Question 141 of 1,020

Mobile Device Connection Methods →easyMultiple ChoiceObjective-mapped

Phone Not Charging in Car USB Port: Current Supply Problems

This 220-1201 practice question tests your understanding of mobile device connection methods. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

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?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The car's USB port is faulty.
Why wrong: The port powers other devices, so it is functional; the issue is current output, not a fault.
B
The phone's USB port is damaged.
Why wrong: The phone charges with a wall adapter, so its port is working correctly.
C
The car USB port does not supply enough current.
Car USB ports typically output 0.5A, while modern phones may need 1A or more to charge; insufficient current prevents charging.
D
The USB cable is incompatible.
Why wrong: The same cable works with a wall adapter, so the cable is not the problem.

Full breakdown with real-world context →

Quick Answer

The answer is that the car USB port does not supply enough current. This is the most likely issue because car USB ports, especially older or standard models, often deliver only 0.5 amps, while modern Android phones require higher amperage—typically 1.0 to 2.4 amps—to initiate or sustain charging. Even if the port powers other devices like a GPS or a USB fan, those gadgets may draw less current, so the phone’s charging circuit simply refuses to accept the insufficient power, resulting in no charge at all. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of power specifications and current draw under the mobile device troubleshooting domain; a common trap is assuming the port is broken because it works with other devices. Remember the memory tip: “Amps are the flow, not the voltage—if the phone won’t go, the current’s too low.”

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.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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
The port powers other devices, so it is functional; the issue is current output, not a fault.
✗
The phone's USB port is damaged.
Why it's wrong here
The phone charges with a wall adapter, so its port is working correctly.
✓
The car USB port does not supply enough current.
Why this is correct
Car USB ports typically output 0.5A, while modern phones may need 1A or more to charge; insufficient current prevents charging.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The USB cable is incompatible.
Why it's wrong here
The same cable works with a wall adapter, so the cable is not the problem.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates 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.

Trap categories for this question

Command / output trap
The port powers other devices, so it is functional; the issue is current output, not a fault.

Detailed technical explanation

How to think about this question

The USB Battery Charging Specification 1.2 defines three port types: Standard Downstream Port (SDP, max 500 mA), Charging Downstream Port (CDP, up to 1.5 A with data), and Dedicated Charging Port (DCP, up to 1.5 A without data). Many car USB ports are SDPs designed for media playback, not charging, so they cannot negotiate higher current. In practice, some phones implement a 'USB current limit' that caps charging at 500 mA when connected to an SDP, leading to extremely slow or no charging if the device's power management requires more.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A practitioner preparing for the 220-1201 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 220-1201 question test?

Mobile Device Connection Methods — This question tests Mobile Device Connection Methods — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: 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.

What should I do if I get this 220-1201 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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