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What are OBD2 Diagnostic Trouble Codes?

Whether you’re a hands-on car owner, a serious DIY-er or a professional mechanic, it is important that you know OBD2 Diagnostic Trouble Codes (DTC) and what they mean. 

In this article, we’ll take a dive into DTCs – the whats and hows. And we’ll also (try to) explain why it is important for you to be familiar with how to obtain and read these for your car’s health or to diagnose an issue..

What are Diagnostic Trouble Codes?

Cars produced from 2006+ onwards in Australia come equipped with the OBD2 system. With this, your car’s computer now can store data of errors that happened in your vehicle.

If an engine part, transmission, brake, or any sensor has a malfunction, the computer picks it up, alerts you (mainly through the Check Engine Light, or other check lights), and saves this data for extraction later. 

Before, you will know a fault in your car after it occurs (i.e. engine misfire, overheat, loss of brakes, among others). With OBD2 and DTCs, there is now a way to warn drivers of a potential catastrophic failure in any of the car’s multiple functional systems. 

Moreover, the benefits of diagnostic trouble codes goes beyond the safety aspect. Learning how to obtain and read these codes saves you hundreds of dollars in repair costs. When you can clean a clogged valve before it gets totally damaged means you don’t have to buy that expensive car part. You also assist your friendly, neighbourhood mechanic on locating immediately the faulty car part, saving you time in the repair shop.

A word of caution, though. Some codes are specific to a certain car brand. So when reading DTCs, be sure you’ve done your research and have consulted the car’s manual. If you’re unsure, it’s no shame to proceed to your trusted professional mechanic for help. 

How to read Diagnostic Trouble Codes?

OBD2 Diagnostic Trouble Codes guide

The Society of Automotive Engineers developed and standardised diagnostic trouble codes, and these have been adopted by all automotive manufacturers worldwide. And each of the five (5) characters in the code has its own meaning:

1st Character: MAIN CAR SYSTEM WITH FAULT

  • B-codes (body codes)

Refers to car parts inside the vehicle that deal with comfort, convenience, and safety.

  • C-codes (chassis codes)

Car functions outside the dashboard, including suspension, brakes, and steering.

  • U-codes (network and vehicle integration codes)

Features within the car’s system and computer

  • P-Codes (powertrain codes)

What makes the car move – engine, transmission, drivetrain.

2nd Character: GENERIC or MANUFACTURER-SPECIFIC

  • “0” – Generic/Global fault

These are codes standard for all manufactures and based on OBD2/EOBD standards. 

  • “1” – Manufacturer-specific/Enhanced fault

Codes set by manufacturers for functions or features unique to their vehicles.

Note: 

Powertrain CodesChassis CodesBody CodesNetwork Codes
P0xxx – GenericC0xxx – GenericC0xxx – GenericC0xxx – Generic
P1xxx – Manufacturer-specificC1xxx- Manufacturer-specificC1xxx – Manufacturer-specificC1xxx – Manufacturer-specific
P2xxx – GenericC2xxx – Manufacturer-specificC2xxx – Manufacturer-specificC2xxx – Manufacturer-specific
P30xx to P33xx – Manufacturer-specificC3xxx – GenericC3xxx – GenericC3xxx – Generic`
P34xx to P39xx – Generic

3rd Character: SPECIFIC CAR SYSTEM WITH FAULT

  • “1” – Fuel and Air Metering
  • “2” – Fuel and Air Metering (injector circuit)
  • “3” – Ignitions Systems or Misfire
  • “4” – Auxiliary Emission Control
  • “5” – Vehicle Speed Control and Idle Control Management
  • “6” – Onboard Computer and Ancillary Outputs
  • “7, 8, or 9” – Transmission (gearbox)
  • “A, B, or C” – for Hybrid Propulsion

4th and 5th Character: SPECIFIC DESCRIPTION AND PART WITH FAULT

  • Numbered as “00” and onwards

There are more than 5,000 identified diagnostic codes now. And with more car models and technology coming in, you can expect more DTCs to be created. It is therefore important to keep up to date on these developments.

How to get the Diagnostic Trouble Codes?

  1. The first thing you need is a reliable OBD2 diagnostic scan tool.
  1. Search for the OBD2 port of your vehicle. It is usually found on the bottom of the steering wheel or above the pedals, but it is a good idea to consult your car’s manual as the location differs for each car model.
OBD2 port
  1. Plug in the OBD2 scan tool. It may be an adapter cable or a dongle, depending on the tool you will use.
  1. Then, turn on the ignition, but do not start the engine. 
  1. Open the device, or the application on your phone or laptop. 
OBD2 Scan Tool
  1. Enter the Vehicle Identification Number (VIN), make, model, and engine number. Almost all existing scan tools have a database of majority of car models. You just need to scroll through the interface to look for your vehicle. If you are still unsure, consult your car’s manual, or you may ask your car dealer. 
  1. Search for the “Codes” or “Trouble Codes” option. The device will give you the existing trouble codes.
OBD2 Scan Tool App
  1. Time to interpret the codes using the steps we mentioned earlier. 

How to clear a Diagnostic Trouble Code?

You can also clear DTCs using the same OBD2 diagnostic scan tool you used to look obtain and read it. This is the easiest and safest way to do it. However, clearing this codes does not mean fixing the actual faults or malfunctions. You still need to find the cause of the error and fix it. 

Turning off the Check Engine Light can also be done using an OBD2 scan tool. But it will turn back on if the actual cause of the fault isn’t fixed or removed. 

Never try to clear trouble codes by unplugging the car battery. You’ll not just lose the trouble codes, but you might also lose critical car settings the vehicle computer has saved over time. 

Our Final Word

Having familiarity with OBD2 diagnostic trouble codes (i.e. how to obtain, read, and clear them) can benefit you as a driver in terms of maintaining a healthy vehicle and saving time and money on repairs and maintenance. 

Once your car’s check engine light turns on or the limp mode triggers, you now have the knowledge on how to diagnose and fix these problems. You might need a couple of tools, but you now know what to do. 

Still, monitoring DTCs should not only be done after a car problem occurs. Regular checks and maintenance of your vehicle is not something you should take for granted. 

As any doctor (including car doctors) would say: Prevention is better than cure!

For questions about diagnostic trouble codes (or anything about vehicles, really), we would be happy to help you answer them. Talk to us here!

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