How to Fix OPPO F21s Pro 4G Sim Card Not Detected

A SIM card is needed not only for mobile communication. She stores phone numbers, allows you to access the Internet (when connecting special tariffs), and in some cases also serves as a way to authorize the phone (PIN code for SIM cards). But sometimes OPPO F21s Pro 4G SIM card not detected for some reason:

1. Incorrectly inserted SIM card.
2. Malfunctions and defects of the SIM card or slot.
3. Problems with drivers.
4. Software issues.
5. The SIM card is not activated in the settings.

Let's take a closer look at each of them.

The reasons for the problem with the SIM card on OPPO F21s Pro 4G

Issues with SIM cards are divided into hardware and software.

To begin with, let's look at hardware issues.

Incorrectly inserted SIM card

There are currently two types of SIM cards in active use: Micro-sim and Nano-sim. The former is easily confused in size with SD cards. Because of this, sometimes the Micro-sim is placed in the slot for external memory and does not work. This issue is fixed by inserting the Micro-sim into the desired slot.

Nano-sim by size is small — if they are inserted incorrectly, the compartment with a place for the SIM card will still close, but the mobile connection will not work. The issue is also solved by the correct insertion of the Nano-sim.

Malfunctions and defects of the SIM card

The SIM card is damaged in several ways: incorrect circumcision scratches or furrows on the contacts, mechanical shocks, etc. There is one solution — replacement of the SIM card with a new one at the nearest branch of your operator.

Malfunctions and defects of the slot

The interaction of the SIM card with the OPPO F21s Pro 4G phone occurs through the contacts in the connector. Firstly, these contacts can oxidize when liquid gets on them. Secondly, the connector may break due to mechanical impact. Thirdly, the contacts and connector may become dirty over time if there are chips or cracks on the phone case.

It is difficult to solve the first two problems on your own — you need to disassemble the phone, check the operation of the circuits and, if necessary, replace broken parts. It is easier to give the device to a service center.

But, as for pollution, you can cope with them yourself:

1. Turn off the phone. We are waiting 5–10 minutes.
2. We dip a thin cotton swab in pure alcohol.
3. Wipe the contacts and connector through the outer hole with light movements without pressure.
4. We wait at least 1 hour, or until the alcohol dries.
5. Turning the phone back on.

If you are afraid to clean yourself, contact specialists. If the SIM card is not visible even after cleaning, and other methods did not help, take the smartphone to the service center.

Programmatic reasons include the following:

Problems with OPPO F21s Pro 4G phone drivers

Owners of new phones often face similar problems. Sometimes the manufacturer is in such a hurry to present a working model to the buyer that it does not prepare the operating system for full operation.

Software problems

In smartphones, separate programs are used for calls and messages. Sometimes, after the update, errors appear in them that do not allow you to identify the SIM card.

The SIM card is not activated in the settings

If the SIM card is no longer activated automatically, then:

1. Need to go to settings.
2. Item "Network and Internet".

3. Submenu "SIM card and mobile network".
4. In the "SIM card Information and Settings" menu, select the desired SIM card.
5. We turn the toggle switch opposite the "Activate SIM card" to the enabled position.
6. If the SIM card has become active, then your phone number will appear next to the "Number" item.

Checking the SIM card

Testing on another device

To check the SIM card, try inserting it into another smartphone. If it works, then errors occur on your device, and they are not related to the SIM card. In any case, remember that often the SIM card does not work simply because it was blocked by the mobile operator.

Checking for damage

It will also not hurt to inspect the SIM card for damage — scratches and chips immediately catch the eye.

What to do if OPPO F21s Pro 4G SIM card not detected

Rebooting the device

Software problems are sometimes solved by rebooting. To do this, follow these steps:

1. Hold the power button for 5–10 seconds.
2. A menu appears in which to select the "Restart" option.
3. Wait 1–2 minutes and check if the SIM card works.

Installing software updates

The SIM card may not work due to software errors. It is impossible to fix them yourself. The only option — wait until the software developer releases an update with bug fixes. They usually come out within a couple of hours, a maximum of several days. We have a separate material on how to update OPPO F21s Pro 4G so we will not dwell on this process in detail here.

Resetting network settings

This method is controversial since it does not solve the main problems with SIM cards. But if you decide to try it, then:

1. Go to settings.
2. Go to the "System" section.
3. Select the item "Resetting settings".
4. Select "Reset settings".
5. Click on "Reset settings".

Remember that resetting the settings deletes all network-related data. This also applies to Wi-Fi passwords and devices linked via Bluetooth.

Contacting the service center

If none of the described methods helped you, then just contact the service center. Firstly, this way you will absolve yourself of all responsibility. Secondly, professionals are more likely to be able to solve all your problems.

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