All work is by other people who posted the original info. I take no credit for their work. It would take another complete post to thank those responsible for providing the information below.
I cannot be held responsible if you try any of these procedures, and your phone becomes inoperable or otherwise damaged. Read thoroughly before performing these actions to your phone. Know the risks, and understand what you are doing before trying anything.
I put this post together because I noticed that folks on our forum ask these questions multiple times on a daily basis. I don’t know how some of our more experienced users bounce around all day to answer them. I also noticed there is no one place to find all the info below. I had to dig through many threads for hours to get this together. This is a work in progress and will change as new info and better methods arrive. If you find a better way to do this or outdated information, please let me know and I will update. Thanks
RUU – Rom Update Utility. It is a Windows based exe file that contains a complete operating system including a stock recovery, bootloader (Hboot), and radio (Baseband.) This program is run to bring the phone back to a stock state while the phone is in bootloader mode.
OTA – Over the air update. It is an update package used to update a stock operating system. It is not a complete operating system and contains only parts that are getting an update . You can’t install an OTA on a modified device, only stock.
Bootloader (Hboot) – The Bootloader or Hboot, is like BIOS to windows. It is the first thing that runs when you boot up your Android device. It packages the instructions to boot the operating system kernel and most are specifically designed to run their own debugging or modification environment. Basically, an Android device is like a hard drive that has several partitions, which holds the Android system file in one and all the app data in another. For all these partitions, Bootloader (or Hboot) serves as a security checkpoint that is responsible for checking and initializing the hardware and starting software. There's a common misconception that can you just change the hboot but that isn't the case, you need the full firmware that comes with the RUU.
Bootloader mode / Fastboot mode – One and the same. This is the environment where you can flash a custom recovery (the stock recovery has very little options), flash Roms, etc. To enter Bootloader mode, power down the phone and then hold the power key and the volume down key at the same time until the phone enters bootloader mode. If your computer is not connected you will see “Fastboot” highlighted in red. If your computer is connected you will see “Fastboot USB” highlighted in red. This still does not mean that your computer can communicate with the phone. More on that later.
Firmware – The image version i.e. 3.18.502.6, 2.20.502.7 etc. The firmware contains the Hboot so don’t confuse the Firmware version number with the Hboot version number or Baseband version number. You can check this out in more detail while looking at the RUUs available and it will make more sense. Each software version is connected with the CID (Carrier ID) and MID (Model ID) of your device. That means you can't use whichever version you want, unless you have S-OFF on your device. Each ROM Update Utility.exe package will check your device details (bootloader version, MID and CID) before starting the update process.
Baseband (Radio) - The baseband (radio) is completely separate from the ROM, it's stored in an entirely different partition. Don’t confuse this with Hboot or Firmware.
Note: This guide may or may not apply for the UTL middle eastern variant. I think the jury is still out on that. If anyone has additional info it would be a big help for many of our users.
S-On – If you are S-On then you must pay particular attention to the RUU you choose to install. If you have obtained SuperCID then you need to gain S-Off in order to run a RUU. You WILL brick your phone. Remember this, S-On + SuperCID + 3.18 RUU = Brick. Make sure your CID is not 11111111, 22222222, or any other variant of SuperCID. If so, it’s time to S-Off. I recommend the following links:
But if you wish to remain S-On and currently have a stock CID (verified) then you can run the appropriate RUU while in bootloader mode. If your bootloader is unlocked then you must relock it prior to RUU. You must use an RUU that matches your CID and carrier. You can use the same version that is installed on your phone or a higher version (again that matches your CID and carrier.) This is normally done to fix issues, upgrade a stock phone manually, or start over with a fresh install.
S-Off – If you are S-Off you may choose several versions of RUU. It is recommended that you choose 3.18 which comes with the 2.14 Hboot. If you want to run a Sense based Rom you may experience data and wifi issues and are further recommended to upgrade your Hboot to 2.15:
If you plan to use an AOSP Rom (4.3 and higher) then the 3.18 RUU is a requirement. You do not need to upgrade your Hboot to 2.15 to use an AOSP Rom.
1. Download the RUU file you need. It will be an exe file (remember what I said above about S-On and S-Off.)
2. Backup all your files you wish to keep and make a backup of the phone in recovery (if you have a custom recovery.) When I run the RUU on my phone, it doesn't erase the files on my internal storage (SD Card partition) but I still back it up just in case. I recommend you make a back up too.
3. Install the most current HTC drivers.
It is recommended that you install HTC sync to get the drivers and then uninstall HTC sync but keep the drivers if you are having connection issues. If you have windows 8+ then you may encounter connection issues known to exist with the new windows. If possible, use a Windows 7 computer.
4. Install Fastboot and ADB drivers. I’m including some links to help you understand what this is and how to use them if you don’t know.
5. Make sure you charge the phone. I recommend 100% (leave no room for doubt.)
6. Place the phone in bootloader mode by powering down and the holding the power key and volume down key at the same time until the phone boots into bootloader.
7. Connect the phone to the computer.
8. If you are matching your current Firmware you need to type the following in a CMD prompt: “Fastboot getvar all” and check your firmware. If you are S-On and you have 3.18 you can’t downgrade. You must stay at 3.18. If you are on a lower version than 3.18 then you can go higher.
9. Make sure no other programs are running, make sure screen saver/hibernation is turned off.
10. Run the RUU exe file and follow the prompts. Be patient, There will be times when it appears to be doing nothing but it is still working.
11. After it finishes, (it usually takes 15 to 20 minutes) if you are stock, reboot into system. If you are modified, you will need to reflash a custom recovery, custom Kernel, Radio, etc.
I’m hoping this guide helps those who don't understand the RUU process. I know I learned a lot putting this guide together. Using a RUU was a concept I had to read a lot about and search around quite a bit to understand. I personally ran these instructions several times with the 3.18 RUU and everything went fine.
Special thanks goes to Timmaa. He must type the acronym RUU about 100 times a day helping people and many tidbits of info in this guide were taken from the advice he gives. I'm hoping I can save his keyboard/touch screen from wearing out!