Elsewhere in this issue, we have a major feature on the topic of On-Board Diagnostics (OBDII) and here we describe how to build your own OBDII scan tool. If you are not familiar with OBDII, then you should read the feature article before reading further about this project.

Hand-held OBDII scan tools are very convenient, especially where they can be used everyday in a car workshop. However, for the home mechanic, the cost of a hand-held unit may not be justified, especially when it might only be used occasionally.

While this OBDII Interpreter does have an obvious drawback in that you must use it with a laptop computer, it does duplicate all the features available in a hand-held scan tool using freely-available software.

Alternatively, for those who have a Palm computer or a Pocket PC2002 or 2003 with a serial port, there is software available that allows these units to be used as an OBDII scan tool instead of a standard PC. We have not tried the software for the Palm or Pocket PC but we expect that it will work as claimed by the software vendors.

For the PC, there are several free software programs that are suitable for computers running Windows 98 through to Vista. We tried three of these software programs on a laptop running Windows XP with success.

The SILICON CHIP OBDII-to-RS232 Interpreter enables your laptop PC, Palm etc to operate with OBDII protocols including CAN, ISO, KPW, PWM and VPW. The Interpreter converts the signals from OBDII format to a form suited to communication with a PC.