Which statement indicates a DC heater malfunction?

• A. 1 only
• B. 2 only
• C. Neither
• D. 1 and 2 Both

Answer: (D)

Diagnosing a DC heater fault using two independent indicators is tested here. When both indicators show abnormal results, it strongly points to a malfunction in the heater circuit because two separate checks agree that something isn’t right. Each indicator reflects a different aspect of the heater’s operation, so if they both signal a problem, the likelihood of a true fault is high and it’s reasonable to conclude the heater is malfunctioning. If only one indicator were off, that single sign could be due to a sensor issue or a transient condition, and wouldn’t by itself confirm a true heater fault. Therefore, having both indicators indicate a problem is the most reliable confirmation of a malfunction.