A6: Electrical & Electronic Systems (Sample Test)

The most likely reason a cooling fan motor keeps blowing the circuit fuse is a short to ground.

A short-to-ground happens when part of the electrical circuit unintentionally comes into contact with the vehicle’s chassis or ground. This often results from damaged wiring or a faulty component. When this occurs, it allows excessive current to flow through the circuit, overloading it and causing the fuse to blow repeatedly.

While other issues—such as an intermittent connection, an open circuit, or high resistance—can also affect the cooling fan motor, they are far less likely to cause the fuse to blow multiple times.

Technician A is correct in stating that the OBD II Data Link Connector (DLC) is located inside the vehicle, typically under the instrument panel on the driver’s side, within 2 feet of the steering wheel. This 16-pin standardized connector is used to interface diagnostic tools with the vehicle’s onboard computer systems.

Technician B is also correct. The Controller Area Network (CAN) bus, which links various electronic control units (ECUs), can be accessed through the OBD II connector. Using a diagnostic tool connected to the DLC, a technician can measure CAN bus resistance to check network integrity.

Therefore, both technicians have made accurate statements.

An open circuit at point B will prevent the spark plugs in cylinders #1 and #4 from firing, resulting in misfires in those cylinders. None of the other points would cause this specific issue.

Here’s why:

• Point A is the power supply to the ignition coil. If this circuit is open, the ignition coil won’t receive voltage, and none of the spark plugs will fire—not just #1 and #4.

• Point C is the ground for the ignition coil. An open at this point means the coil can’t complete the circuit, which also prevents all spark plugs from firing, not just specific ones.

• Point D is part of the secondary winding in the ignition coil. Excessive resistance here might weaken the spark, possibly causing intermittent misfires or poor performance, but it won’t completely stop the spark from occurring.

Therefore, only an open at point B, which affects the firing of cylinders #1 and #4 specifically, will lead to consistent misfiring in those two cylinders.

Power windows in a car are controlled by an electric motor located inside the door. This motor is connected to the window regulator—a mechanism made up of gears, cables, or linkages that raise and lower the window.

If the motor is faulty, it may not be able to move the window. Common causes include a burned-out winding, damaged gears, or a poor electrical connection. Any of these issues can prevent the motor from functioning properly.

To convert kilohms (kΩ) to ohms (Ω):

1 kΩ = 1000 Ω

So,
0.016 kΩ × 1000 = 16 Ω

Therefore, 0.016 kΩ equals 16 Ω.

The throttle position sensor (TPS) waveform is a valuable diagnostic tool that shows how the sensor is operating in real time. The TPS sends signals to the engine control module (ECM) indicating the position of the throttle plate, which helps the ECM adjust fuel delivery and ignition timing.

If the TPS is faulty—due to a worn sensor, erratic signal, or dead spots in the waveform—it can lead to engine performance problems such as hesitation during acceleration, poor throttle response, or stalling. Analyzing the waveform helps identify these issues and confirm whether the TPS is functioning correctly.

The inoperative lamp is the result of an open circuit between the switch and ground.

When the glove box is open and the switch is closed, a test light connected at point C illuminates. This confirms that the switch is working correctly and is supplying power to the circuit.

Since power is reaching point C, the issue is not due to:

• A burned-out bulb filament, or

• A short to ground at point D.

Therefore, the most likely cause is an open in the ground side of the circuit—specifically between the switch and the ground connection.

A faulty instrument panel voltage limiter is the most likely cause of all the gauges on the instrument panel reading at maximum output.

The voltage limiter regulates the voltage supplied to the gauges, ensuring they operate within safe limits. If it fails, excess voltage may reach the gauges, causing them to display abnormally high readings or remain pegged at maximum.

While other issues—such as a faulty ignition switch, loose instrument panel connector, or high charging system voltage—can also affect gauge operation, they are less likely to cause all gauges to spike at once. Additionally, high charging voltage would usually impact other vehicle electronics, not just the instrument cluster.

Both Technician A and Technician B are correct.

• Technician A is right in stating that a parasitic battery drain test is a good first step when diagnosing a battery drain issue. This test helps identify any electrical components that continue to draw power from the battery even when the vehicle is off.

• Technician B is also correct. A faulty alternator can contribute to battery drain—either by not charging the battery properly or by allowing current to leak back into the system when the engine is off.

The best diagnostic approach is to begin with the parasitic drain test as suggested by Technician A. If no abnormal current draw is found, then the alternator should be tested, as recommended by Technician B.

Technician A is correct. The aiming screen is the preferred method for headlight alignment, as it accommodates the wide range of modern headlight designs, including halogen, LED, and HID systems.

Technician B is incorrect. Mechanical aimers are outdated and not suitable for use with today’s headlight systems—especially HID headlights, which were never designed to be aligned using mechanical aimers.