How to Read a Car Computer

by Allen Douglas

United States law requires that all vehicles of model year 1996 and newer sold in the U.S. be OBD-II-compliant. OBD stands for On-Board Diagnostic; these vehicles all have a data link connector providing a way to access the on-board diagnostic computer system. The car's computer provides valuable diagnostic information regarding many problems the car might experience. Any time the computer detects an issue, it logs all of the sensor readings at the time of detection. This data provides useful information for evaluating the vehicle's performance.

Find the OBDII data link connector (DLC). Look for the DLC under the dash of the driver's side of the vehicle. The connector will have a minimum of 16 pins. Some manufacturers' DLC ports have more than 16 pins.

Get a cable that connects from a OBD-II DLC to a computer. Several different manufacturers make cables for this purpose. Make sure that the computer side of the connector allows connection through a USB port.

Plug in the cable into the DLC. Use the first 16 pins open on the data link connector.

Install software to read the car computer. There are several different programs that read OBD-II compliant computers. Some OBD-II software is available for free, such as ScanMaster ELM and OBD Gauge. There are also more complete commercial ODB-II software titles available for purchase.

Plug the other end of the cable into your computer's USB port. Since the computer will need to connect to the data link connector, a laptop computer usually works best.

Use the software to read the car computer. Each OBD-II software title is slightly different regarding how to start the process of reading the car's on-board computer. Read the software directions before getting started.


  • check Most of the free software will only scan the computer codes and report basic information. The commercial software available for purchase typically provides more diagnostic tools, offering users enough information to identify engine problems.

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About the Author

Allen Douglas has been a techical writer for major scientific and engineering companies for 20 years. He writes articles specializing in technical topics on eHow. He holds a Master of Science in engineering from the University of Toledo and has practiced as a professional engineer in the Midwest and Southern United States.

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