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FAQ:About OBD-II

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  • FAQ:About OBD-II

    What is OBD-II?

    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.


    Where'd it come from?

    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.

    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.

    At first there were few standards and each manufacturer had their own systems and signals. In 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.


    Why do we need it?

    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.


    Does my car have OBD-II?

    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.

    There are three 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. GM cars and light trucks use SAE J1850 VPW (Variable Pulse Width Modulation), and Fords use SAE J1850 PWM (Pulse Width Modulation) communication patterns.

    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. 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.

    While there are three OBD-II electrical connection protocols, the command set is fixed according to the SAE J1979 standard.


    How do we measure OBD-II output?

    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 or a Palm PDA versions. 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.


    What good does it do to measure OBD-II output?

    OBD-II signals are most often sought in response to a "Check Engine Light" appearing on the 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.


    Tell me about that "Check Engine Light".

    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.

    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.


    OBD-II and your car's health

    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.

    Scanners vary greatly in their complexity. The best connect easily and use software to quickly and automatically call up the OBD-II information. They should have recording ability so that data can be collected during a test drive without distracting the technician driving the car. A system connecting to a laptop or desk top computer provides expanded memory for data and the ability to export data to a spreadsheet or graphing utility.


    Proprietary Sensor Readings

    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.


    OBD-II and performance tuning

    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.

    Adapted from http://www.obdii.com/background.html

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    Originally posted by bgoodman
    We're an international forum, post in whatever langauge you like.

  • #2
    Also of interest:
    http://en.wikipedia.org/wiki/OBD-II
    Chrysler 300 - Fabricating
    http://hallert.net/

    Comment


    • #3
      Thanks for the FAQ! Added to the FAQ of FAQ's.
      Originally posted by ghettocruzer
      I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
      Want to:
      -Find out about the new iBug iPad install?
      -Find out about carPC's in just 5 minutes? View the Car PC 101 video

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      • #4
        Where do we get the cable and software and what do these parts roughly cost?
        1999 Black Pontiac Trans Am
        CarPC's in F-bodies
        How To Relocate Climate Controls on the 97-02 F-body Cars
        (AMD Sempron 3000+, Opus 150)
        Car PC system is out, Alpine system is in.

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        • #5
          Suppliers of OBDII hardware:

          1. Digimoto
          2. Scantool
          3. Ross-Tech (VW/Audi specific)
          4. Autotap
          Originally posted by ghettocruzer
          I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
          Want to:
          -Find out about the new iBug iPad install?
          -Find out about carPC's in just 5 minutes? View the Car PC 101 video

          Comment


          • #6
            Can the OBD-II be used to control your windows, heater, a/c and other controls like that???
            Trying is the first step toward failure

            Comment


            • #7
              Originally posted by canadapettit
              Can the OBD-II be used to control your windows, heater, a/c and other controls like that???
              No
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              • #8
                Thanks for the short answer. Then what can you get to control that???
                Trying is the first step toward failure

                Comment


                • #9
                  relays and a ton of serial ports with custom software to boot. Back to OBD FAQ
                  mp3Car.com Senior Tech Blogger (Want a product reviewed? Contact me.)
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                  • #10
                    Originally posted by canadapettit
                    Thanks for the short answer. Then what can you get to control that???
                    Are all power windows/doorlock/hvac switches/buttons broken? Does your car has power windows/doorlock?
                    And I hope you still have 10 fingers on your hands to punch/push/turn those buttons/knobs.


                    If you mean to control it via computer, yes, there are relay cards. Read up the hardware development forum.
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                    • #11
                      All of the HAVC control are all electric i was just curious as to how a carputer could control all of them and could it be done
                      Trying is the first step toward failure

                      Comment


                      • #12
                        Originally posted by canadapettit
                        All of the HAVC control are all electric i was just curious as to how a carputer could control all of them and could it be done
                        Depending on the vehicle the system can operate in several ways.

                        -The most common is vacuum-assisted moduation where the knobs are vacuum chambers and merely direct a vacuum charge from area to area to determine which way the air travels.
                        -Electronic systems use a variety of switch and control the flapper doors by small servo/motors.
                        -The least common way which I dont even know if it is in practice is operational over the I-bus and uses the automatic climate control systems and makes adjustments through the ECU. This would work and is theoretically a great way to further integrate older systems into a new and more elegant system but I dont know of any examples utilizing it.

                        Now as far as controlling a system via carPC, its possible but it would require being completely custom to each application and would need some little bits and pieces and some coding. I am currently working on the idea with vacuum solenoids and electronic modulation via a serial port. I unfortunately dont have a car fitting to install the system in but as soon as I allocate a 300zx I plan to begin work.

                        ~Kris
                        [1995 Nissan 240sx]

                        Planning.........[::::::::::] 90%
                        Parts.............[::::::::::] 60%
                        Construction...[::::::::::] 10%
                        Software........[::::::::::] 50%

                        [1994 Mazda RX-7]

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                        • #13
                          Check Maestro's thread on HVAC before working on this too much!
                          Originally posted by ghettocruzer
                          I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
                          Want to:
                          -Find out about the new iBug iPad install?
                          -Find out about carPC's in just 5 minutes? View the Car PC 101 video

                          Comment


                          • #14
                            Originally posted by Bugbyte
                            Check Maestro's thread on HVAC before working on this too much!
                            That is quite impressive, although it saddens me to think I wasnt innovative or original in my thought process for the idea. lol

                            Although I see some flaws in his system. Particularly that of cars already equiped with an automatic climate control system. The other flaw is working with a vacuum-based flapper control car... although it seems his design requires removal of the dash to replace the vacuum/electrical doors with R/C servos. My plan is to use all the OEM equipement, only modifying the electrical front-end and interfacing it with a VB visual 'dash' on the PC.

                            ~Kris
                            [1995 Nissan 240sx]

                            Planning.........[::::::::::] 90%
                            Parts.............[::::::::::] 60%
                            Construction...[::::::::::] 10%
                            Software........[::::::::::] 50%

                            [1994 Mazda RX-7]

                            Comment


                            • #15
                              Originally posted by Sonicxtacy02
                              No
                              Not trying to steer this off OBDII, but I thought some of the new cars were sending that stuff over the CAN-Bus?

                              As an aside, my car (a 2002) uses a proprietary signaling system that's more or less I2C (called SWS) for everything (lights,switches,buttons) except HVAC.
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