0020 Xbox 360 secondary error code | Three red rings guide
A complicated problem
This issue is very complicated and should be assessed by pros only. If you have the 0020 secondary error code on an RROD Xbox 360 console, your best bet is replacing the motherboard. Most people will not be able to check the problems causing it. However, I will go into the issue further below.
Signal check
Officially, this secondary error code is caused by the GPU reset communication. If this test is not completed successfully on boot up, you will get this 0020 error code on the Xbox 360 console. This can be caused by TONS of components as there are multiple areas that manage this info, and could be bad. You can start by checking the signal itself being at the 3.3v range with a multimeter.
USER EDIT/ADDITION: User "GeneralFranklinstein" submitted additional info for this point. I did get verification on this from other sources but must be honest, this is beyond my knowledge and was not verified by me, so take this with a grain of salt. The 3.3V check should be done at the FT2P13 line on the Xbox 360 phat console, the FT3R16 line for a trinity (Slim) motherboard, or the FT3T2 for the Corona (Slim) motherboard.
As stated, the signal is done as soon as the console starts to boot up, so you must be ready to get your read out the second you turn on the console. If this is bad or off voltage, there are two main resistors you should check next. I currently don't have the exact mobo pin locations but they should be attached to that same line as above. There is a 1K ohm and 10K ohm resistor to check. If signal and resistors are good. The issue will be the southbridge and would need to be replaced or reflowed.
The GPU
There are other signals you could check but in general, at this point your GPU would more than likely be to blame and should be reflowed or replaced. The 0020 secondary error code is also caused or blocked by multiple resistors not mentioned but are much more rare in my opinion. If you are at this point your best bet is the GPU or replacing the motherboard. The Xbox 360 console has many errors but by far this one is one of the most complicated. This is why every single detail will not be gone through here.
