Here is how you interpret the LEDs to get the code number:

Four lights flashing      = 0
One light flashing     = 1
Two Lights flashing      = 2
Three lights flashing     = 3

1. Turn the xbox 360 on, and wait till the 3 red lights are flashing.
2. Press and HOLD the Sync up button(the small white one) continuosly throughout the entire code.
3. Toggle the eject button on the ODD. The LEDs will now blink the first number in the code.
4. Toggle the eject button on the ODD again. The LEDs will now blink the second number of the code.
5. Toggle the eject button on the ODD again. The LEDs will now blink the third number of the code.
6. Toggle the eject button on the ODD again. The LEDs will now blink the forth number of the code.
7. Toggle the eject button on the ODD again. The LEDs will go back to the 3 red flashing lights.
8. Write your code down!!! It’s easy to forget the sequence.

Here’s the codes in groups:
The 00’s

0000 = Sync Button not press firmly or bad.
0001 = Power supply problem. Swap for a known good PS.
0002 = Network Interface problem
0003 = Power problem checkthe PSU could be the GPU/CPU, No clean power from the power supply.

0010 = over heating
0011 = over heating – Check to see if all 8 of the heatsink screws are tight.
0012 = over heating
0013 = over heating

0020 = Possibly overheating.
0021 = DVD Drive Time out – Problem with a firmware flash or Problem with the SB chipset on the motherboard.
0022 = GPU Error – GPU Overheating or Missing SMD on bottom of mainboard. Also missing GPU entirely (TMF)
0023 = (not yet known)

0030 = (not yet known)
0031 = (not yet known)
0032 = (not yet known)
0033 = (not yet known)

The 01’s

0100 = (not yet known)
0101 = (not yet known)
0102 = Something wrong with the GPU / VRAM or a missing SMD under the board.                                     0103 = CPU Error/ CPU Overheating – see solution for error 0102

0110 = Memory Error / Memory Overheating – see solution for error 0102
0111 = (not yet known)
0112 = (not yet known)
0113 = (not yet known)

0120 = (not yet known)
0121 = (not yet known)
0122 = (not yet known)
0123 = (not yet known)

0130 = (not yet known)
0131 = (not yet known)
0132 = (not yet known)
0133 = (not yet known)

The 02’s

0200 = (not yet known)
0201 = (not yet known)
0202 = (not yet known)
0203 = (not yet known)

0210 = (not yet known)
0211 = (not yet known)
0212 = (not yet known)
0213 = (not yet known)

0220 = (not yet known)
0221 = (not yet known)
0222 = (not yet known)
0223 = (not yet known)

0230 = (not yet known)
0231 = (not yet known)
0232 = (not yet known)
0233 = (not yet known)

The 03’s

0300 = (not yet known)
0301 = (not yet known)
0302 = (not yet known)
0303 = (not yet known)

0310 = (not yet known)
0311 = (not yet known)
0312 = (not yet known)
0313 = (not yet known)

0320 = (not yet known)
0321 = (not yet known)
0322 = (not yet known)
0323 = (not yet known)

0330 = (not yet known)
0331 = (not yet known)
0332 = (not yet known)
0333 = (not yet known)

The 10’s

1000 = (not yet known)
1001 = (not yet known)
1002 = (not yet known)
1003 = Hard Drive Error or Bad Hard Drive itself or internal connection to the hard drive, Try removing it.

1010 = Hard Drive Error, Can be caused buy a corrupt or missing eProm.
1011 = (not yet known)
1012 = (not yet known)
1013 = (not yet known) possibly a dashboard update error

1020 = (not yet known)
1021 = (not yet known)
1022 = AV cable error… Try a different AV cable. Also check switch setting. (Could be encoder chip)
1023 = DVD drive not connected, connect DVD drive to boot

1030 = (not yet known)
1031 = (not yet known)
1032 = (not yet known)
1033 = (not yet known)

The 11’s

1100 = (not yet known)
1101 = (not yet known)
1102 = (not yet known)
1103 = (not yet known)

1110 = (not yet known)
1111 = (not yet known)
1112 = (not yet known)
1113 = (not yet known)

1120 = (not yet known)
1121 = (not yet known)
1122 = (not yet known)
1123 = (not yet known)

1130 = (not yet known)
1131 = (not yet known)
1132 = (not yet known)
1133 = (not yet known)

The 12’s

1200 = (not yet known)
1201 = (not yet known)
1202 = (not yet known)
1203 = (not yet known)

1210 = (not yet known)
1211 = (not yet known)
1212 = (not yet known)
1213 = (not yet known)

1220 = (not yet known)
1221 = (not yet known)
1222 = (not yet known)
1223 = (not yet known)

1230 = (not yet known)
1231 = (not yet known)
1232 = (not yet known)
1233 = (not yet known)

The 13’s

1300 = (not yet known)
1301 = (not yet known)
1302 = (not yet known)
1303 = (not yet known)

1310 = (not yet known)
1311 = (not yet known)
1312 = (not yet known)
1313 = (not yet known)

1320 = (not yet known)
1321 = (not yet known)
1322 = (not yet known)
1323 = (not yet known)

1330 = (not yet known)
1331 = (not yet known)
1332 = (not yet known)
1333 = (not yet known)

1444 and up There is no “4″ in the error codes four lights is a “0″ go back and check your code again.

2000 to 3333 haven’t seen any yet.

There’s a lot missing and they need to be figured out. If you know any of the (not yet known) please post.

I will update later to correct any I find.

There’s also some work being done on the SMC that may yield all these codes exactly. Hopefully.

Credits go to llamma.com and all the hackers here at XBH fourms.