How does OBD read diagnostic trouble codes

Before learning to read diagnostic trouble codes,you should know much about types of codes read.
Actually,there are two different types of codes read:diagnostic trouble codes and pending codes.The first codes are used to help determine the cause of a problem or problems with a vehicle.
The second codes are also referred to as “continuous monitor” and “maturing codes”. An intermittent fault will cause the computer to store a pending code in memory. If the fault does not recur within 40 warm-up cycles, the code will be cleared from memory.
If you have a well recognise about  trouble codes then you should obey the following steps to make your OBD work：

• press and release read key: Refer to the general scan tool manufacturer’s operation manual to access powertrain DTC
• observe a Moving * on Display:If a “fall” message displays,cycle ignition key to the OFF position for 10 seconds, then back ON and repeat ” reading diagnostic trouble codes”.

• view codes on display:If there're no diagnostic trouble codes present, the tool will display “No codes”.

If you do as above step,then you have successfully control how to use OBD read diagnostic troble codes. And here we also recommend some hot car tools such as MB STAR C4 and x431 gds.

X-431 GDS Smart Package

As standard all X431 GDS Smart Packages have full Professional Diagnostic Tools functions, internet access for Auto database, immediate email feedback and simple online one click upgrades via either Wi-Fi or LAN.
As with many other products available from Launch, the X-431 GDS covers vehicles from Alfa Romeo through to VW – an estimated 98% vehicle parc coverage.
Included in all standard X-431 GDS Smart Packages you get all the great features and benefits listed in this leaflet:

* Main unit
*Smart OBD II – 16 diagnostics
connector and cable
*Power adapter
*Printer paper
*Touch screen stylus
*User manual
*SW & HW packaging list

As with most items you can tailor your
X-431 GDS further with some
recommended optional extra’s including:

*Non 16 pin connector kit 
(as with current X-431
Diagun)
*Workshop stand
*Autodata vehicle
information system
*Cable set auto test aid

X-431 GDS Features:

*Fast Diagnostic speed
*One key upgrade
*Robust industrial application design
*Access to database by WiFi
*Full colour screen
*User friendly application interface
*Compliant with projector
*Extendable to more function modules
*Software 1 year free upgrade

Specification:
*Windows embedded standard OS
*7“ TFT high definition colour touch screen
*32bits CPU
*Hard disk capacity:8G
*Wi-Fi and LAN
*2 USB ports
*Main unit power supply:DC14V
*Suitable for 12V and 24V vehicles
*Working temperature:-10°C ~ 55°C