CHAPTER 19 Onboard Diagnosis
OBJECTIVES After studying Chapter 19, the reader will be able to: • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic Systems Diagnosis). • Explain the purpose and function of onboard diagnosis. • List the various duties of the diagnostic executive (task master). • List five continuous monitors. • List five noncontinuous monitors.
California Air Resources Board (CARB) Component identification (CID) Comprehensive component monitor (CCM) Diagnostic executive Enable criteria Exponentially weighted moving average (EWMA) monitor Federal Test Procedure (FTP) Freeze-frame Functionality Malfunction indicator lamp (MIL) On-board diagnosis (OBD) Parameter identification (PID) Rationality Society of Automotive Engineers (SAE) Test identification (TID) Task manager KEY TERMS
ON-BOARD DIAGNOSTICS GENERATION-II (OBD-II) SYSTEMS • PURPOSE AND FUNCTION OF OBD II • The automotive industry calls these systems On-Board Diagnostics (OBDs). The California Air Resources Board (CARB) developed the first regulation requiring manufacturers selling vehicles in that state to install OBD. • OBD Generation I (OBD I) applies to all vehicles sold in California beginning with the 1988 model year.
FIGURE 19–1 A typical malfunction indicator lamp (MIL) often labeled “check engine.” ON-BOARD DIAGNOSTICS GENERATION-II (OBD-II) SYSTEMS
ON-BOARD DIAGNOSTICS GENERATION-II (OBD-II) SYSTEMS • OBD-II OBJECTIVES • Generally, the CARB defines an OBD-II-equipped vehicle by its ability to do the following: • 1. Detect component degradation or a faulty emissionrelated system that prevents compliance with federal emission standards. • 2. Alert the driver of needed emission-related repair or maintenance. • 3. Use standardized DTCs and accept a generic scan tool.
DIAGNOSTIC EXECUTIVE AND TASK MANAGER • On OBD-II systems, the PCM incorporates a special segment of software. • On Ford and GM systems, this software is called the diagnostic executive. • On Chrysler systems, it is called the task manager. • This software program is designed to manage the operation of all OBD-II monitors by controlling the sequence of steps necessary to execute the diagnostic tests and monitors.
MONITORS • A monitor is an organized method of testing a specific part of the system. • Monitors are simply tests that the computer performs to evaluate components and systems. • If a component or system failure is detected while a monitor is running, a DTC will be stored and the MIL illuminated by the second trip. • The two types of monitors are: • CONTINUOUS MONITORS • NONCONTINUOUS MONITORS
OBD-II MONITOR INFORMATIONCOMPREHENSIVE COMPONENT MONITOR • The circuits and components covered by the comprehensive component monitor (CCM) do not include those directly monitored by another monitor. • However, OBD II also requires that inputs from powertrain components to the PCM be tested for rationality, and that outputs to powertrain components from the PCM be tested for functionality. • Both inputs and outputs are to be checked electrically. • Rationality checks refer to a PCM comparison of input value to values.
OBD-II MONITOR INFORMATION • CONTINUOUS RUNNING MONITORS • ONCE PER TRIP MONITORS • EXPONENTIALLY WEIGHTED MOVING AVERAGE (EWMA) MONITORS • NONCONTINUOUS MONITORS
ENABLING CRITERIA • With so many different tests (monitors) to run, the PCM needs an internal director to keep track of when each monitor should run. • As mentioned, different manufacturers have different names for this director, such as the diagnostic executive or the task manager. • Each monitor has enabling criteria. • These criteria are a set of conditions that must be met before the task manager will give the go-ahead for each monitor to run.
ENABLING CRITERIA • Most enabling criteria follow simple logic, for example: • The task manager will not authorize the start of the O2S monitor until the engine has reached operating temperature and the system has entered closed loop. • The task manager will not authorize the start of the EGR monitor when the engine is at idle, because the EGR is always closed at this time.
ENABLING CRITERIA • TRIP • WARM-UP CYCLE • MIL CONDITION: OFF • MIL CONDITION: ON STEADY • MIL CONDITION: FLASHING • MIL: OFF
OBD-II DTC NUMBERING DESIGNATION • A scan tool is required to retrieve DTCs from an OBD-II vehicle. • Every OBD-II scan tool will be able to read all generic Society of Automotive Engineers (SAE) DTCs from any vehicle.
FIGURE 19–2 OBD-II DTC identification format. OBD-II DTC NUMBERING DESIGNATION
OBD-II DTC NUMBERING DESIGNATION • DTC NUMBERING EXPLANATION • TYPES OF DTCS • TYPE A CODES • TYPE B CODES • TYPE C AND D CODES • DIAGNOSTIC TROUBLE CODE PRIORITY
OBD-II FREEZE-FRAME • To assist the service technician, OBD II requires the computer to take a “snapshot” or freeze-frame of all data at the instant an emission-related DTC is set. • A scan tool is required to retrieve this data.
OBD-II FREEZE-FRAME • Freeze-frame items include: • Calculated load value • Engine speed (RPM) • Short-term and long-term fuel trim percent • Fuel system pressure (on some vehicles) • Vehicle speed (mph) • Engine coolant temperature • Intake manifold pressure • Closed-open-loop status • Fault code that triggered the freeze-frame
What Are Pending Codes? • Pending codes are set when operating conditions are met and the component or circuit is not within the normal range, yet the conditions have not yet been met to set a DTC. For example, a sensor may require two consecutive faults before a DTC is set. If a scan tool displays a pending code or a failure, a driveability concern could also be present. The pending code can help the technician to determine the root cause before the customer complains of a check engine light indication.
ENABLING CONDITIONS OR CRITERIA • These are the exact engine operating conditions required for a diagnostic monitor to run. • Example: • Specific RPM • Specific ECT, MAP, run time, VSS, etc. • PENDING • CONFLICT • SUSPEND
PCM TESTS • RATIONALITY TEST • FUNCTIONALITY TEST • ELECTRICAL TEST
GLOBAL OBD-II • All OBD-II vehicles must be able to display data on a global (also called generic) scan tool under nine different modes of operation. • The global (generic) data is used by most state emission programs. • Global OBD-II displays often use hexadecimal numbers, which use 16 numbers instead of 10. • The numbers 0 to 9 (zero counts as a number) make up the first 10 and then capital letters A to F complete the 16 numbers. • To help identify the number as being in a hexadecimal format, a dollar sign ($) is used in front of the number or letter
How Can You Tell Generic from Factory? • When using a scan tool on an OBD-II-equipped vehicle, if the display asks for make, model, and year, then the factory or enhanced part of the PCM is being accessed. If the generic or global part of the PCM is being scanned, then there is no need to know the vehicle details.
SUMMARY • If the MIL is on, retrieve the DTC and follow the manufacturer’s recommended procedure to find the root cause of the problem. • All monitors must have the enable criteria achieved before a test is performed. • OBD-II vehicles use common generic DTCs. • OBD II includes generic (SAE), as well as vehicle manufacturerspecific DTCs, and data display.
REVIEW QUESTIONS • What does the PCM do during a trip to test emissionrelated components? • What is the difference between a type A and type B OBD-II DTC? • What is the difference between a trip and a warm-up cycle? • What could cause the MIL to flash?
CHAPTER QUIZ 1. A freeze-frame is generated on an OBD-II vehicle ________. • When a type C or D diagnostic trouble code is set • When a type A or B diagnostic trouble code is set • Every other trip • When the PCM detects a problem with the O2S
CHAPTER QUIZ 2. An ignition misfire or fuel mixture problem is an example of what type of DTC? • Type A • Type B • Type C • Type D
CHAPTER QUIZ 3. The comprehensive component monitor checks computercontrolled devices for_______. • Opens • rationality • shorts-to-ground • All of the above
CHAPTER QUIZ 4. OBD II has been on all passenger vehicles in the United States since ________. • 1986 • 1991 • 1996 • 2000
CHAPTER QUIZ 5. Which is a continuous monitor? • Fuel system monitor • EGR monitor • Oxygen sensor monitor • Catalyst monitor
CHAPTER QUIZ 6. DTC P0302 is a ________. • Generic DTC • Vehicle manufacturer-specific DTC • Idle speed-related DTC • Transmission/transaxle-related DTC
CHAPTER QUIZ 7. Global (generic) OBD II contains some data in what format? • Plain English • Hexadecimal • Roman numerals • All of the above
CHAPTER QUIZ 8. By looking at the way diagnostic trouble codes are formatted, which DTC could indicate that the gas cap is loose or defective? • P0221 • P1301 • P0442 • P1603
CHAPTER QUIZ 9. The computer will automatically clear a DTC if there are no additional detected faults after ________. • Forty consecutive warm-up cycles • Eighty warm-up cycles • Two consecutive trips • Four key-on/key-off cycles
CHAPTER QUIZ 10. A pending code is set when a fault is detected on ________. • A one-trip fault item • The first fault of a two-trip failure • The catalytic converter efficiency • Thermostat problem (too long to closed-loop status)