Welcome to the OBDII Automotive Diagnostics Page

NEW information and updates:

June 14, 2005
Windows software (version 3.0) available
Click here for details or to download.

Frequently Asked Questions. This page may have a quick answer to your question.

Description:

This is an interface between a personal computer and a vehicle's OBDII diagnostic bus. It allows you to Read out trouble codes when your "check engine" light comes on. You can also clear these codes. You can retrieve pretty much any piece of OBDII mandated diagnostic data from your vehicle. The interface supports OBDII protocols commonly used in US vehicles: VPW (General Motors), PWM (Ford), and ISO9141 (Chrysler, Asian, and European), and ISO 14230 protocol (also called Keyword 2000).
It does not support the CAN interface. A few newer vehicles use the CAN interface (check Equipment and Tool Institute http://etools.org for a listing).

Note: In general, it will not work on OBD-1 vehicles or any vehicles earlier than 1996 models. (There are a very few vehicles with OBDII systems before 1996. GM vehicles before 1996 are not compatible.)

The following is a list of data that you can monitor with this interface. Note that a given vehicle may not support some of the data items.

MODE 1: Status of onboard tests , Fuel system status, Engine load, Coolant temperature, Fuel Trim (Long and short term), Manifold Pressure, Engine Rpm, Vehicle speed, Ignition timing advance, Intake air temperature, Intake air flow rate, Throttle position, Secondary air status, Oxygen sensor locations, Oxygen sensor voltages, and there are also a few others. Some data items may not be supported by a given vehicle.
MODE 2: This mode retrieves data that is similar to mode 1 above, but it was stored as a "Freeze frame" at the instant that the vehicle discovered a problem and set a diagnostic trouble code (DTC). Not all of the mode 1 variables are included in mode 2.
MODE 3: Reports Powertrain diagnostic trouble codes ("P" codes), including manufacturer specific codes which are reported under this mode.
MODE 4: Clears diagnostic trouble codes. It also clears the result of continuously and non-continuously monitored on board test results (modes 5 and 6), as well as freeze frame data.
MODE 5: Reports On board Oxygen sensor test results.
Some vehicles perform background diagnostics on the various oxygen sensors and this mode reports the results. Some of them are generic, but SAE also included provisions for manufacturer specific tests. Some vehicles use mode 6 to report these results.
MODE 6: Reports On board (non-continuously monitored) test results. This mode reports the results of various tests that the vehicle has performed. The interface will report any available data and format it in the SAE defined method, but many of these tests are manufacturer specific, so our PC software cannot interpret them for a specific vehicle. It will display the test value, and the upper and/or lower limit that the vehicle reports.
MODE 7: Reports On board monitoring results for continuously monitored systems. These are basically similar to mode 3 trouble codes, but they are set after a single driving cycle. They are useful to see if the vehicle has detected any problems after repairs have been made.
MODE 9: Mode 9 reports various data such as the vehicle's VIN number and calibration data. The current software attempts to retrieve the VIN number, but other functions appear to be manufacturer specific and are not querried.

The Host PC Programs:

Programs have been written to run on a PC and communicate with the interface. These programs run on just about any PC with a serial port. [There are a few PCs that only have USB, but you can probably use a USB/serial convertor cable] These programs also run in a "simulated" mode even if there is no interface or vehicle attached. This allows you to examine the program or learn how it works. The programs are free, and they are full versions, not Demos; they will work with the inteface.

These programs only work with a BR interface, and do not support other interfaces. Similarly, most other software does not currently support the BR interface, but if any others become available, they will be linked below for your convenience.

Description, Downloads, Screenshots :

DOS program

Windows Version.

Links to Software from other sources:
(Keep in mind that these programs are either unsupported, or supported by their authors)

LINUX - FreeDiag Software for Linux users, including source C code.

APPLE / MAC Users: We do not have a native MAC program, but it may be possible to run our windows programs under an emulator on some MACs. This user has reported success, and has put some instructions on the net that may possibly guide you. Click HERE to go to that web page.

Ordering Items

Here, you can find ordering information for complete and ready to use interfaces, chips, boards, and other accesories that may be of interest.

Order information Page

Technical Information

This section provides information only useful to those who are building their own hardware.

Electronic hardware

Schematic Diagram
Download Data sheet (pdf, 103 kb)
Circuit notes (Text file) Be sure to read this if you are building your own circuit.

Software Information

Programer's data

General Information

If you have a question please read the FAQ before you inquire.