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TitleOn Board Diagnostic II (Obd II)
File Size3.6 MB
Total Pages191
Table of Contents
                            obd2help
DriveabilityDiagnostics
OBDII_and_Emissions_Testing
	The OBDII Home Page
OBDII_Past_Present_Future
	AutoTap – OBDII Automotive Diagnostic Tool
intro_to_obd2
OBD_ganesan_w2
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Introduction to On Board Diagnostics (II)
	Powertrain and Emission Controls in Passenger Vehicles
	Powertrain and Emission Controls in Passenger Vehicles (contd)
	Powertrain and Emission Controls in Passenger Vehicles (contd)
	Powertrain and Emission Controls in Passenger Vehicles (contd)
	Powertrain and Emission Controls in Passenger Vehicles (contd)
	Powertrain and Emission Controls in Passenger Vehicles (contd)
	Powertrain and Emission Controls in Passenger Vehicles (contd)
	Powertrain and Emission Controls in Passenger Vehicles (contd)
	Powertrain and Emission Control in Passenger Vehicles (contd)
	Powertrain and Emission Controls in Passenger Vehicles (contd)
	Powertrain and Emission Controls in Passenger Vehicles (contd)
	
	Powertrain and Emission Controls in Passenger Vehicles (contd)
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	OBD II for L & MD Vehicles STD Manual
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	
	
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	
	
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Fundamentals of Powertrain Control strategies & OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II 6141Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Idle air control (IAC) valve
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Sensors and Actuators Employed in OBD II Diagnostics
	Functionality of Powertrain Control Module (PCM) in OBD II Diagnostics
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II
	Functionality of Powertrain Control Module (PCM) in OBD II Diagnostics
	Functionality of Powertrain Control Module (PCM) in OBD II Diagnostics
	Functionality of Powertrain Control Module (PCM) in OBD II Diagnostics
	Functionality of Powertrain Control Module (PCM) in OBD II Diagnostics
	Functionality of Powertrain Control Module (PCM) in OBD II Diagnostics
	Functionality of Powertrain Control Module (PCM) in OBD II Diagnostics
	Functionality of Powertrain Control Module (PCM) in OBD II Diagnostics
                        
Document Text Contents
Page 1

Automotive Repair Library, Auto Parts, Accessories, Tools & Equipment, Manuals & Books, Car BLOG, Links, Index,
CarleySoftware

OnBoard Diagnostic II (OBD II) HELP

Real information you can use to diagnose your car or truck

Copyright AA1Car.com

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The Malfunction Indicator Lamp (MIL) or CHECK ENGINE light as it is more commonly called, is essentially an emission
warning light. If the light comes on, it means the Onboard Diagnostics II system (OBD II) has detected an emissions-
related problem. OBD II is designed to turn on the MIL light if a problem occurs that may cause emissions to exceed
federal limits by 150 percent. The problem has to occur more than once, and it must be significant enough to create a
potential emissions problem (one serious enough to prevent a vehicle from passing an emissions test).




In the real world, the MIL lamp often comes on for what seems like trivia reasons (like a loose gas cap). But there's no
way to know what's triggering the light until the vehicle is diagnosed. The problem may be something minor that has little
or no effect on driveability, or it may be something more serious that is affecting engine performance.

The mysterious nature of the MIL lamp, which most people call the "Check Engine" light, terrifies and confuses a lot of
motorists. Except for a few luxury vehicles that actually display a fault message when the MIL lamp comes on, most

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provide no information whatsoever other than something is wrong. The motorist has no way of knowing if the problem is
major or minor -- or what it will ultimately cost to have the problem diagnosed and repaired.

Some motorists, on the other hand, seem unfazed by warming lights. As long as their vehicle continues to run, they see
no urgency to have their engine checked, to slow down or to do anything out of the ordinary. Others are optimists and
hope that if they keep on driving, the light will magically go out. Sometimes it does, much to their relief. But when the light
refuses to go out, or it comes and goes like the ups and downs of the stock market, they panic and don't know what to do.

Some motorists who are befuddled by a Check Engine light will seek out the least painful (and cheapest) solution which is
to take their vehicle to an auto parts store that offers a "free diagnosis." The diagnosis consists of plugging in a code
reader into the DCL connector and reading out the code. The auto parts stores who offer a free diagnosis service say the
code will usually reveal the nature of the problem so the motorist can decide what to do next. They're hoping, of course,
that the motorist will buy a part from their store and install it themselves to fix their problem. And if that doesn't work, that
the motorist will buy another part and install that in hopes it will solve the problem. And when that doesn't work, that the
motorist will buy yet another part and install it themselves in hopes of fixing he problem. You get the picture.

Anyone who repairs late model vehicles today for a living knows that diagnosing complex emissions and driveability
problems is not as simple as reading a code and replacing a part. OBD II is a great system that has a tremendous
amount of self-diagnostic capability, but it only identifies faults in particular circuits or systems. It does not tell you which
component to replace. That can only be determined after doing additional diagnostic work to isolate the fault.

Some problems such as misfires and evaporative emission (EVAP) leaks can be very challenging to nail down. Misfires
can be caused by ignition problems, fuel problems or compression problems. The underlying cause might be fouled spark
plugs, bad plug wires, a weak ignition coil, dirty injectors, a shorted or open injector, low fuel pressure, a vacuum leak, a
leaky head gasket, burned exhaust valve or a camshaft with a bad lobe. No simple plug-in diagnosis will give you the
answer until you do a lot of other checks.

To make matters worse, some of these friendly auto parts stores will also erase the code(s) after they've given their
customer the diagnosis. Erasing the code turns out the MIL light -- at least temporarily -- which provides some relief for
the poor motorist. But it may also make the job of diagnosing the fault harder if valuable diagnostic information that you
might have needed was erased.

OBD II & EMISSIONS TESTING

Another diagnostic issue that's becoming more of an issue with OBD II is that a growing list of states are now
substituting an OBD II emissions test for a tailpipe test. The OBD II test is quick and easy, goes not require an expensive
dyno or emissions analyzer, and gives a pass/fail indication in a minute or less. There's no risk of damage to the vehicle
(as may be the case when running a vehicle on a dyno), and the reliability of the OBD II test is actually better than a
tailpipe emissions test. Why? Because the OBD II system monitors emissions 24/7 365 days a year. There are no
arbitrary cutpoints that can be fudged one way or the other to pass or fail more or less vehicles. Everybody dances to the
same tune and must meet the same standards.

OBD II is also much better at detecting evaporative emissions leaks, and a drop off in converter efficiency. If the MIL light
is on and there's a code for an EVAP or converter problem, you can usually bet the problem is real. The problem may not
have any noticeable effect on driveability or performance, but technically it is in violation of the standards -- and must be
fixed before the MIL light will go out and say out.

OBD II monitors evaporative emissions by checking for fuel vapor leaks once a drive cycle. OBD II does this by applying
vacuum or pressure to the fuel tank, vapor lines and charcoal canister. If it detects no airflow when the EVAP canister
purge valve is opened, or it detects a leakage rate that is greater than that which would pass through a hole 0.040 inches
in diameter (0.020 inches for 2000 and up model year vehicles), it indicates a fault.

If you find a P0440 code that indicates a fuel vapor leak, finding the leak can be a challenge. The first place to start is the
gas cap. A loose-fitting or damaged cap can allow enough air leakage to set a code. To find a leak in a vapor hose, you
may need a leak detector that uses smoke and/or dye. A 0.020 inch hole is the size of a pin.

PLUG-IN DIAGNOSTICS

Page 95

OBD II for L & MD Vehicles OBD II for L & MD Vehicles
STD ManualSTD Manual

CLASS B Data Communications Network Interface CLASS B Data Communications Network Interface -- SAE J 1850:SAE J 1850:

Although this standard focuses on the physical, and data link laAlthough this standard focuses on the physical, and data link layers in the OSI model, the yers in the OSI model, the
application layer is also described since this needs to be incluapplication layer is also described since this needs to be included for emissionded for emission--related, related,
diagnostic communication legislation requirements. The class B diagnostic communication legislation requirements. The class B network maps into the OSI network maps into the OSI
model as illustrated in Figure 1 of the standard. The standard dmodel as illustrated in Figure 1 of the standard. The standard describes in detail the data link escribes in detail the data link
layer’slayer’s diagnostic messages, their formats, physical addressing of the diagnostic messages, their formats, physical addressing of the devices, bus protocol devices, bus protocol
commands, error detection and correction schemes. The physical dcommands, error detection and correction schemes. The physical dimensions of the network imensions of the network
and its electrical characteristics are described in detail. and its electrical characteristics are described in detail.

Appendix A lists the applicationAppendix A lists the application--specific features. Appendix B defines the I/O EMC test plan specific features. Appendix B defines the I/O EMC test plan
for the electro magnetic compatibility test to regulate electricfor the electro magnetic compatibility test to regulate electrical noise of the data signals. al noise of the data signals.
Appendix C gives the VPW wave form analysis that specifies the dAppendix C gives the VPW wave form analysis that specifies the data signal wave form ata signal wave form
characteristics for the 10.4characteristics for the 10.4 KbpKbp/s version. Appendix D gives the PWM wave form analysis that /s version. Appendix D gives the PWM wave form analysis that
specifies the data signal wave form characteristics for the 41.6specifies the data signal wave form characteristics for the 41.6 KbpKbp/s version./s version.
SAE J 1850 is the most important standard in the Data CommunicatSAE J 1850 is the most important standard in the Data Communication phase of the OBD II.ion phase of the OBD II.

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OBD II for L & MD Vehicles OBD II for L & MD Vehicles
STD ManualSTD Manual

Class B Data Communication Network MessagesClass B Data Communication Network Messages-- Detailed Header Formats and Physical Detailed Header Formats and Physical
Address Segments: (SAE J 2178/1): Address Segments: (SAE J 2178/1):

SAE J 2178/1, is the Class B Data Communication Network MessageSAE J 2178/1, is the Class B Data Communication Network Messages’ Detailed Header formats s’ Detailed Header formats
and Physical Address Assignments specification. The standard defand Physical Address Assignments specification. The standard defines the information ines the information
contained in the header and data fields of noncontained in the header and data fields of non--diagnostic messages. The standard also specifies diagnostic messages. The standard also specifies
field sizes, scaling, representations, and data positions used field sizes, scaling, representations, and data positions used within messages. The general within messages. The general
structure of the message frame is described withstructure of the message frame is described with inframeinframe response included in Figure 1 and response included in Figure 1 and
without the response in Figure 2 of the standard. without the response in Figure 2 of the standard. SAE J 1979SAE J 1979 standard defines the information standard defines the information
contained in the header and data fields of contained in the header and data fields of emission related diagnostic messagesemission related diagnostic messages. . SAE J 2190SAE J 2190
standard defines the information contained in the header and datstandard defines the information contained in the header and data fields of a fields of other diagnostic other diagnostic
messagesmessages not related to emissions. SAE J 1850 standard defines the classnot related to emissions. SAE J 1850 standard defines the class B network interface B network interface
hardware, basic protocol definition, the electrical specificatiohardware, basic protocol definition, the electrical specifications, and the error detectionns, and the error detection--
correction scheme using CRC (cyclic redundancy check) Byte. SAE correction scheme using CRC (cyclic redundancy check) Byte. SAE J 1850 defines only two J 1850 defines only two
message formats. They are the single Byte format and the consolimessage formats. They are the single Byte format and the consolidated header format. The dated header format. The
consolidated header format has two forms: a single Byte form, anconsolidated header format has two forms: a single Byte form, and a three byte form. This d a three byte form. This
standard covers all these formats and forms to identify the constandard covers all these formats and forms to identify the contents of messages which can be tents of messages which can be
sent on the SAE J 1850 network.sent on the SAE J 1850 network.

Page 190

Functionality ofFunctionality of PowertrainPowertrain
Control Module (PCM) in Control Module (PCM) in
OBD II DiagnosticsOBD II Diagnostics

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions
and meet OBD II regulations.and meet OBD II regulations.

Secondary Air management (contd): The first solenoid valve switches air flow to the
air cleaner or to the exhaust system. The second solenoid valve switches air flow either
to the exhaust manifold or to the catalytic converter. The PCM controls the air flow
depending on the engine coolant temperature, and Air/Fuel ratio which is not
stoichiometric ratio in this mode, which is open-loop control.

Evaporative Emission Canister Purge: The PCM releases the collected fuel
fuel vapors in the canister into the intake manifold via a solenoid controlled purge
valve periodically, during closed loop operation. This will simplify fuel calculation
during open-loop control.

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Functionality ofFunctionality of PowertrainPowertrain
Control Module (PCM) in Control Module (PCM) in
OBD II DiagnosticsOBD II Diagnostics

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions
and meet OBD II regulations.and meet OBD II regulations.

Automatic system Adjustment:: The PCM during closed-loop mode of control
checks the open-loop calculated air/fuel ratios and compares them with
closed-loop average limit values which are the ideal values for minimum
emissions. If the difference is large, the PCM corrects the open-loop lookup
table values so that the open-loop values are in close agreement with the
closed-loop values. This updated open-loop lookup table is stored in
non-volatile RAM memory. When the engine is started next time the PCM
uses the new lookup values which are closer to the stoichiometric ratio.
This feature is important since it enables the PCM to adjust to long-term changes
in engine and fuel system conditions due to wear and usage. This is similar
to fuel trim algorithm for fuel injection control.
These are all the PCM control functions performed to reduce emissions
and comply with OBD II requirements.

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