OBDII Automotive Diagnostics and serial port connections

8th Friday, 2012  |  Engineering News, Life at LAVA  |  no comments

Vehicles manufactured after 1996 have a capability that few drivers realize exists: your vehicle has an interface to its computer that can provide a panoply of information about your vehicle’s operation and status, second by second. This interface, the On-Board Diagnostics (OBD) port, gives information on speed, acceleration, fuel use, temperatures (of oil, coolant, air intake, etc,), engine load, rpms, electrical voltages, fault conditions, and much more. If you’ve ever had your “Check Engine” light go on, and not known why, this interface will tell you precisely why, as well as making it possible to reset the indicator. Those skilled in tuning their cars’ engines use OBDII as a matter of course.

The current incarnation of the standard, OBDII, works with almost all cars on the market in one form or another. The OBDII output coming from the car’s electronics feeds into a computer running software to interpret and display this data, or to a piece of dedicated automotive troubleshooting hardware.

Typical OBDII-to-RS-232 interface cable

Typical OBDII-to-RS-232 interface cable

When connecting OBDII outupts to a computer, a number of OBDII connectors will do the job: OBDII-to-RS-232 serial, OBDII-to USB, OBDII-to-WiFI, and OBDII-to_Bluetooth, among others. For ODBII devices addressing outputs to RS-232 serial , LAVA has a number of RS-232 serial interface ports that will do the job. For desktop PCs, any one of a number of our PCI and PCIe serial port cards are great. If you have a laptop, our USB-to-Serial Link will work very well.


A good general introduction to OBDII:

The OBDII specification is not publicly available, but a lot of information is at:

A variety of OBDII interface methodologies:

Some typical OBDII-to-RS232 interfaces:

For the hobbyist interested in building their own OBDII-to-RS-232 interface:

A good site for determining OBDII compatibility for “transitional” 1995/1996 vehicles:

For those interested in interfacing the ELM327 to RS232 in Linux:

Much of the OBDII interfacing uses the ELM327 interpreter chip. This chip provides an RS-232 (serial) interface to ODBII data. The gamut of ELM327 chips and their specifications are here:

For those interested in looking deeper in to OBDII, or interested in making their own interface hardware: