Phone Secret Codes for Dead Pixel Testing
Most manufacturers hide a hardware diagnostic mode in their phones. These codes let you test the display at the hardware level — no app download needed.
What Are Phone Diagnostic Codes?
Phone manufacturers include hidden service menus for technicians to test hardware components. These are accessed by dialling specific codes in the Phone app or navigating through Settings. The display test shows solid colour screens — identical to this browser tool, but running at the hardware level without the OS layer above it.
Samsung: *#0*#
- Open the Phone app. Make sure you are on the Dialler tab (not Recent Calls).
- Type *#0*# — the diagnostic menu opens automatically. Do not tap the call button.
- Tap Red and inspect for any pixel that is not red.
- Tap Green and inspect for any pixel that is not green.
- Tap Blue and inspect for any pixel that is not blue.
- Tap Black and inspect for any bright or coloured dots (stuck pixels).
- Tap White and inspect for any dark dots (dead pixels).
- Press the back button to exit.
Works on: Galaxy S7 and later, Z Flip 4/5/6/7, Z Fold 4/5/6/7, Galaxy Note. May not work on A-series or Galaxy Watch.
Xiaomi: Settings Tap Method
- Go to Settings → About Phone.
- Tap Kernel Version exactly 5 times in quick succession (about 1 tap per second).
- A Hardware tests menu appears at the bottom of the About screen.
- Tap Display.
- Follow the on-screen instructions — tap through each solid colour and inspect.
Works on: MIUI 13/14 and HyperOS 1/2. May vary by firmware version.
Sony Xperia: *#*#7378423#*#*
- Open the Phone app and go to the dialler.
- Type *#*#7378423#*#* — the service menu opens automatically.
- Select Service tests → Display.
- Follow the prompts to test each colour.
Works on: most Sony Xperia models. Code may not work on all regional variants.
OnePlus and Google Pixel: Browser Test
Neither OnePlus nor Google Pixel phones have a built-in diagnostic code accessible from the dialler. Use this browser-based test — it is functionally equivalent and requires no download.
Tap anywhere to cycle colours · Long press for previous
How to Interpret Diagnostic Test Results
- Black screen — bright or coloured dot: Stuck pixel (lit sub-pixel that cannot turn off). May be fixable with the fix tool.
- White screen — dark dot: Dead pixel (emitter or transistor failure). Requires screen replacement.
- Red/Green/Blue screen — wrong colour dot: Stuck sub-pixel at the wrong colour. Try the fix tool.
- No defect found: Display passes. If you still suspect an issue, test at different brightness levels.
Frequently Asked Questions
What is *#0*# used for?
It's Samsung's hidden hardware diagnostic mode, accessible directly from the Phone app dialler. It bypasses the operating system to test hardware components — including the display — using solid colour screens.
Does *#0*# work on all Samsung phones?
It works on most Galaxy S-series (S7+), Z Flip, and Z Fold models running One UI. It typically does not work on Galaxy A-series budget phones or very old devices. Use this browser test as a fallback.
How do I exit the Samsung diagnostic mode?
Press the back button or the Home button to exit. If the screen is stuck on a solid colour, use the power button or volume buttons to navigate back.
Can I use Xiaomi diagnostic mode on Xiaomi Pad?
Yes. The Settings → About → Kernel Version tap method works on Xiaomi phones and Xiaomi Pad tablets running MIUI 14 or HyperOS.
What is the Sony Xperia diagnostic code?
Dial *#*#7378423#*#* in the Phone app. This opens the service test menu. Navigate to Display for the screen test.
Do diagnostic codes damage my phone?
No. These codes open read-only diagnostic tools that are built into the phone's firmware for service technician use. They do not modify any settings or data.