ASE A1 Engine RepairEngine Electrical Systems (General)Hard
A vehicle owner complains that their car's headlights dim noticeably when they press the brake pedal, and the engine occasionally stalls at idle. The battery tests good, and the charging system output is within specifications at higher RPMs. What is the MOST likely cause of these symptoms?
- AAn intermittent camshaft position (CMP) sensor failure.
- BA failing alternator voltage regulator.
- CA loose or corroded ground connection.
- DA faulty engine coolant temperature (ECT) sensor.
Show answer & explanationAnswer & explanation
Correct answer: C. A loose or corroded ground connection.
Intermittent electrical issues like dimming lights with load (brakes) and engine stalling, even with a good battery and charging system, are classic symptoms of a poor ground connection. A weak ground can cause voltage drops and erratic electrical behavior, especially under increased current draw.
Why the other options are wrong
- A. An intermittent CMP sensor would primarily cause starting issues, misfires, or stalling due to incorrect engine timing, but it wouldn't typically manifest as dimming headlights with brake application.
- B. A failing voltage regulator would typically lead to overcharging or undercharging the battery, which would be evident in the charging system output at various RPMs, not just dimming lights with specific electrical loads.
- D. An ECT sensor issue would primarily affect fuel mixture and engine performance, not cause dimming lights with brake application or directly cause stalls in this manner.
Ground Connection Importance
A good ground connection is essential for the proper operation of all electrical components in a vehicle, providing a low-resistance path for current to return to the battery.
- Poor grounds cause voltage drops and erratic electrical behavior.
- Can affect multiple systems simultaneously.
- Often overlooked in diagnostics.
Memory trick: Ghostly dimming? Check the 'Ground' for a shocking finding!