While computers were integrated in vehicles as early as 1969 (fuel-injected VWs), on-board diagnostics (OBD) were not mandated until the early 1980s. Because the beginning phase of OBD was vehicle specific, it complicated the procedure to read check engine codes. By 1996, the second phase of OBD was introduced. Known as OBD II, this phase standardized all vehicles sold in the United States to use the same data link connector (DLC), which was to be located within 12-inches from the steering column. This simplified the equipment needed to read and check the check engine codes on all cars.
Locate the DLC on your vehicle. If necessary, use the owner's manual to find its location. Most vehicles place it under the driver's side dashboard. It may have a small cover or it may be uncovered. There are some import vehicles (Honda) that place the DLC behind the ashtray.
Plug the OBD II scanner into the DLC. Because of the shape of the DLC and the plug of the scanner, you can only plug it in one way. The battery of the vehicle will provide power to most OBD II code readers, but if a power button is present, turn the button to on.
Turn the ignition key to the key-on/engine on position. This is normally two forward clicks in the ignition. This will illuminate all the lights on the instrument panel without the engine running.
Look at the onscreen menu of the code reader. While these code readers are now made by many different manufactures, operating them is very self-explanatory and easy.
Use the scroll button(s) to locate the "read codes" or the "read DTCs" (diagnostic trouble codes) option.
Press the "enter" or "send" key on the scanner. The scanner will read the DTC stored in the vehicle's computer. A four- to five-digit code will appear. The first digit is always a letter. The most common is P for powertrain; however, B codes (for body) and C codes (for chassis) may also appear. U codes are rare and usually indicate invalid or missing data. The next series of digits will be a specific number.
Look up the number on an OBD II website for more information on it. While many code readers will give a brief description of the code, many less expensive models will only show the DTC.
