220-1101 Mobile Devices Practice Question
A user reports that their Android smartphone displays 'No SIM card - Emergency calls only' even though the SIM is properly inserted. The technician removes the SIM and inserts it into another compatible phone, where it works perfectly. The technician then inserts a known-working SIM from another phone into the original device, which still shows 'No SIM card.' Which of the following is the MOST likely cause?
⚠ Common exam trap
Test-takers frequently confuse a software or firmware issue (like baseband corruption) with a physical hardware fault, overlooking the simple diagnostic step of testing with a known-working SIM to isolate the problem to the device's SIM slot.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SIM slot contacts are damaged or dirty
Since the known-working SIM also fails in the original device, the fault is isolated to the device's SIM interface. Damaged or dirty SIM slot contacts can prevent the electrical connection needed for the phone to detect the SIM, even though the SIM itself is functional. This is the most likely cause because the SIM works in another phone and the original phone fails with any SIM.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The SIM card tray is upside down
Why it's wrong here
The SIM tray is mechanically keyed with an asymmetric notch, so inserting it upside down prevents it from seating flush or the SIM from aligning with the reader pins. A technician has already confirmed that the SIM is properly seated in the tray and the tray is correctly oriented, which rules out this user-error cause. Furthermore, a completely inverted tray would not close cleanly and would likely be immediately obvious, whereas this device reportedly closes normally.
- ✗
The IMEI number is corrupted in software
Why it's wrong here
A corrupted IMEI, typically stored in the device's NV/EFS partition, prevents the cellular baseband from identifying itself to the network, which can produce registration failures or 'no network' messages. However, it would still allow the phone to read the SIM card itself and display the IMEI as unknown or zero in settings. The 'No SIM card' alert specifically indicates that the phone is not detecting any electrical signal from a SIM, which is a hardware interface symptom rather than a software identity failure. Additionally, IMEI corruption would affect all SIMs, but that alone does not explain why a known-good SIM is also unrecognized at the physical layer.
- ✓
The SIM slot contacts are damaged or dirty
Why this is correct
The SIM slot consists of fragile spring-loaded contacts that press against the SIM's gold-plated pads; over time, these pins can bend, oxidize, or accumulate debris, breaking the electrical circuit. When that happens, the phone cannot perform the power-on reset sequence and will report 'No SIM card' even with a known-good SIM. Since two different SIMs fail identically, the fault is isolated to the phone's connector hardware, and cleaning or replacing the SIM reader is the correct repair. This also explains the 'emergency calls only' label, because the baseband is alive but never receives a SIM identity.
- ✗
The phone's baseband firmware needs to be updated
Why it's wrong here
Baseband (modem) firmware updates are meant to correct software-level issues like carrier aggregation bugs, VoLTE handovers, or radio power management quirks, but they cannot restore a broken electrical connection between the SIM and the phone. The 'No SIM card' error occurs before any baseband communication takes place — the phone's SIM interface controller never sees a valid Level-shifted signal. Because a known-good SIM fails identically, the issue is a hardware contact fault, not a software stack that needs reflashing. Updating the baseband would be a waste of time and could even introduce new incompatible settings.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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