A vehicle's power windows operate slowly, and the radio occasionally cuts out when the windows are used. The battery tests good, and the charging system maintains 14.2 volts. What is the MOST likely cause of these symptoms?
- AA short circuit in the radio wiring.
- BA faulty window motor.
- CA failing body control module (BCM).
- DExcessive resistance in the main power feed to the accessory fuse box.
Show answer & explanationAnswer & explanation
Correct answer: D. Excessive resistance in the main power feed to the accessory fuse box.
Slow power window operation indicates high resistance in their circuit, causing a voltage drop. The radio cutting out simultaneously suggests a widespread voltage drop affecting other accessories, rather than a localized fault. If the battery and charging system are good, the problem is most likely in a common power supply path, such as the main power feed to the accessory fuse box where multiple high-current accessories (like power windows) draw their power. High resistance here would cause a voltage drop affecting all downstream components.
Why the other options are wrong
- A. A short circuit in the radio wiring would likely cause a blown fuse or constant power drain, not intermittent cut-outs specifically tied to window operation and slow window speed.
- B. A faulty window motor would primarily affect that specific window's speed, not cause the radio to cut out, unless it was drawing excessive current and causing a system-wide voltage drop at a critical point.
- C. While a BCM can cause various electrical issues, these specific symptoms (slow windows AND radio cut-out) point more directly to a shared power supply issue rather than a module logic fault, especially with a good battery and charging system.
Systemic Voltage Drop
Systemic voltage drop occurs when high resistance in a main power or ground path causes voltage to drop across multiple circuits simultaneously when a load is applied.
- Affects multiple, seemingly unrelated electrical components.
- Often traced to main power cables, ground straps, or primary fuse box feeds.
- Symptoms include dimming lights, slow motors, and electronic resets under load.
Memory trick: Many woes, one main flow's foes.