Prepare a blank USB memory stick with only 2 files inside: Lv2Diag.self (file 1) and the modified 3.41 PUP file.
These must be in the root of the memory stick. No other file must be present.
- Insert the Device Flashed with the downgrade firmware in your console.
- Turn on the PS3 using the standard sequence; Remove power (or power plug) from the PS3,insert Device into USB port, power on, then quickly press eject.
After a very short while the PS3 will power off.
- Turn on the PS3 to confirm that it is in Service Mode. You should see a red box on the screen saying Factory Service Mode it will be low res.
. Turn off the PS3 and remove Device
- Insert the USB memory stick with the 2 files on in the "right USB port" of the PS3 and turn it on.
The screen will be black, but the LED on the PS3 will blink.
- Wait for approximately 3 minutes. In the end the PS3 power button will flash green and then the PS3 will turn off.
Wait 3 minutes for the system to install the old FW, towards the end the power button on the console will start flashing green and then your console will power off.
- Remove the USB memory stick and turn on the PS3. It will still be in service mode. you can now verify that it has been downgraded to v3.41. If you wish
to downgrade to an earlier firmware you can do so now, there is no need to use modified custom PUP when the firmware has already been downgraded to 3.41.
- Insert USB drive in PC, delete the 2 files, and copy LV2Diag.self (file 2) to it.
- Insert USB memory stick and power on the PS3. After approximately 10 seconds it will power off.
- Remove the USB memory stick and power on the PS3. The procedure is now complete.

What device are you using to downgrade?

Those two files for the usb are what you use once in facorty/service mode to actually downgrade the ps3.