Diagnostic trouble codes, in broad terms, are codes that computer diagnostic system in a given car has. The system displays a certain code depending on what kind of problem that the system can detect from inside of a car.
Diagnostic trouble costs are used to help car mechanics and owners with a rich expertise in car maintenance understand problems with the car and where the root of the car’s problem or problems may lie.
These codes must be used along with the car’s manual to determine what needs to be examined and tested to properly diagnose a car’s problem whether from professional OBD 2 software or with a car code reader.
The the best understanding of possible causes of problems with the car, refer to the car’s manual. A car’s parts or components should not be replaced without reference from its manual, even if you have a clear identification of the DTC and what it describes.
For instance, if a DTC notifies you of a sensor problem, the solution of that problem might not be to replace the sensor, but rather to replace another component that the sensor is affiliated with. You may even likely just need to fix or replace the wiring of the sensor alone in order for the problem to be solved.
DTCs can also be activated by faults in the foreseeable future, giving you inaccurate codes for problems or notifying you of a problem that may not even exist with the car in the first place.
For instance, a muddled MAF sensor could lead the car’s system to believe that the car has fuel mixture problems, when in reality, the sensor is causing the car to mix fuel unevenly.
In order to prevent unpredictable and unexpected DTC codes, as well as ensure that you understand fully what could be wrong with your car as problems occur, purchase a good OBD 2 scanner that is programmed to help car owners and technicians better understand a car’s specific problem or problems.
DTCs come in a string of five characters. One code for example, might be “P0806”.
The first character will either be P (powertrain), B (body), C (chassis) or N (network). This character will help you determine which of the four main car’s parts is at fault.
The second character either will be a 0 or 1. 0 means it is a generic OBD 2 code. 1 means it is a car manufacturer exclusive code.
The third character can be one of many letters or numbers. This list of characters include 1 (fuel and air metering), 2 (fuel and air injector circuit), 3 (ignition), 4 (auxiliary emission control), 5 (vehicle speed and idle control systems), 7, 8 or 9 (transmission) and A, B or C (hybrid propulsion).
The fourth and fifth characters in the code represent a specific description of the problem with the part and system in question. These are numbered by “00”, “01”, “02” and so on.
In total, there are over 5000 generic and manufacturer exclusive OBD 2 troubleshooting codes that exist. You can refer to our master list of DTCs to help you best understand your specific car problem based on your code.
As explained earlier, general DTCs start with P0XXX, and manufacturer exclusive DTCs start with P1XXX. Generic DTCs are defined in the standards for OBD 2 and EOBD 2, and applies to all official car manufacturers.
Manufacturer exclusive DTCs, however, are not available in the generic code databases, and are instead created and defined by a car manufacturer for all the cars they make.
The definition for the code is defined in the EOBD / OBD-II standard and will be the same for all manufacturers.
Where manufacturers feel that a code is not available within the generic list, they can add their own codes. The definitions for these are set by the manufacturer.
P0xxx - Generic
P1xxx - Manufacturer-specific
P0xxx - Generic
P30xx-P33xx - Manufacturer -specific
P34xx-P39xx - Generic
C0xxx - Generic
C1xxx - Manufacturer-specific
C2xxx - Manufacturer-specific
C3xxx - Generic
B0xxx - Generic
B1xxx - Manufacturer-specific
B2xxx - Manufacturer-specific
B3xxx - Generic
Network Communication codes
U0xxx - Generic
U1xxx - Manufacturer-specific
U2xxx - Manufacturer-specific
U3xxx - Generic
CTL + F
COMMAND + F
OBD 2 systems survey all the functions pertaining to emissions from inside the car. This includes fuel, emissions, catalytic converters, evaporative emissions and more. So long as the vehicle in in operation, all of these functions can be monitored. The OBD 2 system can undergo self-tests by itself periodically.
The OBD 2 system can relay one or more DTCs according to any and all problems that it senses throughout the car. Once the problem is detected from inside the car, the OBD 2 system will respond accordingly by sending out this code for an OBD 2 reader can receive. For you to know when there is a problem that you cannot notice right away, the “Check Engine Light” on your dashboard will turn on.
Your “Check Engine Light” should automatically turn on when your car starts to run, and will stay on for as long as the car is in operation until the specific problem that the OBD 2 system detects is fixed.
In some instances, the light may actually blink or flash on and off when a problem is apparent to the system. There are even times in which the “Check Engine Light” is on at certain times and is not on at other times; indicating that the system only notices the problem some of the time.
When you or a professional mechanic fix the problem in question with your car, only then will the “Check Engine Light” go out, and in most cases, there is nothing additional that needs to be done for this light to remain off as your car turns and stays on.
It is important to know that your car will not clear an OBD 2 emissions test if your check engine light is on and there is a DTC that your car’s system is relaying. The “Check Engine Light” should be off and no DTC code present in the system in order for your car to pass this test. Additionally, any and all OBD 2 self-monitors should come back without finding any problems with your car.
The only purpose of the “Check Engine Light” is to alert the car owner of an emissions-related fault in the car. This light does not notify you about the specific problem that activates the DTC, bor does it signify the severity of the problem, or what the solution to the problem is. Contrary to common belief, “Check Engine Light” is not a solution to any problems that you might have with your car or its systems.
It is also important to realize that the “Check Engine Light” is not a warning light that is used for general purpose, such as your car’s turn signal arrows, with lights that also appear on your dashboard.
Severe problems such as loss of oil or overheating engine will turn on other warning lights on the dashboard, but not the “Check Engine Light”.
There is no clear-cut explanation as to why your “Check Engine Light” turns on. The only way to realize why the light is on is to connect your car’s OBD 2 diagnostic connector with professional OBD 2 software or with a car code reader.
Either one of these tools will display one or more DTC codes that the car’s system will identify.
Depending on the tool or software you use, you should get a five-character code followed by a description or definition of the code. More basic readers might only give you the code itself, leaving you to look up the code in a list or database.
You won’t be able to diagnose your car’s problem without one of these scan tools. If you do not own a scan tool, you can take your car to an auto parts or hardware store. Many of these offer free plug-in diagnoses to determine what code your car’s system gives. Repair shops and dealerships also offer plug-in diagnoses, but they usually cost money and are included in any repair jobs that you may agree to pay to have from them.
If you have the trouble code that relates to your car’s problem, write it down. Do not erase the code from the software or tool that you are using, as you will need this code to find the solution to your car’s issue.
As mentioned previously, a competent OBD 2 scanner tool should include a description of the problem next to the code. If your scanner doesn’t include a description, you will need to find one either online in a database or in your car’s manual.
An OBD 2 scanner is the best and safest way to erase a DTC from your car’s system. This scanner communicates with the car’s computer and instructs the computer to erase the code. It does not change or tweak the settings from inside the car or its systems.
Do not disconnect the battery, as it is the worst way to erase a DTC from your cars’ system. In older cars, especially made before 1996, unplugging the battery or taking out the power fuse will remove all the settings that the car’s computer has saved, along with the DTC(s).
It is important to note that clearing the DTC will not turn or keep the “Check Engine Light” off. Some time afterwards, the car’s system will again identify the problem with your car and the light will turn back on again. Only solving the problem will get the light to stay off.
We do not advise disconnecting the battery on vehicles made after 2005 in order to clear a DTC, as it can make the PCM to forget crucial settings with your car’s computer or network. If this happens, you might need the car to “relearn” your settings via special procedures, which would involve a scanning tool that would restore the affected system in the car and get it back to normal.
If you erase your DTC with an OBD 2 diagnostics tool or disconnect the battery and reset your OBD monitor systems, your vehicle will not be qualified for an OBD plug-in emissions test until each monitors has ran and is cleared.
The process of setting up an OBD 2 scanner for your car ultimately depends on the make and model of the car itself. When you buy a new scanner, there is a one-time setup procedure you must do so that your scanner can be custom-tuned to your car in particular.
Firstly, download any required software on your smartphone or computer. If you are communicating with the scanner though a computer, you may also need to connect via wireless Bluetooth.
To connect the scanner to the car, there is a 16-pin connection point that you must plug the scanner into. This connection point is often located on the driver’s side underneath the dashboard. Each pin on this connection point has their own source of power, as OBD pins are designed to suit various areas throughout the car.
With the software installed and the scanner connected, try to navigate through a menu either with the tool, your computer or our smartphone. On a standalone tool, there are buttons to press to navigate through menus, such as arrow keys and other buttons.
The objective of the OBD 2 scanner is to scan the car for any problems, of course. So long as the scanner is compatible with your car, it should be able to work with all of the components throughout it.