[OBD2 scanner basics] How to understand trouble codes and clear them

If your check engine light keeps coming on but you don’t know how to understand trouble codes, then this article is for you!

You’ve been driving around town and suddenly, your car engine light comes on. You can’t figure out what’s going on or what the lights mean because the car is running fine. The car isn’t stalling and there’s no noise coming from under your car’s hood. Then what seems to be the problem? It’s a trouble code.

The “Check engine light” which came up means your car has an OBD II Trouble code (could be more). Whenever this OBD II (Onboard Diagnostic System) identifies a problem, your vehicle’s car engine light (also known as Malfunction Indicator Lamp – MIL) will show up to warn you. And this detected problem is capable of causing your car’s emission to rise higher by 1.5 times the official limit.


When the check engine light is on, here’s the skill of reading the trouble codes needed

What is a trouble code?

A trouble code is a code a car’s OBD system makes use of to alert or warn a car driver that there’s a problem. When it identifies a fault, it activates the trouble code which corresponds to the fault. So, each fault has a trouble code that corresponds to it.

The trouble code list was originally written by the Society of Automotive Engineers (SAE), to be used by all automotive manufacturers to agree with the OBD II emission regulation in the USA. European and Asian car manufacturers have also adopted the same trouble code list.


How to understand trouble codes? Keep reading!

Types of trouble codes

The trouble code list has been categorized into four systems namely:

  • Body (B) codes cover lighting, climate control, airbag, etc.
  • Powertrain (P) codes cover transmission, engine and emission systems.
  • Chassis (C) covers mechanical systems like antilock brake, steering and electronic suspension systems.
  • Network communications (U) covers the modules and controller area network wiring bus.
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Furthermore, these codes are divided into 2 major groups:
The Generic or Global codes and the Enhanced or Manufacturer codes and this followed information will help you learn how to understand trouble codes.


Trouble codes can be cleared with the help of a scan tool

Generic or Global codes

The codes that has “0” as their second digit are the generic codes. These codes have been adopted by every vehicle that complies with the OBD II regulation. It means the code is common to every car and model, and it is used to diagnose basic emission faults.

Enhanced or Manufacturer specific 

Here, codes that has “1” as their second digit are enhanced or manufacturer specific. These codes are not common with every car or manufacturer’s model. The codes are unique and are used by specific cars or model to identify additional diagnostic faults that go beyond the generic codes.
The OBD II system detects all problems aside frome emission-related faults. They include engine misfires, fuel and ignition system, catalytic conversion and many other emission systems (PCV, EGR, etc.)

A lot of these functions are checked whenever the car is being driven. And for others, a certain driving condition must be met before the functions can be monitored. Some self-tests like looking out for fuel vapor leak, are run repeatedly by the OBD II system. If a system notices a signal that seems to be outside normal limits or a system that fails a self-test, it will be stored as a diagnostic trouble code (DTC), and the “Check engine light” will be turned on by the OBD II system to alert you that there’s a problem.


Always think of the scan tool when the check engine light is on

Most cases have confirmed the check engine light comes on and stays on until the fault has been fixed or the code clears. For an engine misfire case, the light may keep flashing on and off as the fault is happening. Another case also confirmed the light going off and on for some time when the fault has already been fixed.

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How to understand trouble codes

There are common reasons why engine light is on. But if you have checked them all and everything is fine, the only one way to find the faulty parts is through a scanning tool. Simply have a scan tool plugged into your car’s OBD II diagnostic connector. It will show the trouble codes as they have been set. Almost every scan tool displays the trouble code, with a one-line definition of the code. Some simple code readers might give only the number, with no definition

Also note: If there’s no scan tool, you won’t be able to diagnose a check engine light. What some vehicles will only do is to enable you to access the trouble codes through the driver information display (You should know the procedure to be able to do it).

Do you have a scan tool (might be expensive for you)? If you don’t have one, a lot of auto parts store and repair shops in Nigeria can conduct a FREE computer diagnosis that will read out the codes. However, auto diagnostic service centers collect a fee to diagnose the fault responsible for the “check engine light” that’s on.


Don’t remove the battery to clear the codes, that might result to adverse outcomes

Do you have a trouble code? Write the code numbers down on a paper because you will need the code to identify the problem.
The code number will reveal to you the system or sensor that has a fault. If a description of the fault is not given by the scan tool, you can check for it online or any diagnostic shop.

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How to clear trouble codes

The safest and best way to clear the trouble code is through the use of a scan tool. The scan tool connects with the vehicle computer and transmits information to it that the trouble codes should be cleared.

You can clear trouble codes by disconnecting the battery but this way is not recommended. For older vehicles made before 1996, when you disconnect the battery for only a few seconds or remove the power fuse, all the codes will be removed, including other learned settings that have been stored over time by the computer. You can read more aboutthe 5 possible consequences of disconnect or replace the car battery in our previous article.

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Note this: When you clear the codes, it doesn’t mean the check engine light will go off. In case you have fix the problem and the engine light is still on, you need to know how to reset the check engine light. But if the problem that triggered the check engine light to come on in the first place has not been fixed, it will turn on again and the trouble codes will still reset.