220-1101 Hardware and Network Troubleshooting Practice Question
A user reports intermittent network connectivity on a desktop computer. The technician observes that the Ethernet link light on the NIC turns off for a few seconds and then turns back on. The cable passes a wiremap test, the switch port is verified good with another device, and the NIC driver is updated. The issue occurs more frequently when the computer's case fan runs at high speed. Which of the following is the MOST likely cause?
⚠ Common exam trap
Candidates often assume a failing NIC or cable fault when they see link drops, but the correlation with the case fan is the key clue that points to EMI, a classic CompTIA troubleshooting scenario.
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
✓
Electromagnetic interference from the case fan
The intermittent link light behavior, combined with the correlation to the case fan running at high speed, points to electromagnetic interference (EMI) from the fan motor. EMI can disrupt the electrical signals in the unshielded twisted-pair (UTP) cable, causing the NIC to lose link momentarily. Since the cable passes a wiremap test and the switch port works with another device, the issue is environmental, not a hardware fault.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Faulty NIC (Network Interface Card)
Why it's wrong here
A faulty NIC would typically produce consistent, persistent failures—complete link loss, high error counts, or a completely dead adapter—rather than a problem that reliably correlates with case fan speed. Because the symptom disappears when the fan slows down, it points to an external environmental factor affecting the Ethernet signal, not a defect within the NIC's own circuitry. Diagnostics would also likely show the NIC passing self-tests or loopback tests, further contradicting a hardware fault.
- ✓
Electromagnetic interference from the case fan
Why this is correct
A case fan's electric motor generates electromagnetic interference that intensifies with RPM, especially when PWM control changes the current spikes and commutation frequency. At high speeds, this EMI radiates into the nearby Ethernet cable, particularly unshielded twisted pair, and can overwhelm the differential signal the PHY expects. A loss of the link LED indicates the physical layer has lost a valid signal, which is precisely what happens when EMI injects enough noise to corrupt the link's energy detection. This is a classic scenario for transient link drops tied to fan speed.
- ✗
Incorrect pinout of the Ethernet cable
Why it's wrong here
A wiremap test validates that each conductor is terminated to the correct pin on both ends, which is the standard way to verify pinout. Since the cable passed this test, the T-568A/B pinout is confirmed correct, and an improper pinout cannot be the culprit. Even if a pinout error existed, it would usually cause the link to fail entirely or negotiate at a lower speed, not to drop intermittently in sync with fan speed. Therefore, this explanation is ruled out by direct evidence.
- ✗
Driver conflict with the fan controller
Why it's wrong here
Driver conflicts occur in software and can cause network interfaces to drop from the OS, but they cannot physically control the NIC's link LED, which is driven by the hardware's physical-layer transceiver. A fan controller is a separate hardware device with its own driver, and a software conflict between the two would not create a physical disturbance like electromagnetic interference. The symptom changes directly with fan speed—a physical event—so a software driver conflict would not produce such a tightly correlated hardware indicator as the link light turning off.
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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.