Xbox 360 Error Codes
The Xbox 360 error codes can be divided into two categories. The primary category is related to the Flashing LEDs and the numeric codes as displayed on the screen. There are Secondary or "Hidden" codes that can be accessed and utilized if the screen is not working. These codes are also accessed via the Flashing LEDS.
Primary Flashing LEDS
There are 4 primary error codes associated with the Flashing LEDS. They are:
1 Red Light which signifies a hardware failure. The specific hardware failure can range from a problem with the DVD, Hard Drive, AV Cable or Ethernet. There are also errors for which there is no known cause. The specific hardware failure code will be displayed on the screen.
2 Red Lights which signifies overheating. Overheating can be caused by blocking of the console vents or problems with the fans etc. One way to rectify this problem is with after market cooling fans. You can also try replacing the thermal paste for the heat sinks. As mentioned in the section on RROD Causes heat is the problem.
3 Red Lights is what we all dread and means the console has suffered a General Hardware failure (CPU/GPU/processor problem). This error code will probably require checking the Secondary Error codes. The most popular fix for this error code is the X-Clamp Repair. You can watch the videos on this website to see how it is done. You can also purchase a kit on this website to eliminate this problem.
4 Red Lights means your AV cable can not be detected. This error is often mistaken for RROD. Do not panic. Check to make sure the AV cable is connected to the Xbox 360 console. You can also try cleaning the metal area that plugs into console. Worst case scenario try a different AV cable.
Secondary "Hidden" Error Codes
If your screen is not visible you can find out what kind of hardware failure has occured by prompting your console to flash the error code to you. The sequence and rate of flashing will reveal the codes.
How to find the "hidden" Error Codes
Turn your Xbox on. Press the sync up button and keep pressing it, at the same time press the eject button. Your LEDs will now flash the first number in the code. When you release the eject button and press it again it will give you the second number. You basically repeat that 4 times total.
The way you interpret the lights is simple. If all four lights are flashing the number equals zero. If one light is flashing the number equals one. Two lights flashing equals two and three lights flashing equals three.
Error Code Map
There are other sites that give the codes and their meaning. One of the best sites I have found lays this whole process out very systematically and concisely. Follow this link Xbox 360 Error Code Map