All modern vehicles has a computerized engine control systems. Those systems have a certain amount of built-in self diagnostic capabilitys to detect problems that can affect engines performance and emissions or fuel saving. The same is for the antilock brake system, stability control system and other onboard systems that are connected to vehicle computer and controlled by this computer.

As a fault is detected, vehicle computer will store a diagnostic trouble code in its fault memory and illuminate the “Check Engine” light (hhen the check engine light is on, the car is likely to be wasting fuel, polluting excessively, causing premature part failure, or perhaps all three) or other light if there is different lights on the dashboard for different vehicle systems and modules. On some older vehicles, computer can be put into a special diagnostic mode by grounding certain contacts on a diagnostic connector in this vehicle. This will cause the Check Engine light or other lights to flash out the fault code. On allmost all modern vehicles, though, a scan tool must be plugged into the vehicles diagnostic socket to connect to computer system so you can access, read and delete these trouble codes.

DTC codes (Diagnostic Trouble Code) can tell you what could cause a problem in the vehicle. As you put the vehicles computer to the spacial diagnostic mode it flashes Check Engine (or other) lights in the dashboard so you can count numbers of DTC code. All DTC codes are made from four numbers. These numbers indicates what kind of Diagnostic Trouble Code you should check in any awailable DTC database on the web. The best way to check these faults is to read fault memmory out from the vehicles diagnostic computer through special diagnostic tools. Some of these tools just gives you a DTC code and some of them can show you short descriptions of these faults.