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An OBDII Interface For A Laptop Computer

If you have a laptop PC you can build your own OBDII interface so you can access all the information available to a dedicated hand-held scan tool but at a much lower cost. Not only can you access all the fault codes in your car's ECU but you can then store them in your laptop for future reference.

Design by John Clarke

OBDII Interpreter: Main Features

• Enables checking for diagnostic trouble codes

• Clears trouble codes and Malfuntioning Indicator Lamp (MIL)

• Shows real-time data

• Extra features are software dependent

• Interpreter interfaces between the vehicle’s OBDII port and a computer

• Serial or USB connection (via an adaptor) to computer

• Power for the OBDII Interpreter obtained via the vehicle’s OBDII port

• Works with CAN, ISO, KPW, PWM and VPW protocols

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.

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