OBD II
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Fewer fault codes
Quick Recap
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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)
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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
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Five Signal Protocols
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SAE J1850 - Pins 2 and 10
 PWM - Ford
 VPW - GM
ISO 9141/14230 - Pins 7 and 15
 Serial communication
 Used by Chrysler and Europeans
ISO 15765 - Pin 6 and 14
 CAN communication
 Used by all since 2008
SAE J1850 PWM/VPW
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PWM
41.6 Kb/s using pin 2 as Bus +, 10 Bus o Developed by Ford
o Differential Voltage Signaling
o High is +5V differential
o 10 byte message
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VPW
10.4 Kb/s using just pin 2 as Bus +
o Developed by GM
o Single wire voltage signaling
o ~7V High, <3.5V Low
o 10 byte message
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PWM Signaling
http://shieldedpair.net/BAE5030/Lectures/J1850%20Introduction.pdf
VPW Signaling
http://shieldedpair.net/BAE5030/Lectures/J1850%20Introduction.pdf
Message Frame - PWM/VPW
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SOF - High signal for 200us
http://shieldedpair.net/BAE5030/Lectures/J1850%20Introduction.p
df
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
CRC - Cyclic Redundancy Check
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Error Checking
1 byte checksum
Sequentially calculated
Implemented with XOR gates
Generator Polynomial - 0x1D
ISO 9141/ISO 14230 KWP2000
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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
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1 Mbit/s
Must be implemented on
all cars built after 2008
ISO 15765 CAN Message Frame
OBD (On Board Diagnostics)
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What is OBD?
History of OBD
DTC (Diagnostic Trouble Codes)
Progression of the OBD protocol over time
Low level implementation of OBD II protocol
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High level overview of OBD II protocol
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OBD Products
High Level Overview of OBD II
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Send request over CAN bus
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Request is a 1 to 2 byte message
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message is between 1 and 2 bytes long, consisting
of a mode, and followed by a PID when necessary
OBD II responds with a message
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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
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Send request over CAN bus
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in this case, we'll send mode 0x03 (show stored
DTC's)
doesn't require a PID
OBD II responds with all of the stored DTC's
Example 2
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Send request over CAN bus
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in this case, we'll send mode 0x01 followed by PID
0x05
remember, 0x01 is the mode for current data, and
PID 0x05 specifies engine coolant temperature
OBD II responds with a 1 byte message
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temperature readings can be between -40 and 215
so to get our temperature reading, we do (received
message - 40)
OBD (On Board Diagnostics)
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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
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Hand-held scan tools
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Mobile device based tools and analysis
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PC based scan tools and analysis
OBD Products
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Hand-held scan tools
Mobile device based tools and analysis
PC based scan tools and analysis
Hand-held Scan Tools
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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
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Very cheap ($20.88 + shipping on Amazon)
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Doesn't support the CAN protocol
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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 Scanner
Innova 3130c DTC Scanner
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$208.16 + shipping on Amazon
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Compatible with cars manufactured beyond 1996
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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 tests
see 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
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Hand-held scan tools
Mobile device based tools and
analysis
PC based scan tools and analysis
Mobile Device Based Tools
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Many iPhone and Android applications
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Use an OBD II to bluetooth connection
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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
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$23.99 + shipping and handling on
Amazon.com
Works with Torque Pro Android application
among 100s of others
Torque Pro (Android Application)
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$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
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Hand-held scan tools
Mobile device based tools and analysis
PC based scan tools and analysis
PC Based Scan Tools and Analysis
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Similar to the mobile solution
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except more access to different types of peripheral
interfaces (serial, usb, etc.)
less portable
Typically used by professional mechanics
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no need to be mobile in a mechanics shop
allows for faster diagnosis (more cpu power)
no worries about batteries dying
TouchScan OBD Software
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$24.95 (no shipping and handling) on
scantool.net
Offers many of the same features as Torque
Pro
Customizable user interface
o Error database lookup
o ect.
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TouchScan OBD Software
ODB-II - Hacker Friendly!
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ODB-II is simple and well known (tons of
documentation)
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There is an Arduino OBD-II GPS logger!
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Hack away!
What did we learn?
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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?
Sources
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-obd2eobd.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