How to Get Check Engine Light Codes

On board diagnostics (OBD) was implemented in most vehicles in the early 1980s, although the 1975 Datsun 280Z was one of the first vehicles to use it. The idea was to make the vehicles communicate a problem in the emissions systems. Because of the lack of standardization, the OBD implementation was unsuccessful. A check engine light (also known as a malfunction indicator light, or MIL) would illuminate, but nothing standardized could be determined as to why. By 1996, OBD II was introduced on all vehicles sold within the United States. OBD II used a universal diagnostic link connector (DLC) to plug a device into and determine the cause of the check engine, or MIL, light displayed on the dashboard during operation.


  •  Things you will need A) Locate the OBD plug
  • B) OBD II code reader (for vehicles 1996 and up)
  • C) Trouble code chart(
    • 1
      Locate the diagnostic link connector in the vehicle. Vehicles manufactured with OBD (prior to 1996) will have the connector in the engine compartment (with the word "diagnostics" stamped on the cover). Refer to the owner's manual for the correct location. OBD diagnostic connectors were manufactured differently by various companies, so to connect to the link would require a plug specific for that make. OBD II vehicles (1996 and up) will have the DLCs located in the cabin of the vehicle, most likely under the driver's side dash. There is no universal position to place the DLC under the dashboard, and some manufacturers, like Honda, placed them behind the ashtray. Again, refer to the owner's manual for the correct location. OBD II DLCs are all universally shaped, which means any OBD II code reader or scan tool can plug into it no matter what company manufactured the vehicle.
    • 2
      Plug the code reader into the DLC of the vehicle. For OBD II, locate the correct adapter to plug into the diagnostic link and then plug the adapter into the scan tool.
    • 3
      Turn the ignition key two clicks in the ignition. This should be the accessory position (also known as key-on/engine-off) which provides power to the electrical system without the engine running.
    • 4
      Follow the instructions on the scan tool or code reader. Each device may ask for information such as certain vehicle identification numbers and engine size. Enter the information by scrolling through the options and pressing the "Enter" key on the face of the scan tool or code reader. Most new code readers for OBD II will jump right to reading and DTCs as the code reader obtains all the information it needs simply by plugging into the DLC and communicating with the vehicle.
    • 5
      Write down the trouble code displayed by the scan tool or code reader and refer to a trouble code chart (specific vehicle repair manuals often have trouble code charts) to determine the problem. As mentioned earlier, OBD diagnostics do not always pinpoint a specific problem, which is why OBD II was implemented. But even some OBD II trouble codes can require some troubleshooting and thorough diagnosing to determine the cause of the DTC.

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