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220-1201 Practice Question: A user's Android phone will not charge when…
A user's Android phone will not charge when plugged into a car's USB port, but charges fine with a wall adapter. The car's USB port powers other devices. What is the most likely issue?
⚠ Common exam trap
It's easy for candidates to assume any USB port that powers other devices must be capable of charging any phone, but the CompTIA A+ 220-1201 exam tests the distinction between USB port types (SDP vs. DCP) and the current negotiation required for modern smartphones.
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 car USB port does not supply enough current.
The car's USB port likely follows the USB Battery Charging Specification (BCS) 1.2, which defines a Dedicated Charging Port (DCP) as capable of supplying up to 1.5 A. However, many car USB ports are designed only for data transfer and provide a standard downstream port (SDP) limited to 500 mA (USB 2.0) or 900 mA (USB 3.0). The phone's charging circuit detects the available current via USB data line handshaking; if the port cannot supply enough current, the phone may refuse to charge or charge very slowly. Since the wall adapter provides adequate current (typically 1–2 A), the phone charges normally, isolating the issue to insufficient current from the car's port.
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 car's USB port is faulty.
Why it's wrong here
A faulty car USB port would typically exhibit complete power failure, intermittent connectivity, or physical damage, preventing any device from drawing power or establishing a stable connection. Since the port successfully powers other devices, it demonstrates basic functionality, indicating the problem is not a fundamental hardware defect. The issue is a limitation in its power delivery capabilities for the specific demands of the Android phone, rather than a complete malfunction.
- ✗
The phone's USB port is damaged.
Why it's wrong here
The phone's USB port cannot be the source of the problem because the device successfully charges when connected to a standard wall adapter. If the phone's physical port were damaged, obstructed, or internally compromised, it would consistently fail to charge regardless of the power source used. This successful charging with an alternative, known-good power supply confirms the phone's port is fully functional and not the cause of the car charging issue.
- ✓
The car USB port does not supply enough current.
Why this is correct
Modern Android smartphones often require a minimum current of 1 Ampere (A) or more to initiate and sustain charging, especially while the device is in use. Many older or standard car USB ports are designed primarily for data transfer or low-power accessories, typically supplying only 0.5A (500mA) at 5V. This insufficient current means the phone detects power but not enough to actively charge its battery, leading to the observed behavior where it appears not to charge.
- ✗
The USB cable is incompatible.
Why it's wrong here
The USB cable's compatibility or integrity is not the issue, as the problem statement indicates the same cable successfully charges the phone when connected to a wall adapter. If the cable itself were faulty, damaged, or incompatible with the phone's charging protocol, it would consistently fail to provide power across all charging scenarios. Its proven functionality with another power source eliminates it as the specific cause of the car charging failure.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1201 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 220-1201 exam.