1. On Board Diagnostics OBD
Rebecca Doebler, James Carl, Joe Romeo
EECS 498

2. 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

3. 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

4. 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
other stuff, rpm, hp

5. 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

6. 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

7. 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 for more information about OBD history

8. 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

9. Why is my check engine light on?
We use DTCs or Diagnostic Trouble Codes to determine the problem
Example:
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

10. Diagnostic Trouble Codes (DTCs)
Older OBD protocols have fewer DTCs and are not standardized
Newer OBD protocols have many more DTCs
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
hard to read

11. DTCs (cont) Second Digit - Code Type Third Digit - Sub-System
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)
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
Fourth and Fifth Digits
These digits, along with the others, are variable, and relate to a particular problem. For example,a P0171 code means P System Too Lean (Bank 1).
bad formatting

12. 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

13. Standard Interfaces - ALDL
ALDL - Assembly line diagnostic link
Developed by GM prior to OBD I
System was only vaguely standardized
Specifics for communication link varied based on model
Diagnostic Connector:
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 ALDL- ground, battery-voltage and a single line for data
Most other pins used for additional diagnostic information and control interfaces

14. Standard Interfaces - ALDL (cont)
Example 12-pin connector:
Data Stream:
Unidirectional data (earlier versions)
Serially transmitted at a baud rate of 160 using PWM
Bidirectional data (later versions) at a baud rate of
Request-driven

15. 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

16. Standard Interfaces - OBD 1.5
Partial implementation of OBD II
Same pinout as OBD II
Fewer fault codes

17. 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

18. 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

19. Connector http://www.carplugs.com/Product_view_Cables_2.html

20. OBD-II Signal Protocols
Five Signal Protocols
SAE J Pins 2 and 10
PWM - Ford
VPW - GM
ISO 9141/ Pins 7 and 15
Serial communication
Used by Chrysler and Europeans
ISO Pin 6 and 14
CAN communication
Used by all since 2008

21. SAE J1850 PWM/VPW PWM VPW 41.6 Kb/s using pin 2 as Bus +, 10 Bus -
Developed by Ford
Differential Voltage Signaling
High is +5V differential
10 byte message
VPW
10.4 Kb/s using just pin 2 as Bus +
Developed by GM
Single wire voltage signaling
~7V High, <3.5V Low

22. PWM Signaling

23. VPW Signaling get rid of the circuit

24. Message Frame - PWM/VPW
SOF - High signal for 200us
Header - 1 or 3 bytes
Priority 3 bits, 000 low priority, 111 high priority
Header type, 0 means three byte header, 1 means single byte
In frame response, 0 means IFR required
Address mode, functional address(0), physical(1)
Message type, two bits
Data
CRC - Cyclic redundancy check, a type of error checking
NB - Normalized Bit

25. CRC - Cyclic Redundancy Check
Error Checking
1 byte checksum
Sequentially calculated
Implemented with XOR gates
Generator Polynomial - 0x1D

26. 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

27. ISO CAN
1 Mbit/s
Must be implemented on all cars built after 2008

28. ISO CAN Message Frame

29. 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

30. High Level Overview of OBD II
Send request over CAN bus
Request is a 1 to 2 byte message
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
size varies depending on request
see for information on different modes and PIDs

31. 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 for information on different modes and PIDs

32. Example 1 Send request over CAN bus
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

33. Example 2 Send request over CAN bus
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
temperature readings can be between -40 and 215
so to get our temperature reading, we do (received message - 40)
citation

34. 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

35. OBD Products Hand-held scan tools
Mobile device based tools and analysis
PC based scan tools and analysis

36. OBD Products Hand-held scan tools
Mobile device based tools and analysis
PC based scan tools and analysis

37. 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
more expensive models have things like bluetooth connection, live data feeds

38. Cheap Hand-held Scanner U380 Engine Check OBD-II Scanner
Very cheap ($ shipping on Amazon)
Doesn't support the CAN protocol
Only supports cars and
trucks between
Only allows user to read
and clear DTCs
see for information on this hand-held scanner

39. Expensive Hand-held Scanner Innova 3130c DTC Scanner
$ 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 tests
more expensive models have things like bluetooth connection, live data feeds
see for information on this hand-held scanner

40. Mobile device based tools and analysis
OBD Products
Hand-held scan tools
Mobile device based tools and analysis
PC based scan tools and analysis

41. 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
more flexible because it is easier to push new software on android that supports new cars, versus trying to buy new hardware every time a new car comes out with new OBD-II capabilities

42. ELM 327 OBD-II to Bluetooth Connector
$ shipping and handling on Amazon.com
Works with Torque Pro Android application among 100s of others

43. 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

44. Torque Pro (Android Application)

45. PC based scan tools and analysis
Applications
Hand-held scan tools
Mobile device based tools and analysis
PC based scan tools and analysis

46. PC Based Scan Tools and Analysis
Similar to the mobile solution
except more access to different types of peripheral interfaces (serial, usb, etc.)
less portable
Typically used by professional mechanics
no need to be mobile in a mechanics shop
allows for faster diagnosis (more cpu power)
no worries about batteries dying

47. TouchScan OBD Software
$24.95 (no shipping and handling) on scantool.net
Offers many of the same features as Torque Pro
Customizable user interface
Error database lookup
ect.

48. TouchScan OBD Software

49. ODB-II - Hacker Friendly!
ODB-II is simple and well known (tons of documentation)
There is an Arduino OBD-II GPS logger!
Hack away!

50. 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

51. Any Questions?

52. Sources
Images:
1. (image) 2.
3. eobd.html?cur=USD&affid=3846&gclid=CKK3z5mhqrMCFRBgMgod4WQAqw 4. 5.
5. add all the others
Information: 1. 2. 3. 4. 5.