Engine fault light displayed on dashboard

How to diagnose car error codes with OBD 2?

If an error light displayed on the dashboard and you are looking to self-diagnose or maybe just to gain a little bit better understanding of what may have caused it before taking the vehicle to a technician please read on. In a world where technology is widely available and most of us are familiar with smartphones, using an OBD reader should not be too difficult.

What is OBD?

On-Board Diagnostics (OBD) is a term used for a vehicle's reporting capability to help diagnose faults. OBD-II is an improved version of OBD that standardizes the connector pin layout and messaging protocol and provides data access from the ECU (Engine Control Unit). More detailed information on what OBD is can be found online easily (e.g. Wikipedia), but what's important for us is how we can utilise it.

How to get one?

First of all we recommend buying an OBD-II reader from a trusted retailer, but before doing so ensure your vehicle does have an OBD-II port (all modern vehicles should do). Having one of these little gadgets are always handy and can certainly pay off. There is a variety available online in the price range of £10-£30.

White OBD port location on a 2006 Toyota Celica
White OBD port location on Toyota Celica
OBD-II reader connected
OBD-II reader connected

How to use it?

The OBD-II reader should come with instructions, but here is what you can expect:

  1. Download an OBD diagnostic software to your preferred device (e.g. smartphone or laptop)
  2. Plug the OBD-II reader into the vehicle's OBD socket
  3. Turn on the ignition
  4. Turn on the bluetooth on your device (smartphone)
  5. Pair your device with the reader
  6. Launch the downloaded OBD software
  7. Find the read fault code history section
  8. Research what the fault code means
OBD-II fault codes
OBD-II fault code reading

Free software is available to download that can read the vehicle's fault code history, paid software is likely to have more features that you probably will not need just to carry out basic diagnostics. Pairing will possibly require a PIN that is included in the OBD-II reader user manual. We found that some phone's bluetooth may not see the reader, in that case try another device/smartphone. Error codes can be manufacturer specific and an error code can mean various things, but they largely narrow down the possible causes of the problem. An experienced technician can probably tell the most likely cause of an error code. Some OBD software can also clear error codes, but obviously that does not fix their undelying issue and they will most certainly reappear soon.

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