Exact model-family answer directory

Samsung Galaxy S21 troubleshooting

Choose the symptom actually shown by SM-G991*. Current Galaxy family; confirm the complete SM identifier, region and One UI version before repair or firmware instructions. Error codes remain separate records because the same characters can mean different things on another platform.

battery drainnot chargingoverheatingWi-Fino serviceBluetooth

Reviewed records

18 exact answers

Not sure where the fault is?

Samsung · app crashing

Samsung Galaxy S21 app keeps crashing, freezing or will not open

For the Samsung Galaxy S21, one app versus the operating system, storage and service state determines the safe sequence.

Open record Samsung · battery drain

Samsung Galaxy S21 battery drains too quickly

For the Samsung Galaxy S21, recent update/indexing, screen/radio use, background activity, signal and battery condition should be measured before replacement.

Open record Samsung · biometric unlock

Samsung Galaxy S21 biometric unlock is not working

For the Samsung Galaxy S21, sensor obstruction, enrolled appearance/finger, protector, environment and hardware should be separated.

Open record Samsung · camera blurry

Samsung Galaxy S21 camera is blurry, shakes or will not focus

For the Samsung Galaxy S21, lens contamination, case magnets, one app/lens and camera hardware should be separated.

Open record Samsung · calls

Samsung Galaxy S21 cannot make calls or send messages

For the Samsung Galaxy S21, carrier service, selected line, account activation, recipient-specific block and messaging service should be separated.

Open record Samsung · overheating

Samsung Galaxy S21 gets hot or shows a temperature warning

For the Samsung Galaxy S21, high workload, charging, signal search, environment and a failing battery must be separated.

Open record Samsung · GPS

Samsung Galaxy S21 GPS or location is inaccurate

For the Samsung Galaxy S21, app permission, precise-location setting, outdoor satellite view, network assistance and sensor calibration should be separated.

Open record Samsung · no service

Samsung Galaxy S21 has no cellular service or data

For the Samsung Galaxy S21, carrier outage/account/provisioning, SIM/eSIM, coverage, line selection and device radio should be separated.

Open record Samsung · microphone

Samsung Galaxy S21 microphone is quiet, muffled or not working

For the Samsung Galaxy S21, different apps and call modes use different microphones.

Open record Samsung · notifications

Samsung Galaxy S21 notifications are delayed or missing

For the Samsung Galaxy S21, app permission, channel/category, Focus modes, background restriction, account sync and network should be separated.

Open record Samsung · not syncing

Samsung Galaxy S21 photos, contacts, messages or account data will not sync

For the Samsung Galaxy S21, account status, cloud capacity, network, permissions and local storage should be separated before sign-out.

Open record Samsung · touchscreen

Samsung Galaxy S21 screen or touch input is not working correctly

For the Samsung Galaxy S21, one app/region, moisture, protector/case, charger interference and display hardware should be separated.

Open record Samsung · update failed

Samsung Galaxy S21 software update will not download or install

For the Samsung Galaxy S21, eligibility, power, storage, network, date/time and update service should be checked before recovery.

Open record Samsung · speaker

Samsung Galaxy S21 speaker is quiet, distorted or has no sound

For the Samsung Galaxy S21, earpiece, loudspeaker, Bluetooth routing, app audio and obstruction should be separated.

Open record Samsung · storage full

Samsung Galaxy S21 storage is full or the device cannot install updates

For the Samsung Galaxy S21, large media, downloads, app caches and system-update reserve should be measured before deletion.

Open record Samsung · not charging

Samsung Galaxy S21 will not charge or charges slowly

For the Samsung Galaxy S21, power source, cable/adapter, port debris/liquid, temperature and battery protection should be separated.

Open record Samsung · Wi-Fi

Samsung Galaxy S21 will not connect to Wi-Fi or keeps disconnecting

For the Samsung Galaxy S21, one network, all networks, VPN/profile and radio hardware produce different fixes.

Open record Samsung · Bluetooth

Samsung Galaxy S21 will not pair or stay connected over Bluetooth

For the Samsung Galaxy S21, accessory pairing state, competing hosts, profile support and radio issues should be isolated.

Open record

Confirm the model first

Which units this covers, and how to tell yours is one of them

Every answer below is scoped to these model identifiers. A neighbouring model in the same line can use a different part, a different reset sequence or a different radio, so matching the identifier before following a procedure is the step that decides whether the rest of the page applies to you.

Model numbers and patterns: SM-G991*
What that covers: Current Galaxy family; confirm the complete SM identifier, region and One UI version before repair or firmware instructions.

Published specification

What is true of this model and changes how you fix it

These are the properties that decide which procedure applies. Each is read from the manufacturer’s own published figures for this model, not carried over from a sibling that shares its retail name.

Tier — flagship base (no S Pen): The compact older flagship, no S Pen, small battery. One UI over Android, nearing end of major updates.
eSIM + physical SIM, IP68: eSIM and physical SIM, IP68, fast + wireless charging.
Age: Battery ageing and end-of-major-updates are age factors, not faults.

Where these figures were read. samsung.com Galaxy S21 (flagship base, One UI), read 2026-09-01

Manufacturer support for this product line. Samsung Support — Mobile device support. Official Galaxy model manuals, diagnostics, updates and repair support.

Exact questions

Questions that only have an answer for the Samsung Galaxy S21

Each answer below uses this model’s own published figures. The same question asked about a different model in the line has a different answer, which is why it is answered here rather than on a general page.

My Galaxy S21 won't get the newest One UI/Android.+

The S21 has reached or is near the end of its major-update window (Samsung provided several years of OS upgrades plus extended security updates), so it may keep getting security patches but not the newest Android/One UI version. A missing newest feature is that support age, not a fault. Check Settings › Software update; if none appears, it has reached the end of its major-version support.

Structured depth, not empty permutations

Every published record carries a direct answer, scope, ordered fixes, risk notes and sources.

Device and manufacturer hubs share a consistent record system, but each answer carries the relevant controls, fault boundaries, consequences and official support entry point for that platform.

See the publication gate