How to Use a Fault Code Reader

Written by bob white
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How to Use a Fault Code Reader
A fault code reader quickly narrows down the problem with your automobile. (Jupiterimages/ Images)

A fault code reader assists you in repairing your car by telling you what the vehicle's self-diagnostic system "thinks" is wrong. Since 1996, Federal law requires that all vehicles sold in the United States be on-board diagnostic (OBD) compliant. The standard in 2011 is OBD2 and is an improvement on the original system. When a fault code enters the vehicle's computer it triggers the check engine light. By understanding that code, you can quickly narrow down the problem and make your repair.

Skill level:
Moderately Easy


  1. 1

    Turn the vehicle's ignition to the off position.

  2. 2

    Locate the vehicle's 16-pin data link connector. This looks similar to a computer serial port and is typically located under the dashboard below the steering wheel or on the left, bottom corner.

  3. 3

    Push the code reader's cable connector into the vehicle's data link connector. Be careful to properly align the connections to avoid damaging the pins.

  4. 4

    Look at the OBD2 code reader to see if it automatically turned on when you plugged it into the vehicle. If it did not you may have a problem with a blown fuse. Check your fuse panel and replace any blown fuses.

  5. 5

    Turn the vehicle's ignition to the on position but do not start the vehicle. The fault code reader will automatically check the vehicle's computer for fault codes.

  6. 6

    Wait 10 to 60 seconds for the fault code reader to download the codes. The codes will be displayed on the screen with an explanation of the problem. If there is more than one code on the vehicle's computer, you can cycle through them by pressing the button with an arrow pointing to the right.

  7. 7

    Record the fault codes on a note pad for reference when working on the car.

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