ASE Practice Test (A6: Electrical/Electronic Systems) 1 — Questions and Answers
Question 1: A circuit has a specified voltage drop of no more than 0.5 volts across a switch. The measured drop is 1.8 volts with the circuit loaded. This indicates:
- Normal reading for a high-current circuit
- Excessive resistance in the switch contacts (Correct answer)
- A short circuit to ground in the switch
- Incorrect meter polarity during testing
Correct answer: Excessive resistance in the switch contacts
Excessive voltage drop across a switch indicates high resistance at the contact points — often caused by corrosion, pitting, or loose connections. Voltage drop testing is the best method for finding resistance in a loaded circuit.
Question 2: A technician is testing a blower motor circuit. The motor runs slowly at all speeds. Using a voltmeter, full battery voltage is present at the motor connector with the switch in HIGH position. The MOST likely cause is:
- Faulty blower speed resistor
- High resistance in the ground circuit (Correct answer)
- Incorrect fuse rating in the circuit
- Open circuit in the blower relay
Correct answer: High resistance in the ground circuit
If full battery voltage is present at the motor but it still runs slowly, the problem is in the ground return path. Excessive resistance in the ground circuit restricts current flow, reducing motor speed. A faulty resistor would cause a no-operation condition at that speed, not slow operation at all speeds.
Question 3: When using an oscilloscope to test a crankshaft position sensor, the waveform shows a missing tooth pattern. This is:
- A sign of sensor failure requiring replacement
- Normal — the missing tooth is a reference gap for TDC (Correct answer)
- Evidence of electrical interference on the signal wire
- Caused by excessive air gap between sensor and reluctor
Correct answer: Normal — the missing tooth is a reference gap for TDC
Most crankshaft position sensor reluctor wheels have a missing tooth or gap machined into them as a reference point that the ECM uses to identify TDC (top dead center) for cylinder #1. This is by design and not a defect.
Question 4: A vehicle has an inoperative power window on the right rear door only. All other windows work normally. The MOST efficient first test would be:
- Replace the right rear window regulator motor
- Check for battery voltage and ground at the right rear window motor (Correct answer)
- Test the master switch on the driver's door
- Inspect the body control module for fault codes
Correct answer: Check for battery voltage and ground at the right rear window motor
When only one window is inoperative, the problem is isolated to that circuit. Checking for voltage and ground at the motor quickly determines if the issue is in the switch/wiring (no voltage) or the motor itself (voltage present but no movement).
Question 5: A diode in an alternator rectifier bridge is shorted. This will MOST likely cause:
- The alternator to produce no output voltage
- AC ripple voltage to appear on the DC output (Correct answer)
- The battery to overcharge above 15.5 volts
- Excessive field current draw
Correct answer: AC ripple voltage to appear on the DC output
A shorted diode in the rectifier bridge allows AC current to pass through rather than being blocked. This causes AC ripple to appear on the DC charging output, which can be detected with a voltmeter on AC setting or an oscilloscope. A reading above 0.5V AC indicates a bad diode.
Question 6: Technician A says a parasitic draw test should be performed with all doors closed and the vehicle in sleep mode. Technician B says a draw of 35 milliamps is acceptable on most modern vehicles. Who is correct?
- Technician A only
- Technician B only
- Both Technician A and Technician B (Correct answer)
- Neither Technician A nor Technician B
Correct answer: Both Technician A and Technician B
Both technicians are correct. The vehicle must be in sleep mode (all modules powered down) for an accurate parasitic draw test, which requires doors closed and a waiting period. Most manufacturers specify a maximum draw of 25–50 milliamps, making 35 mA an acceptable general threshold.
ASE Practice Test (A6: Electrical/Electronic Systems) 1
A circuit has a specified voltage drop of no more than 0.5 volts across a switch.
The measured drop is 1.8 volts with the circuit loaded.
This indicates: