DTC codes

Here's everything you need to know about DTC - OBD2 codes. What are they? How do you recognize them? What is their structure? How are they solved?

What is a DTC code?

When scanning the Engine Control Module (ECM), if the vehicle shows a fault, it will display a code. These codes are called DTC codes (Diagnostic Trouble Codes)

How is a DTC code structured?

The first value of the fault code will always be a letter. Depending on the area of ​​the vehicle where the fault is located, a different letter will appear. The letters that appear are the following:

  • P = Powertrain: Fault codes that begin with the letter ‘P’ imply that the fault comes from the drive train, that is, comes from the automatic transmission or the engine.
  • B = Body: When the code begins with the letter 'B', it means that the fault is in the body of the vehicle.
  • U = Network: If the code has a 'U' at the beginning, then the failure has to do with the system of data transmission between the different modules that are located in the vehicle. This can be dangerous, since with the malfunction of a module, an entire system can disappear from the diagnostic system. In this case, the remaining functional modules show this type of failure.
  • C = Chassis: Now, if it is a 'C', it implies that the fault is located in the chassis, such as air bags, brakes, etc.

The second value will always be a number. This value is what determines whether the code is universal (ie, it means the same in any car, these codes are easier to diagnose and repair) or if it is a code developed by the manufacturer.

The number '0' indicates that the code is totally generic (universal), while numbers 1, 2 and 3 indicate that it is a code made by the manufacturer, although it does not obviate the fact that it remains OBD-II (below) we will explain what this protocol is).

The third value will also be a number. This digit will tell us more precisely where the fault comes from.

1 = Failure caused by a malfunction of a sensor located in a system that controls the air-fuel ratio in the engine, or any other factor that influences the failure of this.

2 = Fault located somewhere in the supply system, either in the injectors, in the fuel pump, etc.

3 = Failure due to a defect in the ignition system of the vehicle. It can be in the coils, detonation sensors, etc.

4 = Failure in some anti-pollution system as a catalyst, heated oxygen, secondary air, etc.

5 = Failure in the system of minimum gear and speed.

6 = Fault in the Engine Control Module (ECM) and auxiliary outputs. It can refer to a fault in the memory or the processor, as well as its processing circuits or other parts.

7 and 8 = Fail somewhere in the automatic transmission or 4-wheel drive control system.

Then, as a summary, the code is composed of:

  • A letter (P, U, C or B), which indicates which system the fault comes from.
  • A second value (number) that indicates what type of code it is (universal or made by the manufacturer).
  • A third value (number) indicating where the problem specifically originates.

What is OBD protocol?

The OBD protocol is an on-board diagnostic system used in cars and trucks.

The first OBD regulation that came on the market was the OBDI, this was only responsible for monitoring some components in the emissions of the vehicle. Nowadays, this regulation is not very common, it is much more used the OBDII protocol that we will talk about next.

What is the OBDII protocol?

The OBD2 protocol, on the other hand, is the most up-to-date regulation of the OBD diagnostic system. OBDII goes beyond just monitoring some emission components; it detects chemical, electrical and mechanical faults that can negatively influence vehicle emissions. Therefore, this system is much more complex than its predecessor, going so far as to provide greater safety and ecology.

Immediately after the system has detected a fault, it alerts the driver via the Malfunction Indication Lamp (MIL), also known as Service Engine Soon or Check Engine on various car models.

This protocol uses DTC codes to indicate system faults.

What is the EOBD protocol?

The EOBD protocol is almost the same as the OBDII, only that it is used for European cars (the E at the beginning indicates that it is a European protocol). Unlike OBD II, it does not control the emissions from the fuel tank. However, this protocol is more complex than OBD II, since it makes use of a kind of "maps" in relation to the current conditions of the engine. In addition, the components are automatically calibrated and easily adapted to the system. Therefore, the user must use high quality spare parts, specifically designed for the model he is using.

There is another type of OBD2 protocol, the JOBD for automobiles in Japan.

 How can you solve a DTC code?

Solving an automotive DTC code will depend a lot on the type of problem that is diagnosed. Usually, replacing a sensor is enough, since most faults are due to electronic problems, especially in the sensors.

Of course, in the event that any other fault is diagnosed in the mechanical system, the obvious solution is the replacement or repair of the damaged part.

Since it takes knowledge of the meaning of each code to be able to repair it, here at fixtroublecodes.com, you can find everything you need to know about DTC codes; their meaning, what causes them, what symptoms they present, and, above all, the possible solutions to the problem.


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