The official Android 6.0.1 Marshmallow firmware for the ASUS ZenFone Selfie (Z00UD / ZD551KL) is version V21.40.0.1999. Firmware Details Model Name: ASUS ZenFone Selfie (ZD551KL) Model Number: Z00UD Android Version: 6.0.1 (Marshmallow) Build Number: WW_21.40.0.1999 Region: Worldwide (WW) Official Download Link
You can find the firmware file directly on the ASUS Support Website. Installation Instructions
Check Version: Ensure your device is currently running the latest Android Lollipop version before jumping to Marshmallow. Download: Download the .zip file (do not unzip it).
Transfer: Connect your phone to your PC and move the file to the internal storage root directory (not inside any folder).
Update Notification: Disconnect the cable. A "System Update File Detected" notification should appear in your status bar.
Install: Tap the notification and follow the prompts. Ensure your battery is above 15% and you have backed up your data.
Note: Upgrading to Android 6.0 will remove APP2SD support. Move any apps stored on your SD card back to internal storage before updating.
The notification arrived on a Tuesday, thin as a whisper: “System Update: Android 6.0.1 (Marshmallow) – 1.21 GB.” asus zenfone selfie z00ud firmware 6.0 1
Lena stared at her ASUS ZenFone Selfie’s screen. The phone, a lavender-gray brick with a charmingly ridiculous 13-megapixel front camera, had been her loyal companion for two years. It had survived a drop into a bowl of ramen broth and a winter stuck on Android 5.0 Lollipop. Lollipop was reliable—clunky, battery-hungry, but reliable.
But this update, labeled WW_6.0.1_23.40.0.3_20170112, promised change. “Do you want to install?” it asked.
She tapped “Yes.”
The phone rebooted. The ASUS logo glowed. Then, the little green android appeared, belly-up, with a spinning blue wireframe globe on its chest. The progress bar crawled. 10%. 30%. 50%. Lena made tea. 80%. She checked Instagram on her laptop. 99%.
Then, silence.
The screen went black. Not the “off” black—the void black. A tiny red LED blinked near the earpiece, like a dying heartbeat.
“No. No, no, no,” she whispered.
She pressed the power button. Nothing. Power + Volume Up. Nothing. She plugged it in. The LED glowed solid red for a moment, then returned to its slow, desperate blink. Her Selfie was a brick. A pretty lavender-gray paperweight.
Three hours of frantic Googling later, she found them: the ghosts of XDA Developers.
A thread titled "[GUIDE] Unbrick Z00UD – Raw Firmware Flash (6.0.1)" was her only hope. The instructions were a ritual of desperation:
At 2:00 AM, her laptop screen flickered. Device Manager refreshed. A new device appeared: "Cloverview Plus" with a yellow exclamation mark.
She had entered the DNX mode—the phone's deepest emergency bootloader. A place most users never see.
The command line was her language now. She typed:
> fastboot flash boot boot.img
> fastboot flash system system.img
> fastboot flash recovery recovery.img The official Android 6
Each command felt like defusing a bomb. The phone's tiny red LED would flash faster with every successful write. Finally, the last line:
> fastboot reboot
The screen glowed. The ASUS logo returned, but it was sharper, cleaner. Then, the new setup wizard appeared—Android 6.0.1 Marshmallow, with its fresh "M" logo and simplified icons.
The first thing Lena noticed was Doze. The battery graph was a gentle slope, not a cliff. The second was App Permissions—no more flashlight apps asking for her contacts. The third, and most personal, was the Selfie Master app. The front camera’s 13MP sensor, now optimized for Marshmallow, captured skin tones that actually looked like skin.
She took a deep breath. The phone, once dead, was reborn.
That night, she wrote a new post on XDA: “Fixed my Z00UD. Don’t give up on your Selfie. Marshmallow is worth the nightmare.”
Her phone didn't just have new firmware. It had a second life. The notification arrived on a Tuesday, thin as
The End.
Meta Description: Looking for the official ASUS ZenFone Selfie Z00UD firmware 6.0.1? This guide covers download links, step-by-step installation, Android Marshmallow features, and fixes for common upgrade errors.