220-1101 Mobile Devices Practice Question
A user reports that their Android smartphone's screen remains black during phone calls, even when the phone is held away from the ear. The screen works normally at all other times. The technician has already cleaned the top of the phone where the sensors are located and verified that the screen protector is not obstructing anything. Which of the following components is MOST likely causing the issue?
⚠ Common exam trap
It's easy for candidates to confuse the proximity sensor with the ambient light sensor, assuming both handle screen behavior during calls, but only the proximity sensor is responsible for toggling the display off when the phone is near the ear.
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
✓
Stuck or faulty proximity sensor
The proximity sensor is designed to detect when the phone is held to the ear and turn off the display to prevent accidental touches. If the sensor is stuck or faulty, it may continuously signal that the phone is against the ear, keeping the screen black even when held away. Cleaning the sensor and checking the screen protector are standard first steps, but if the issue persists, a defective proximity sensor is the most likely cause.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Failed ambient light sensor
Why it's wrong here
The ambient light sensor (ALS) measures ambient illuminance to adjust screen backlight levels; it has no connection to call-related screen on/off logic. In modern Android devices, the ALS only provides a value for automatic brightness; it never triggers the display to turn off. A failed ALS might cause a dim or overly bright screen, but during a call the screen would still remain on as long as the proximity sensor indicates 'far.' Therefore, an ALS fault cannot cause a black screen exclusively during calls.
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Corrupted display driver
Why it's wrong here
A corrupted display driver typically results in pervasive, persistent visual defects — flickering, static, distorted colors, tearing, or a completely unresponsive display — that occur regardless of the application or call state. The driver controls the entire display pipeline, so a malfunction would not selectively manifest only when a call is active. If the driver were the root cause, the screen would fail constantly or randomly, not in a consistent pattern tied to the call's near/far proximity state. Thus, a display driver issue is an implausible explanation for this call-specific symptom.
- ✓
Stuck or faulty proximity sensor
Why this is correct
The proximity sensor, usually an infrared transmitter/receiver, is designed to keep the screen dormant while the device is held against the ear. If the sensor is stuck in the 'near' state — due to a hardware fault, debris, a cracked display, or a faulty driver — the device continuously receives a 'near' reading and the LCD stays black after the call connects. This is the classic root cause of a screen that remains off during audio calls even after moving the phone away from your head. The Android telephony stack routinely polls this sensor; any failure in its measurement causes the display to remain locked in the 'off' state.
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Battery saver mode enabled
Why it's wrong here
Battery Saver mode reduces background activity, lowers CPU speeds, and sets a reduced screen brightness; it does not include any function to turn off the display during a call. Even with Battery Saver enabled, the proximity sensor still governs the screen's on/off behavior when a call is active. If the screen is black during a call, moving the phone away from the ear would still cause the display to light up, albeit possibly dimmed by the power-saving setting. Hence, battery saver is an unlikely cause unless accompanied by additional power-management bugs.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1101 exam.