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`OBD-II Background
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`What is OBD-II?
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`Where'd it come from?
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`Why do we need it?
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`Does my car have OBD-II?
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`How do we measure OBD-II output?
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`What good does it do to measure OBD-II output?
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`Tell me about that "Check Engine Light".
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`OBD-II and your car's health
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`Proprietary Sensor Readings
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`OBD-II and performance tuning
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`What is OBD-II?
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`On-Board Diagnostic systems are in most cars and light trucks on the road today. During the
`'70s and early 1980's manufacturers started using electronic means to control engine functions
`and diagnose engine problems. This was primarily to meet EPA emission standards. Through
`the years on-board diagnostic systems have become more sophisticated. OBD-II, a new
`standard introduced in the mid-'90s, provides almost complete engine control and also monitors
`parts of the chassis, body and accessory devices, as well as the diagnostic control network of
`the car.
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`Where'd it come from?
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`To combat its smog problem in the LA basin, the State of California started requiring emission
`control systems on 1966 model cars. The federal government extended these controls
`nationwide in 1968.
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`Congress passed the Clean Air Act in 1970 and established the Environmental Protection
`Agency (EPA). This started a series of graduated emission standards and requirements for
`maintenance of vehicles for extended periods of time. To meet these standards, manufacturers
`turned to electronically controlled fuel feed and ignition systems. Sensors measured engine
`performance and adjusted the systems to provide minimum pollution. These sensors were also
`accessed to provide early diagnostic assistance.
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`At first there were few standards and each manufacturer had their own systems and signals. In
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`1988, the Society of Automotive Engineers (SAE) set a standard connector plug and set of
`diagnostic test signals. The EPA adapted most of their standards from the SAE on-board
`diagnostic programs and recommendations. OBD-II is an expanded set of standards and
`practices developed by SAE and adopted by the EPA and CARB (California Air Resources
`Board) for implementation by January 1, 1996.
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`Why do we need it?
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`The Environmental Protection Agency has been charged with reducing "mobile emissions" from
`cars and trucks and given the power to require manufacturers to build cars which meet
`increasingly stiff emissions standards. The manufacturers must further maintain the emission
`standards of the cars for the useful life of the vehicle. OBD-II provides a universal inspection
`and diagnosis method to be sure the car is performing to OEM standards. While there is
`argument as to the exact standards and methodology employed, the fact is there is a need to
`reduce vehicle emitted pollution levels in our cities, and we have to live with these requirements.
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`Does my car have OBD-II?
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`All cars built since January 1, 1996 have OBD-II systems. Manufacturers started incorporating
`OBD-II in various models as early as 1994. Some early OBD-II cars were not 100% compliant.
`<Click here> to see the dates OBD-II started being included on specific makes and models.
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`There are five basic OBD-II protocols in use, each with minor variations on the communication
`pattern between the on-board diagnostic computer and the scanner console or tool. While there
`have been some manufacturer changes between protocols in the past few years, as a rule of
`thumb, Chrysler products and all European and most Asian imports use ISO 9141 circuitry or
`KWP2000. GM cars and light trucks use SAE J1850 VPW (Variable Pulse Width Modulation),
`and Fords use SAE J1850 PWM (Pulse Width Modulation) communication patterns. <Click
`here> to see which cars use each system. CAN is the newest protocol added to the OBD-II
`specification, and it is mandated for all 2008 and newer model years.
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`You may also tell which protocol is used on a specific automobile by examining the connector
`socket carefully. If the dash connector has a pin in the #7 position and no pin at #2 or #10, then
`the car has the ISO 9141 protocol or KWP2000. If no pin is present in the #7 position, the car
`uses an SAE protocol. If there are pins in positions #7 and #2 and/or #10, the car may use the
`ISO protocol. The CAN protocol uses pins #6 and #14.
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`While there are OBD-II electrical connection protocols, the command set is fixed according to
`the SAE J1979 standard.
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`How do we measure OBD-II output?
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`Pre-OBD-II cars had connectors in various positions under the dashboard and under the hood.
`All OBD-II cars have a connector located in the passenger compartment easily accessible from
`the driver's seat. Check under the dash or behind or near the ashtray. A cable is plugged into
`the OBD-II J1962 connector and connected to AutoTap or another scan tool. AutoTap is
`available in PC/laptop. Other scantools on the market range from simple hand-held meters that
`display trouble codes, up to a large console computer-based unit costing thousands of dollars.
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`What good does it do to measure OBD-II output?
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`OBD-II signals are most often sought in response to a "Check Engine Light" appearing on the
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`dashboard or driveability problems experienced with the vehicle. The data provided by OBD-II
`can often pinpoint the specific component that has malfunctioned, saving substantial time and
`cost compared to guess-and-replace repairs. Scanning OBD-II signals can also provide valuable
`information on the condition of a used car purchase.
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`Tell me about that "Check Engine Light".
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`The service industry calls the Check Engine light on your dash an "MIL" or Malfunction Indicator
`Light. It shows three different types of signals. Occasional flashes show momentary
`malfunctions. It stays on if the problem is of a more serious nature, affecting the emissions
`output or safety of the vehicle. A constantly flashing MIL is a sign of a major problem which can
`cause serious damage if the engine is not stopped immediately. In all cases a "freeze frame" of
`all sensor readings at the time is recorded in the central computer of the vehicle.
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`Hard failure signals caused by serious problems will cause the MIL to stay on any time the car
`is running until the problem is repaired and the MIL reset. Intermittent failures cause the MIL to
`light momentarily and they often go out before the problem is located. The freeze frame of the
`car's condition captured in the computer at the time of the malfunction can be very valuable in
`diagnosing these intermittent problems. However, in some cases if the car completes three
`driving cycles without a re-occurrence of the problem, the freeze frame will be erased.
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`OBD-II and your car's health
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`Because of their investment in the equipment required, most repair shops charge a fee, some-
`times substantial, to attach the scanning equipment and diagnose problems using the OBD-II
`system signals. Home mechanics and small shop technicians have been restricted from working
`with these signals by the cost and technical complexity of the equipment. With the introduction
`of more economical and user friendly scanning devices, it is now practical for almost anyone to
`access OBD-II signals and use them for their own testing and repairs.
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`Scanners vary greatly in their complexity. The best connect easily and use software to quickly
`and automatically call up the OBD-II information. A system connecting to a laptop or desktop
`computer provides expanded memory for data and a graphing utility.
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`Proprietary Sensor Readings
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`Though not part of the EPA's OBD II standard, the diagnostic read-outs used by dealership
`technicians are also read through the OBD II connector. These service codes show you such
`things as knock sensor operation, FI pulse width, ignition voltage, individual cylinder misfires,
`transmission shift points and ABS brake condition. There can be over 300 readings available,
`depending on the vehicle manufacturer and model. Vehicles vary in the readings they will
`support. Scanners vary widely in the number of these signals that they can read. Some show
`just the basic OBD or OBD II signals, others show the full range of service codes.
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`OBD-II and performance tuning
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`While the vast number of drivers want nothing more than dependable, economical
`transportation, many of us are looking to OBD-II for extra performance. Earlier on-board
`computer systems had chips that could be replaced to adjust engine parameters for extra speed
`and power. While the OBD-II systems are sealed and do not allow chip replacement, they do
`provide a real time data acquisition system that is useful to tuners.
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`Power loaders can actually reprogram the performance parameters of the OBD-II system to
`accommodate performance options. At the current time the number of models they can service
`is limited, but the range is being extended. Be sure the person doing your reprogramming keeps
`the car in compliance with EPA emission standards. As aftermarket manufacturers develop
`additional solutions, we will add their information to our links.
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`For information on the AutoTap OBDII scan tool, visit www.autotap.com.
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`[ OBD-II Home ]
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`The OBD-II Home Page is hosted by
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`© 2011 B&B Electronics
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