Five free practice questions on charging systems: content area C of the ASE A6 Electrical/Electronic Systems test, 5 of its 50 scored questions (10%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.
01The questions
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During a current output test, the technician wants one reading that includes all the current the alternator delivers: the current charging the battery plus the current the vehicle's own loads are using. Where should the inductive amp clamp go?
- Around the negative battery cable
- Around the alternator output (B+) cable
- Around the alternator field-control wire
- Around the engine-to-body ground strap
Show the answer
B. Correct. Everything the alternator produces leaves through its output cable before the current divides between the battery and the vehicle's loads, so a clamp there reads total output. A carbon pile then loads the system so the reading shows the maximum the alternator can deliver.
Why not the others
A. The negative battery cable carries only the current that passes through the battery posts: the battery's own charge or discharge current, plus a carbon pile's if one is clamped to the posts. Current the alternator sends to the vehicle's loads returns through the engine and body grounds to the alternator housing without passing through that cable.
C. The field wire carries only the rotor's field current, a small fraction of the output it controls. Total output is read at the alternator output cable.
D. The ground strap carries only the share of the return current whose path happens to cross it, which depends on where the battery and each load are grounded; it never carries all of the output. The one place all the output passes is the alternator output cable.
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Any of these could cause an undercharge, with charging voltage at the battery below specification, EXCEPT:
- resistance in the regulator's battery-sense lead.
- an open diode in the rectifier bridge.
- brushes worn to the point of poor slip-ring contact.
- a glazed drive belt slipping on the pulley.
Show the answer
A. Correct. A regulator that reads battery voltage through a sense lead sees less than the true voltage when that lead has resistance, so it raises field current and pushes the charging voltage up. Resistance in the sense circuit points toward an overcharge, not an undercharge.
Why not the others
B. An open diode removes part of the rectified output, so the alternator cannot supply full current and the charging voltage sags under load. It is a real cause of undercharge.
C. Worn brushes pass less current to the rotor field, weakening its magnetism and the voltage the stator can produce. It is a real cause of undercharge.
D. A slipping belt turns the rotor slower than the pulley ratio intends, especially under load, so output falls and the battery voltage drops. It is a real cause of undercharge.
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A vehicle with an overrunning (one-way clutch) alternator pulley has low charging output. With the belt removed and the rotor shaft held with a holding tool, the pulley spins freely in both directions. What does this result show?
- The clutch has seized solid on the rotor shaft.
- The clutch is working normally in both directions.
- The clutch is slipping in its drive direction.
- The rotor shaft bearings have worn loose.
Show the answer
C. Correct. The one-way clutch should lock when the pulley is turned in the belt's drive direction and freewheel only the other way. Spinning freely both ways means it no longer drives the rotor properly, so the alternator turns slower than the belt and output falls. The pulley, or the alternator if the pulley is not sold separately, is replaced.
Why not the others
A. A seized clutch locks the pulley to the shaft in both directions, so with the shaft held the pulley would not turn at all. This one turns freely both ways.
B. The clutch is built to freewheel in one direction only, letting the rotor coast when the engine slows; in the other direction it must lock and drive the rotor.
D. Worn bearings show up as noise or shaft play; with the shaft held still they cannot let the pulley spin freely around it. The free spin is in the pulley's clutch.
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On many PCM-controlled charging systems, a monitor circuit carries a signal from the alternator's regulator back to the PCM. What does that signal report?
- The battery temperature used to set charging voltage
- The field duty cycle the regulator is applying
- The current flowing into or out of the battery
- The voltage the PCM wants the regulator to hold
Show the answer
B. Correct. The regulator reports the share of time it is switching the field on; a high figure means the alternator is working near its limit. The PCM uses it to judge electrical load and to detect a charging fault.
Why not the others
A. Battery temperature comes from a temperature sensor or a module's estimate, not from the regulator's monitor circuit, which reports the field duty cycle.
C. Battery current is measured by a current sensor on a battery cable. The regulator's monitor circuit reports the field duty cycle.
D. That is the command signal, which travels the other way, from the PCM to the regulator. The monitor circuit carries the regulator's field duty cycle back to the PCM.
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During alternator replacement, what should be done before loosening the nut on the alternator's output (B+) terminal?
- Turn the ignition off and remove the key
- Disconnect the negative battery cable
- Unplug the alternator's regulator connector
- Release the tensioner and remove the belt
Show the answer
B. Correct. The output terminal is connected to the battery at all times, ignition on or off, so a wrench that touches ground while on that nut shorts the battery through the tool. With the negative cable off, the circuit is open and the terminal is safe to work on.
Why not the others
A. The output terminal is wired straight to the battery, often through a high-current fuse, not through the ignition switch, so it stays live with the key out. The negative battery cable is disconnected first.
C. The regulator connector carries control circuits; unplugging it leaves the output terminal connected to the battery and live. The negative battery cable is disconnected first.
D. Removing the belt is part of the job but does nothing electrically, so the output terminal remains live. The negative battery cable comes off before the output nut is loosened.
02Answer key
| Question | Answer |
|---|---|
| Q1 | B |
| Q2 | A |
| Q3 | C |
| Q4 | B |
| Q5 | B |
03What area C covers
This content area covers the charging system: the alternator and its pulley, the drive belt and tensioner, voltage and current output tests, regulators and PCM charging control, voltage drop on the output and ground circuits, and the wiring and connectors between the alternator and the battery. It runs from diagnosing no-charge, undercharge and overcharge complaints to replacing the alternator.
The ASE test specification calls this content area “Charging System Diagnosis and Repair”. It carries 5 of the 50 scored questions, 10% of the test.
- Diagnose no-charge, low-charge and overcharge conditions
- Inspect belts, pulleys, tensioners and pulley alignment
- Run charging voltage and current output tests
- Test regulators, sensors and PCM charging control
- Voltage drop test the output and ground circuits
- Repair charging circuit wiring and terminals
- Remove and replace the alternator
04What the questions turn on
Low output with ripple
Each rectifier diode passes part of the stator's output. With one open, part of the wave is missing, so output falls and the voltage carries a large AC ripple. Low output with high ripple points to the rectifier or a stator winding.
Where the regulator senses voltage
Resistance in a regulator's battery-sense lead makes it see less than true voltage, so it pushes charging voltage up. A regulator that senses at its own output terminal cannot see a bad output cable, and the battery is left undercharged.
Test with a charged battery
A deeply discharged battery draws heavy charging current and holds the voltage down, so a good alternator can read low. The battery is charged and tested before the alternator is judged, and charging voltage is read at the battery posts.
Pulleys set alternator speed
Alternator speed is engine speed times the pulley ratio. A larger alternator pulley turns the rotor slower, so a unit can pass at 2,000 rpm yet fall behind at idle. An overrunning pulley that spins freely both ways also cuts output.
05The other content areas
The A6 test has five content areas. Each has its own page of free questions:
The ASE A6 Electrical/Electronic Systems practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.
ToolboxPrep is an independent study site. It is not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original practice questions written to the published ASE test specifications; they are not actual test questions.