1. CHAPTER 49
On-Board Diagnostics

2. Introduction (1 of 2)
Emissions from automobiles can harm the environment, as well as our health.
They need to be monitored and kept in check.
The United States Congress passed federal emission regulations, starting with the Clean Air Act in 1963.

3. Introduction (2 of 2)
Vehicle emission testing and repair remedies are a big part of day-to-day business.
When a vehicle’s malfunction indicator lamp (MIL)—formerly called a “check engine light”—is illuminated, it means the vehicle is not complying with clean air regulations.

4. Pollutants (1 of 7)
Vehicles emit evaporative emissions, known as volatile organic compounds (VOCs), to the atmosphere.
VOCs may be fuel or oil vapors emitted from the fuel tank, fuel lines, engine crankcase, or tailpipe.

5. Pollutants (2 of 7) Pollutants include: Carbon monoxide (CO)
Hydrocarbons (HCs) or VOCs
Particulate matter (PM)
Carbon dioxide (CO2)
Sulfur dioxide (SO2)
Oxides of nitrogen—nitric oxide (NO) and nitrogen dioxide (NO2)

6. Pollutants (3 of 7)
Oxides of nitrogen and hydrocarbons react together to create ground-level ozone, which is considered a health hazard.
Ground-level ozone especially affects children, the elderly, and those with respiratory problems.

7. Pollutants (4 of 7)
Pollutants are monitored and controlled by efficient on-board systems using state-of-the-art electronics.
Closed-loop electronic systems have assumed the major responsibility of cleaning up vehicle emissions.

8. Pollutants (5 of 7)
Strategies devised for curtailing light-duty vehicle emissions in the United States since the 1960s:
1961—First positive crankcase ventilation (PCV) systems required in California
1964—Sealed crankcase systems replace crankcase “draft tubes”
1968—Controls for crankcase VOCs, tailpipe CO, and hydrocarbons (PCV, AIR, etc.)

9. Pollutants (6 of 7) Strategies to curtail emissions (cont’d):
1969—Commencement of limiting oxides of nitrogen emissions by retarding ignition and valve timing
1971—Introduction of evaporative emission (EVAP) control systems (charcoal canisters)
1973—Exhaust gas recirculation (EGR) systems used to control oxides of nitrogen
1975—Unleaded gasoline phased in
1975—Oxidizing catalytic converters introduced

10. Pollutants (7 of 7) Strategies to curtail emissions (cont’d):
1981—Closed-loop systems and three-way catalysts introduced; first-generation on-board diagnostics (OBDI) enacted nationwide
1996—Second-generation on-board diagnostics (OBDII) enacted nationwide
1998—Commencement of vehicle refueling emission controls
2003—Widespread adoption of controller area network (CAN) communication systems

11. On-Board Diagnostic Systems (1 of 6)
On-board diagnostic systems use powerful on-board computers to pinpoint problems in vehicle systems and components.
On-board computers inform the vehicle operator when a fault occurs.
Assist technicians in identifying and repairing malfunctioning circuits or components

12. On-Board Diagnostic Systems (2 of 6)
In the United States, two different types of OBD systems have been used.
OBDI: The first generation of on-board diagnostic systems (1981)
Monitored mainly for parts and wiring malfunctions

13. On-Board Diagnostic Systems (3 of 6)
Types of OBD systems (cont’d)
OBDII: The second generation of on-board diagnostic systems
Operates under standards set by the Society of Automotive Engineers (SAE) to conform to US Environmental Protection Agency (EPA) regulations
Tests vehicle operating systems for faults affecting drivability, vehicle safety, and emission efficiency

14. On-Board Diagnostic Systems (4 of 6)
Both OBDI and OBDII systems provide standards regarding nomenclature (names of parts) and fault description codes.
OBDII faults and background data can be accessed and read by aftermarket as well as original equipment manufacturer (OEM) test equipment.

15. On-Board Diagnostic Systems (5 of 6)
The data link connector (DLC) enables the scanner to access data stored in the vehicle’s various computers.

16. On-Board Diagnostic Systems (6 of 6)
The DLC is a 16-pin connector with a common (SAE J1962) size and shape.
Regardless of vehicle make and model, its location is now fairly standardized as being within 2' of the steering wheel below the driver’s side instrument panel.

17. OBD Terminology
Before the SAE published the appropriate “recommended practices,” OEMs used nonstandardized nomenclature.
The SAE has helped standardize automotive terms used by engineers and technicians.
A complete listing of OBDI and OBDII terms is available from the SAE (SAE J1930).

18. CAN-Bus (1 of 3)
To simplify wiring, controller area networks (CANs) have become commonplace in today’s vehicles.
A CAN is a localized (on-board) vehicle network that enables computers and components to send and receive signals across a shielded twisted pair of wires.

19. CAN-Bus (2 of 3)
The shielded pair of wires forms a loop around the vehicle to connect components and handle encoded messages between them.
The various computers/modules can network, or “talk,” to one another.
The CAN-bus is constantly monitored by the OBDII system.

20. CAN-Bus (3 of 3)
Data can be accessed by using the appropriate scan tool to either read data or command actuator functions to operate.

21. Diagnostic Trouble Codes (1 of 7)
Diagnostic trouble codes (DTCs) indicate the component or circuit in which a fault has been detected.
Codes are “set” (stored) in one or more of the vehicle’s on-board computers once a fault is detected.

22. Diagnostic Trouble Codes (2 of 7)
A fault is generated when values being monitored determine the emissions would be 1.5 times the EPA Federal Test Procedure (FTP).
Emission-related DTCs are the same across all vehicle makes and models, as are the SAE-recommended names used to describe components and systems.

23. Diagnostic Trouble Codes (3 of 7)
The malfunction indicator lamp (MIL)

24. Diagnostic Trouble Codes (4 of 7)
If a vehicle system reports that a fault exists, the MIL located in the instrument cluster will likely illuminate.
Even a loose gas cap can trigger a DTC and illuminate the MIL under certain conditions.
Once a malfunction occurs, the MIL will remain on until the system returns to normal or the fault is seen as repaired.

25. Diagnostic Trouble Codes (5 of 7)
Both OBDI and OBDII systems monitor engine sensors, fuel delivery components, and emission control devices that, if faulty, will cause problems.
OBDI systems are normally limited to the detection of an open or short in a sensor or wiring.

26. Diagnostic Trouble Codes (6 of 7)
OBDII systems monitor all emission-related components and circuits for opens, shorts, abnormal operation, and more.
OBDII codes use a series of letters and numbers grouped together to identify which system, component, or circuit is at fault.

27. Diagnostic Trouble Codes (7 of 7)
Interpreting DTCs
First character identifies whether fault is located within power train (P), body (B), chassis controller (C), or communication system (U).
Next four are numbers, starting with 0 or 1.
0 = generic OBDII code; 1 = OEM code
Next three numbers identify system and component related to fault.

28. Freeze-Frame Data (1 of 3)
Since OBDII came about in 1996, technicians can access freeze-frame snapshots that are automatically recorded in the PCM when a fault occurs.
If a more serious fault supersedes another previously less-serious recorded fault, freeze-frame data are updated.

29. Freeze-Frame Data (2 of 3)
Difficult-to-find intermittent faults can be diagnosed by carefully reviewing data stored just before, during, and after the fault occurred.
Modern scan tools can retrieve freeze-frame data and display them (via a graphing scan tool) for analysis after the fact.

30. Freeze-Frame Data (3 of 3)
A scan tool can retrieve and display freeze-frame data.

31. System Monitors (1 of 2)
A vehicle’s computer (PCM) must monitor emission systems with two priorities in mind.
Continuous monitoring of systems and components that could contribute to major emission failures
Possible faults include engine misfiring and an incorrect air/fuel mixture.

32. System Monitors (2 of 2) Priorities of PCM (cont’d)
Noncontinuous monitoring of lower-priority faults
Systems are checked only once during each engine warm-up cycle or less, depending on certain circumstances such as ambient temperatures or fuel level.

33. Drive Cycles (1 of 3)
A drive cycle is essentially considered to include the following events:
A vehicle starts, warms up, is accelerated, cruises, slows down, accelerates once more, decelerates, stops, and cools down.

34. Drive Cycles (2 of 3)
The EPA has established “drive cycles” for emission testing of various kinds of vehicles.
Light-duty vehicle (240-second) drive cycle is the basis for how OBDII monitors (tests) are run.
A complete driving cycle should include diagnostics on all systems and be completed in under 15 minutes.

35. Drive Cycles (3 of 3) EPA drive cycles (cont’d)
Certain monitors cannot be run during a drive cycle if qualifying conditions are not met.
An evaporative emission (EVAP) monitor will not run if the fuel tank is nearly full or nearly empty.
Particular monitors cannot run until after others have been run and passed.
EVAP monitoring will not run if the engine coolant temperature monitor has not passed.

36. Scan Tools (1 of 4)
A scan tool (“scanner”) can electronically communicate with and extract data from the vehicle’s one or more on-board computers.
On-board computer modules
PCM, electronic brake control module (EBCM), body control module (BCM), transmission control module (TCM), etc.

37. Scan Tools (2 of 4)
Scanners monitor engine compression, vacuum, and internal engine anomalies.
Bidirectional scanners cause various components and systems to operate for test purposes.

38. Scan Tools (3 of 4)
Scanners are used along with digital storage oscilloscopes, portable five-gas emission analyzers, and other diagnostic equipment for much more effective time-saving diagnostic routines.

39. Scan Tools (4 of 4)
A fault code does not necessarily point directly to the problem.
Example: A P0171 Fuel System Too Lean code may mean a defective oxygen sensor, but could mean an underreporting mass airflow sensor, a vacuum leak, use of the wrong fuel, etc.
Further testing is often required.

40. Diagnosis and Testing (1 of 24)
Modern vehicle engine systems provide performance and efficient use of fuel while ensuring that exhaust emissions meet strict environmental regulations.
Engineers have improved the performance of mechanical components to ensure the highest possible efficiency while reducing exhaust emissions.

41. Diagnosis and Testing (2 of 24)
To diagnose faults correctly:
Test for the cause of the customer’s concern. Determine what faults may cause the symptoms.
Check mechanical, electrical, ignition, and fuel system to identify location and types of faults.
A vehicle may have multiple faults.

42. Diagnosis and Testing (3 of 24)
Test equipment needed to diagnose engine faults:
ODB scanners
Digital storage oscilloscopes
Compression gauges
Digital volt-ohmmeters (DVOMs)
Fuel system pressure gauges
Flowmeters

43. Diagnosis and Testing (4 of 24)
Retrieving and recording DTCs, monitor status, and freeze-frame data are integral steps in diagnosing faults.
Must be able to do so anytime a vehicle sets a DTC or fails emission monitors

44. Diagnosis and Testing (5 of 24)
Every vehicle sold is required to meet a drive cycle, which is designed to simulate actual driving conditions.
The OBDII system constantly tests and analyzes each system’s performance over the drive cycle.
The PCM will set and store DTCs if a fault is detected.

45. Diagnosis and Testing (6 of 24)
Diagnosing the cause of drivability or emission concerns with DTCs
DTCs often indicate a fault within vehicle systems such as with drivability or emission concerns.
DTCs are a good place to commence the diagnostic process.
Retrieve all codes and record them electronically or print them out.

46. Diagnosis and Testing (7 of 24)
Diagnosing concerns with DTCs (cont’d)
Diagnosis requires analysis of the code’s meaning and the system it relates to.
Manufacturer’s information or aftermarket code lists are required.
Codes indicate that a system is not functioning correctly.
Multiple codes may be set.
Some codes may indicate cause of problem; some may result from system malfunction.

47. Diagnosis and Testing (8 of 24)
Diagnosing drivability or emission concerns without DTCs
A vehicle may fail an emission test or a customer may complain about a drivability issue even though DTCs have not been set.
Absence of DTC does not mean the vehicle is running perfectly.

48. Diagnosis and Testing (9 of 24)
Diagnosing concerns without DTCs (cont’d)
The ODBII system sets fault codes if vehicle exceeds programmed limits for EPA’s FTP.
Pass and fail points differ for every vehicle.
Are integrated within the system’s operation to keep emissions in check even in the event of a fault

49. Diagnosis and Testing (10 of 24)
Diagnosing concerns without DTCs (cont’d)
PCM can make adjustments to ensure engine emissions continue to meet the standard.
Adjustments may affect drivability, but because requirements are still met, no DTC is set.

50. Diagnosis and Testing (11 of 24)
Diagnosing concerns without DTCs (cont’d)
To diagnose a vehicle when DTCs have not been set:
Use scan tools to read system parameters, digital oscilloscopes, DVOMs, smoke machines, pressure gauges, and flowmeters.
Collect info and narrow down the fault’s cause.

51. Diagnosis and Testing (12 of 24)
Diagnosing concerns without DTCs (cont’d)
To diagnose drivability or emission concerns that do not involve DTCs:
Gather information on the complaint from the customer.
Verify the complaint and identify the symptoms.
Interpret the results and diagnose the drivability or emission concerns, and recommend a course of action.

52. Diagnosis and Testing (13 of 24)
Testing computerized engine control system sensors, the PCM, actuators, and circuits
Graphing multimeters and digital storage oscilloscopes
Enable precise electrical measurements over time Display the results on a graph as a waveform
Are essential in checking electrical and electronic signals to and from sensors and PCMs

53. Diagnosis and Testing (14 of 24)
Testing sensors, the PCM, actuators, circuits (cont’d)
Graphing multimeters and digital storage oscilloscopes (cont’d)
Given today’s complex systems, these tools are essential in checking electrical and electronic signals to and from sensors and PCMs.
Verify signals to and from electrical and electronic components

54. Diagnosis and Testing (15 of 24)
An oscilloscope being used to check electrical and electronic signals to and from a sensor

55. Diagnosis and Testing (16 of 24)
Diagnosing drivability and emission problems resulting from malfunctions of interrelated systems
Can be caused by interrelated systems, such as automatic transmissions, cruise control, security systems, suspension control, air conditioning, and other non-OEM–installed accessories

56. Diagnosis and Testing (17 of 24)
Diagnosing problems of interrelated systems (cont’d)
Each system, aside from the non-OEM accessories is controlled by a system computer and has electronic diagnostic capability and associated fault codes.
Understand how each system works and interacts with other systems.

57. Diagnosis and Testing (18 of 24)
Diagnosing problems of interrelated systems (cont’d)
Non-OEM–installed accessories can make diagnosing difficult due to a lack of information and knowledge about the products, their installation, and how they work.
Ensure that as much information as possible is gathered from the customer before commencing work.

58. Diagnosis and Testing (19 of 24)
Testing actuators
Actuators are devices such as solenoids, fuel injectors, and stepper motors.
Used to convert electrical signals into mechanical movement
Test, check for correct signals to the actuator as well as the mechanical and electrical operation of the actuator.

59. Diagnosis and Testing (20 of 24)
Testing actuators (cont’d)
Testing may involve test equipment such as DVOMs, digital storage oscilloscopes, and pressure gauges, and other tools such as jumper leads and power supplies.
Always:
Check manufacturer’s info for voltages.
Isolate an actuator from its control circuit before applying any external voltage or power supply to test its operation.

60. Diagnosis and Testing (21 of 24)
Testing actuators (cont’d)
Never jump battery or power supply voltages to an actuator while it is connected to its control circuit.
Doing so may result in damage to the system computer.

61. Diagnosis and Testing (22 of 24)
Interpreting DTCs and scan tool data related to the emission control systems
Interpret DTCs and scan tool data when there is a drivability or emission problem.
Scan tools are an important test instrument for modern vehicles.
Allow access to the OBD and data systems

62. Diagnosis and Testing (23 of 24)
Interpreting data related to the emission control systems (cont’d)
Scan tools fall into two main categories—aftermarket and OEM.
OEM scanners are specific to a vehicle and often provide functionality that aftermarket scanners cannot.
Aftermarket scanners usually work on multiple manufacturers’ products, but not always as functional as an OEM scan tool.

63. Diagnosis and Testing (24 of 24)
Interpreting data related to the emission control systems (cont’d)
The scan tool is connected via the diagnostic plug.
Allows access to stored fault codes and vehicle data
Never erase data or fault codes before they have been accurately recorded.

64. Summary (1 of 6)
Second-generation on-board diagnostics (OBDII) started in late 1995 and became standard in All vehicles use the same generic adapter for a generic scan tool to connect to the vehicle’s computer.
Since California’s emission laws of the 1960s, the standards for emissions have gotten more stringent, requiring many changes to subsequent vehicles.

65. Summary (2 of 6)
OBD systems help the technician work more efficiently and help take the guesswork out of diagnosing problems on today’s sophisticated vehicles.
OBD systems are a great resource, using powerful on-board computers in harmony with sophisticated diagnostic equipment to pinpoint problems in vehicle systems and components.

66. Summary (3 of 6)
Both OEM and aftermarket OBDII scan tools serve to access OBD information via the data link connector (DLC).
The Society of Automotive Engineers (SAE) has standardized the terminology of parts and systems nomenclature (J1930) and across-the-board identification of generic DTCs (J2012).

67. Summary (4 of 6)
Diagnostic trouble codes (DTCs) are usually set after the vehicle has had two drive cycles with the same malfunction.
Codes on OBD systems are categorized as power train (P), body (B), chassis controller (C), and communications system (U).

68. Summary (5 of 6)
Freeze-frame data are the best way for a technician to determine the conditions under which a concern happens, which then helps determine the cause of the DTC.
Scan tools, a lab scope, and a digital volt-ohmmeter (DVOM) are a technician’s best tools when it comes to troubleshooting an OBD code.

69. Summary (6 of 6)
Always refer to the manufacturer’s service information and follow the diagnostic flowcharts to ensure that the vehicle malfunction is identified and repaired correctly.
Always use wiring diagrams when diagnosing any electric/electronic circuits in the OBD system, and do not forget about the grounds.

70. Credits
Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning.