Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisHard
A technician is diagnosing an intermittent issue where a vehicle's power windows occasionally stop working. The technician observes that the windows sometimes work perfectly, and other times they are completely inoperative. When inoperative, neither the master switch nor individual door switches can operate the windows. All fuses are good. What is the MOST likely cause?
- AAn intermittent open in a door jamb switch
- BA faulty master power window switch module
- CAn intermittent open in the main power supply or ground to the window control module
- DA short to ground in a window motor circuit
Show answer & explanationAnswer & explanation
Correct answer: C. An intermittent open in the main power supply or ground to the window control module
If all windows become inoperative, and the master switch is also affected, it points to a common failure point. An intermittent open in the main power or ground supply to the entire window control module/system would cause all functions to fail intermittently, while individual switch or motor issues would typically affect only one window.
Why the other options are wrong
- A. An intermittent open in a door jamb switch would typically affect only related functions (e.g., dome light), not all power windows.
- B. While a faulty master switch could be a cause, if the individual door switches also fail to operate *any* window when the master fails, it suggests a more fundamental power or ground issue to the entire system, which the master switch relies upon.
- D. A short to ground in a single window motor circuit would likely blow a fuse or only affect that specific window, not all windows intermittently.
Common Power/Ground
A single power or ground connection that supplies multiple circuits or an entire system, making it a critical point of failure for all connected components.
- Failure affects multiple components/systems
- Often involves main fuses, relays, or ground points
- Important to check first for system-wide issues
Memory trick: When all goes dark, check the main spark.