Hidden Android Diagnostic Menus & Codes to Test a Used Phone

A used Android phone can look flawless and still hide a dead pixel row, a lazy proximity sensor, a crackling earpiece or a modem that drops signal every few minutes. You won’t find those faults by scrolling the home screen for thirty seconds. You find them by asking the phone to test itself — and almost every Android maker ships a hidden diagnostic menu for exactly that purpose.

These menus were built for factory lines and repair technicians, which is why they’re reached through dialer codes instead of an icon. This guide explains which codes are universal, which belong to a single brand, what each screen actually tells you, and why some codes simply do nothing on certain phones.

How dialer codes work (and why some fail)

Android codes come in two shapes. Codes like *#06# are MMI codes defined by the mobile standards bodies, so the phone app handles them on any handset. Codes wrapped in *#*#…#*#* are different: the dialer broadcasts a “secret code” message to the system, and whatever app has registered for that number opens. If the manufacturer removed that app, the code does nothing.

That explains three things you’ll run into:

• Carrier firmware blocks codes. A US carrier-branded Galaxy often ignores *#0*# even though the same model bought unlocked responds instantly.
• The dialer matters. Some third-party dialers don’t pass secret codes to the system. Use the phone’s stock Phone app.
• No call button needed. Most codes trigger the moment you type the last character. If you have to press Call, it usually isn’t going to work.

Universal codes that work on almost every Android

*#06#
*#07#
*#*#4636#*#*

*#06# — the IMEI

This shows the IMEI (two of them on dual-SIM phones), and on recent devices the EID for eSIM too. It’s the number every serious check depends on, so compare it with Settings › About phone and the SIM tray label before anything else. If you’re new to it, start with what an IMEI number is.

*#07# — SAR information

On many phones this shows the specific absorption rate (SAR) values the model was certified with. It’s mostly interesting because a clone or relabeled phone often shows nothing, or values for a different model number than the one printed in Settings.

*#*#4636#*#* — the Testing menu

This is Android’s own testing screen, part of the platform rather than any brand. On Pixels, Motorola, Nokia and many other phones it opens a menu with Phone information, Usage statistics and Wi-Fi information. Samsung and some Chinese brands hide or strip it, so a non-response there is normal.

In Phone information, look at:

• Signal strength in dBm and ASU. On LTE, roughly −80 dBm is excellent, −100 dBm is usable and anything around −115 dBm or lower is weak. Compare with your own phone standing in the same spot — a 20 dB gap points to an antenna or modem problem.
• Voice and data network type. If it shows LTE or NR on your SIM, the radio accepts your carrier. “Unknown” or “Out of service” with a working SIM is a red flag.
• Preferred network type. Read it, don’t change it. Setting it wrong can leave the phone stuck on 2G.

Samsung: the *#0*# hardware test menu

Samsung’s hidden test menu is the most complete of any brand. Dial *#0*# and you get a grid of buttons:

*#0*#
*#12580*369#
*#0228#

• Red / Green / Blue / Black: full-screen colors. Look for dead pixels, green or pink lines, and burn-in ghosts (keyboard or status bar shapes) on the gray-ish tones. Black reveals light bleed and bright pixels.
• Receiver / Speaker: plays a tone through the earpiece and the loudspeaker. Listen for buzzing or a silent channel.
• Vibration: the motor should buzz evenly, not rattle.
• Sensor: live readings for the accelerometer, proximity and light sensors. Cover the top of the screen — proximity should flip immediately.
• Touch: draw across a grid of boxes. Any box that won’t fill is a dead zone in the digitizer.
• Mega cam / Front cam: opens the cameras directly to test focus and flash.

Press Back twice to leave. *#12580*369# displays software and hardware version information, and *#0228# opens a battery status screen on many Galaxy models. Both vary by model and firmware, so treat a non-response as normal.

The official, supported option is Samsung Members › Support › Phone diagnostics, which runs the same kinds of tests with pass/fail results, including battery status. Because the app is Samsung’s own, a seller can’t easily argue with it. Then confirm the hardware matches the paperwork with the Samsung Info report, which lists the model, region and warranty for the IMEI.

Google Pixel: built-in diagnostics without the hassle

Pixels lean on Settings rather than secret menus:

• Settings › Battery › Battery health on newer models shows an estimated capacity and, on some, the cycle count. Older Pixels show less.
• Settings › Battery › Battery diagnostics runs a guided battery test on supported models.
• Pixel diagnostic tool: on many recent Pixels, dialing *#*#7287#*#* opens Google’s diagnostic app with touch, display, speaker and sensor tests. If the code doesn’t respond, the app isn’t present on that build.
• *#*#4636#*#* works fully on Pixels and is the quickest signal check.

Pair the hardware checks with a Google Pixel Info check to confirm the exact model, carrier variant and warranty. Our Pixel carrier unlock guide explains why a locked Verizon Pixel behaves differently from an unlocked one.

Other brands: Xiaomi, Motorola, OnePlus

*#*#6484#*#*
*#*#2486#*#*
*#808#

• Xiaomi / Redmi / POCO — *#*#6484#*#*: opens the CIT hardware test menu, with tests for the display, touch, speakers, sensors, cameras and more. If the dialer ignores it, go to Settings › About phone › All specs and tap Kernel version five times. Then run a Xiaomi check to confirm Mi account and lost status.
• Motorola — *#*#2486#*#*: opens the CQATest menu on many Moto phones. The supported route is the preinstalled Device Help app, which includes device diagnosis. Cross-check the model with the Motorola Info check.
• OnePlus — *#808#: opened an engineering test mode on older OxygenOS builds. Newer versions based on ColorOS often ignore it; *#*#4636#*#* still works on many.

Expect variation. The same code can open a full menu on one firmware and do nothing after an update. Our OnePlus and Motorola buying guide covers the rest of the inspection for those brands.

A 10-minute test routine for a used Android

1. Dial *#06# and photograph the IMEI. Match it with Settings and the SIM tray.
2. Insert your SIM, open *#*#4636#*#* (or Settings › About › SIM status) and note the signal in dBm next to your own phone.
3. Run the brand test menu: display colors, touch grid, earpiece, speaker, vibration, proximity.
4. Test what menus can’t: make a real call, record a voice memo, take photos with every lens, plug in a charger and check it charges, try Wi-Fi and Bluetooth.
5. Check the battery: through the brand app or Settings; on any phone, the adb shell dumpsys battery command from our ADB inspection guide works.
6. Run the record checks on the IMEI: blacklist, model, carrier.

What diagnostic codes can’t tell you

A phone can pass every hardware test and still be a bad buy. Test menus don’t know whether the IMEI was reported stolen, whether the phone is financed, or whether the model is what the seller claims. A clone with a well-made fake “About phone” page will even pass a basic sensor test. Validate the IMEI below — type dial for every way to read it, then imei followed by the number to check its digit:

Then run a GSMA blacklist check and a manufacturer and model check to make sure the record matches the hardware. Our check-before-you-buy guide puts the whole process in order.

Verdict: hidden diagnostic menus are the fastest way to catch hardware faults a seller hopes you’ll miss — but they’re half the job. Hardware test plus an IMEI record check is what makes a used phone safe to buy.