How to Read OBD2 Codes

Knowing how to read OBD2 codes can save you a lot of money. OBD2 codes are alphanumeric codes that are generated by the on-board diagnostic system when it detects a possible problem and are stored in its memory; you can read these codes by using a code reader that you will connect to your car’s data link connection.  By using the codes to determine the general nature of a problem your car may be suffering, you can decide if you’re capable of fixing it yourself or have to take it to a mechanic.

The Basics of OBD2 Codes

obd2 codes

OBD2 codes have five characters. The first character indicates which system may be having problems, and can be:

  • P – Powertrain
  • B – Body
  • C – Chassis
  • U – Undefined

Of these four, you’re most likely to encounter P most often in OBD2 codes since the power-train is where most problems commonly lie.

The next digit in the codes can be either 0 or 1, which tells you if it is a generic code common to all OBD-II equipped vehicles, or a proprietary code that is specific to a particular car maker.

The third digit of OBD2 codes will identify which sub-system may be experiencing problems:

  • 1 – Fuel or Air Emission Management
  • 2 – Fuel or Air Injector Circuit
  • 3 – Ignition or Misfire
  • 4 – Emission Control
  • 5 – Vehicle Speed/Idle Control
  • 6 – Computer and Output Circuit
  • 7/8 – Transmission
  • 9/0  – SAE reserved

The fourth and fifth digits of the code will pinpoint the specific area where a scanner has detected a problem.  To illustrate: If your code reader displays the trouble code P0299, it means that there is a problem in the power-train system, in the injector circuit and there is an issue related to the pressure of your engine turbo supercharger. Note that the diagnostic codes only indicate there is a problem in a particular system, not what’s causing it. You will have to either determine that for yourself or ask a technician to diagnose the cause.

How to Use OBD2 Codes to Diagnose a Problem

 

To illustrate how these codes can be used to pinpoint a problem with your car, let us use the above code P0299. If your code reader displays this code, it could indicate that the two parts of your turbo housing resonator have started to separate, affecting the turbo pressure of your car. If you have a European model, however, it may mean that the waste gate solenoid activator is broken, causing the engine to lose power due to turbo inactivity. There are many websites that list the generic diagnostic codes as well as those specific to manufacturers that you can look up to determine what the code means and what it may indicate.

Note that once the problem has been fixed, you will have to delete the code to verify that it has genuinely been repaired. Once you delete old OBD2 codes new ones will appear if there are further problems; note, however, that all other data stored in the system’s memory will also be erased and it will begin recollecting data as soon as you drive the car again.

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