22 A6 — Electrical / Electronic Systems Practice Questions & Answers

1. 1. A starter cable is suspected of unwanted resistance. Removed from the vehicle, it measures 0.2 ohm on an ohmmeter, which looks acceptable, yet the engine still cranks slowly. Why is a voltage-drop test taken while the engine cranks the better test?

   • A.A voltage-drop test reports the source voltage available at the load, which an ohmmeter cannot.
   • B.Resistance readings are valid only on a circuit that is energized and carrying its rated current.
   • C.Cranking pushes normal current through the fault, so even small resistance shows as lost voltage.✓ Answer
   • D.An ohmmeter cannot resolve values under one ohm, so any reading below that figure is meaningless.

   Unwanted resistance only reveals itself when normal current is flowing, because the voltage lost across it is the product of that current and the resistance. A few tenths of an ohm is invisible to an ohmmeter's tiny test current but loses well over a volt at cranking amperage, which is why voltage drop is always measured with the circuit loaded and operating.

   Source: ASE Automobile Study Guide, Test A6 task list, General Electrical/Electronic System Diagnosis (voltage-drop testing)Report a problem with this question

2. 2. To measure key-off battery drain, a technician disconnects the negative cable, connects a milliammeter in series with it, and immediately reads 1.8 A. What is the MOST likely explanation of that reading?

   • A.Modules woke when the cable was disconnected and have not timed out, so the reading came too early.✓ Answer
   • B.A dead short to ground exists, so fuses should be pulled one at a time to find it immediately.
   • C.The meter's internal fuse has opened, which makes an ammeter display a falsely high current value.
   • D.A shorted generator diode is feeding current backward, and that fault always reads close to 2 A.

   Disconnecting a cable wakes the network, and control modules commonly need a timed sleep interval before their draw falls to the normal key-off value. A reading taken before the modules time out measures wake-up current, not parasitic draw, so the technician must wait for the system to go to sleep and keep the circuit unbroken while connecting the meter.

   Source: ASE Automobile Study Guide, Test A6 task list, General Electrical/Electronic System Diagnosis (parasitic draw testing)Report a problem with this question

3. 3. A series circuit has a 12 V source and three resistors of 2 ohms, 4 ohms, and 6 ohms. Which statement about this circuit is correct?

   • A.Total resistance is about 1.1 ohms, so roughly 11 A flows and each resistor sees the full 12 V.
   • B.Current is 1 A throughout, and the 6 ohm resistor drops 6 V, the largest share of the source.✓ Answer
   • C.Current is 6 A at the source but 1 A at the 6 ohm resistor, since a larger resistor passes less.
   • D.Each resistor drops 4 V, because a series circuit splits the source voltage equally among loads.

   In a series circuit the resistances add, so total resistance is 12 ohms and current is 12 V divided by 12 ohms, or 1 A, and that same current flows through every component. Each voltage drop is then current times that resistor's value, giving 2 V, 4 V, and 6 V, which confirms the rule that the largest resistance drops the most voltage.

   Source: Ohm's Law and Kirchhoff's voltage law; ASE Automobile Study Guide, Test A6 task list, General Electrical/Electronic System DiagnosisReport a problem with this question

4. 4. Three lamps are connected in parallel across a 12 V supply and draw 2 A, 3 A, and 1 A. A fourth lamp is added in parallel with them. What happens to the circuit totals?

   • A.Total current stays at 6 A and total resistance rises, because source voltage has not changed.
   • B.Total resistance rises above 2 ohms and total current falls, as a new load shares the same 12 V.
   • C.Total current rises past 6 A and the total resistance drops below the previous 2 ohms figure.✓ Answer
   • D.Each original lamp now receives less than 12 V, so all three dim and total current drops.

   Branch currents add in a parallel circuit, so the original 6 A becomes more than 6 A once a fourth branch is added, while every branch still sees the full source voltage. Since total resistance equals source voltage divided by total current, 12 V over more than 6 A must be less than the 2 ohms the three lamps presented.

   Source: Parallel-circuit rules (branch currents add; total resistance is less than the smallest branch); ASE Test A6 task list, General Electrical/Electronic System DiagnosisReport a problem with this question

5. 5. A 15 A fuse for the power window circuit blows the instant the ignition is switched on. Which approach BEST isolates the short?

   • A.Fit a lamp or circuit breaker in place of the fuse and watch it as harness sections are unplugged.✓ Answer
   • B.Disconnect the battery and check each connector for continuity to ground with the loads still joined.
   • C.Install a 30 A fuse temporarily so the circuit stays alive long enough to read voltage at the motors.
   • D.Measure resistance from the fuse socket to ground with the battery connected and the switch closed.

   A lamp or a self-resetting breaker in the fuse socket carries the short current safely instead of destroying fuses, and it gives a live indication: the lamp glows brightly while the short is present and goes out the moment the faulted section is disconnected. Upsizing the fuse risks a harness fire, and resistance checks are invalid on a live circuit or when the load provides its own path to ground.

   Source: ASE Automobile Study Guide, Test A6 task list, General Electrical/Electronic System Diagnosis (circuit protection and short-to-ground diagnosis)Report a problem with this question

6. 6. The headlamps are on and dim. A DMM connected across the closed headlamp switch reads 4.6 V while battery voltage is 12.4 V. What does that reading indicate?

   • A.The switch contacts have high resistance and are using up voltage that belongs at the lamps.✓ Answer
   • B.The switch is normal, because closed contacts carrying current always show a few volts across them.
   • C.The lamp ground is open, which puts the entire source voltage across the switch contacts instead.
   • D.The switch is open, since a voltmeter placed across open contacts reads the full source voltage.

   A voltmeter connected in parallel with a component reads the voltage lost across it, not the voltage supplied to it. A good closed switch should drop only about a tenth of a volt, so 4.6 V means the contacts are resistive and the lamps are receiving roughly 4.6 V less than the source, which is exactly why they are dim.

   Source: ASE Automobile Study Guide, Test A6 task list, General Electrical/Electronic System Diagnosis (meter connection and voltage-drop interpretation)Report a problem with this question

7. 7. After surface charge is removed and the battery rests, open-circuit voltage measures 12.2 V at about 70 degrees F. What does that indicate and what should be done next?

   • A.Fully charged but sulfated; replace it, because a healthy battery rests at 13.2 V after charging.
   • B.Roughly three-quarters charged; the battery may be load tested at once with no recharging.
   • C.Fully discharged with a shorted cell; the battery will not accept a charge and must be replaced.
   • D.Roughly half charged; recharge it fully before judging it with a load or conductance test.✓ Answer

   On the industry state-of-charge scale a rested 12-volt battery reads about 12.6 V at full charge and roughly 12.2 V at half charge, so this battery is only partly charged. A capacity or load test performed on a partly charged battery will fail a good battery, so the correct sequence is to recharge fully and then test.

   Source: ASE Automobile Study Guide, Test A6 task list, Battery and Starting System Diagnosis and Repair (state of charge and battery testing)Report a problem with this question

8. 8. An engine cranks slowly. Starter current draw is well below the value given in service information, and battery voltage stays high while cranking. What is the MOST likely cause?

   • A.A dragging armature or tight engine bearings, forcing the starter motor to work much harder.
   • B.A battery with a shorted cell that cannot deliver the amperage the starter motor demands.
   • C.A shorted field winding inside the starter, letting current bypass part of the motor windings.
   • D.High resistance in the starter feed or ground path, limiting the current the motor can draw.✓ Answer

   Current draw that is low while cranking is slow points to something limiting current rather than something demanding it, and unwanted resistance in the cables, connections, or ground is the classic limiter. Mechanical drag or a binding starter would produce the opposite signature, high current draw with low cranking voltage.

   Source: ASE Automobile Study Guide, Test A6 task list, Battery and Starting System Diagnosis and Repair (starter current draw testing)Report a problem with this question

9. 9. A start-stop vehicle's AGM battery is replaced. Technician A says the new battery's type and rating must be registered or reset in the charging control system. Technician B says a conventional flooded battery of the same group size may be fitted with no other changes. Who is right?

   • A.Technician A only✓ Answer
   • B.Neither Technician A nor Technician B
   • C.Both Technician A and Technician B
   • D.Technician B only

   Vehicles that manage charging by battery type and age normally require the replacement to be registered or the battery monitoring data reset, or the control strategy will keep charging to the old battery's profile and either overcharge or undercharge the new one. Substituting a flooded battery for an AGM changes the charge acceptance and the vibration and cycling tolerance the system was designed around, so Technician B is wrong.

   Source: ASE Automobile Study Guide, Test A6 task list, Battery and Starting System Diagnosis and Repair (identify battery type and configuration; battery registration/reset after replacement)Report a problem with this question

10. 10. A tester's instructions call for loading a battery at half its cold cranking rating for 15 seconds, with a minimum of 9.6 V at 70 degrees F. A fully charged battery reads 9.1 V at the end of the 15 seconds. How should the result be read?

    • A.The battery is fine and the starter is at fault, because the drop appeared only under a load.
    • B.The test is invalid, since a battery has to be loaded to its full cold cranking rating to count.
    • C.The battery failed the test and should be replaced, since it was fully charged beforehand.✓ Answer
    • D.The battery passed, because anything above 9.0 V under load is acceptable at that temperature.

    The pass criterion supplied in the stem is the minimum voltage the battery must hold at the end of the applied load, and 9.1 V is below the stated 9.6 V minimum. Because the battery was already fully charged, a low state of charge cannot explain the result, so the battery itself lacks capacity and should be replaced.

    Source: ASE Automobile Study Guide, Test A6 task list, Battery and Starting System Diagnosis and Repair (battery capacity/load and conductance testing)Report a problem with this question

11. 11. With the engine at fast idle and the headlamps and blower on high, a DMM is connected with one lead on the generator B+ terminal and the other on the battery positive post. It reads 0.7 V. What does the reading mean?

    • A.The battery is weak and is pulling system voltage down, so it should be recharged and retested.
    • B.The insulated side of the charging circuit has excessive voltage drop between generator and battery.✓ Answer
    • C.Generator output is only 0.7 V, so the generator has failed internally and must be replaced.
    • D.This is normal rectifier ripple and shows that the diodes in the generator are within limits.

    Both meter leads are on the same conductor path, one at each end, so the meter is reading the difference between the two points rather than either point's voltage to ground. That difference is the voltage lost in the wire, connections, and any fusible link between them, and a loaded charging circuit should lose only a few tenths of a volt on the insulated side.

    Source: ASE Automobile Study Guide, Test A6 task list, Charging System Diagnosis and Repair (charging circuit voltage drop testing)Report a problem with this question

12. 12. A customer has replaced several batteries and reports a sulfur odor. System voltage measures a steady 15.8 V at idle and at speed with the lights on. What is the MOST likely cause?

    • A.A parasitic drain, which holds the generator at full field output to replace the lost charge.
    • B.A slipping drive belt, which lets the generator overspeed and raise its output voltage.
    • C.An open rectifier diode, which raises output because fewer diodes now share the current.
    • D.A faulty regulator or a resistive sense circuit that reports system voltage as lower than it is.✓ Answer

    Charging voltage held well above the normal range boils electrolyte, which is what produces the sulfur smell and the short battery life. The regulator controls output by comparing sensed voltage to a target, so either a failed regulator or resistance in the sense circuit makes the system believe voltage is low and keep raising field current.

    Source: ASE Automobile Study Guide, Test A6 task list, Charging System Diagnosis and Repair (overcharge diagnosis, regulator and voltage-sense circuits)Report a problem with this question

13. 13. Incandescent turn signal bulbs have been replaced with LED units. Both sides now flash rapidly and the driver information display shows a lamp outage message. What explains this and corrects it?

    • A.Fast flashing on both sides always means a failed flasher, so replacing the flasher unit clears the message.
    • B.The LEDs draw more current than the flasher can pass, so a heavy duty relay and larger feed wire are needed.
    • C.The LED drivers add ground-side resistance, so cleaning and regrounding every socket restores the flash rate.
    • D.The LEDs draw far less current, so the load-sensing flasher reads an outage; add resistors or an LED module.✓ Answer

    Load-sensitive flashers and bulb outage monitors decide a lamp has failed by watching how much current the circuit draws, and an LED draws a small fraction of the incandescent bulb it replaced. Restoring the expected load with resistors, or fitting hardware designed to expect LED current, is what makes the flash rate and the outage monitor behave normally again.

    Source: ASE Automobile Study Guide, Test A6 task list, Lighting Systems Diagnosis and Repair (turn signal and lamp outage diagnosis)Report a problem with this question

14. 14. With the right turn signal operating, the right taillamp and right brake lamp glow dimly and pulse with the signal. The left side behaves normally. What is the MOST likely cause?

    • A.A failed flasher unit that is sending pulsed voltage into the brake lamp circuit at the stop switch.
    • B.A short to voltage between the turn signal and brake lamp feeds, somewhere ahead of the lamp sockets.
    • C.An open or corroded ground shared by the right rear lamps, letting current backfeed through filaments.✓ Answer
    • D.Wrong wattage bulbs on the right side, overloading the feed and lighting the neighboring filaments.

    When the ground for a group of lamps is lost, current entering through the energized filament looks for a return path and finds one through the filaments of the other lamps sharing that ground. Those filaments then carry current in series with the intended lamp, which lights them dimly and in step with the circuit that is switched on.

    Source: ASE Automobile Study Guide, Test A6 task list, Lighting Systems Diagnosis and Repair (exterior lighting circuit and ground diagnosis)Report a problem with this question

15. 15. Both headlamps are dim and yellowish at idle and at road speed. The bulbs are new, and the battery and charging voltage test good. What is the MOST likely cause?

    • A.A shorted headlamp relay coil, which lowers the voltage the switch is able to deliver to the lamps.
    • B.An open low beam filament in one lamp, which cuts the current available to the remaining lamp.
    • C.Unwanted resistance in the feed or ground shared by both lamps, reducing the current through them.✓ Answer
    • D.Bulbs of lower wattage than specified, which draw less current and burn with a much whiter light.

    Two lamps dimming together points to something they have in common rather than to either lamp, and the shared feed or ground connection is that common element. Resistance there drops part of the source voltage before it reaches the bulbs, so the filaments run cooler and shift toward yellow, which a voltage-drop test on the headlamp circuit will confirm.

    Source: ASE Automobile Study Guide, Test A6 task list, Lighting Systems Diagnosis and Repair (headlamp circuit diagnosis)Report a problem with this question

16. 16. All of these are correct practices when removing a driver's airbag module EXCEPT:

    • A.Waiting the interval given in service information after the battery is disconnected before removal.
    • B.Carrying the module with its trim cover facing away from you and laying it face up on the bench.
    • C.Following the manufacturer's disable procedure and confirming no restraint codes remain stored.
    • D.Checking the inflator's deployment loop with an ohmmeter to prove continuity before reinstalling.✓ Answer

    An ohmmeter passes current through whatever it is connected to, and the current from an ordinary meter can be enough to fire an inflator, so a deployment loop or squib is never checked with an ohmmeter. The other three practices are standard: observe the specified wait time, keep the trim cover pointed away from you, and use the manufacturer's disable procedure.

    Source: ASE Automobile Study Guide, Test A6 task list, Body Electrical Systems Diagnosis and Repair (supplemental restraint system service precautions)Report a problem with this question

17. 17. After a steering column repair, the restraint warning lamp stays on, the horn does not work, and the steering wheel audio buttons are dead. What is the MOST likely cause?

    • A.A blown restraint system fuse, which also protects the horn relay and the audio switch circuit.
    • B.A failed body control module, which powers every steering wheel switch through a single driver.
    • C.A steering angle sensor out of calibration, which disables the wheel controls until it is relearned.
    • D.A torn or open clockspring, which carries the airbag, horn, and switch circuits through the column.✓ Answer

    The clockspring is the flexible ribbon that keeps electrical continuity between the fixed column and the rotating wheel, and it normally carries the driver airbag, horn, and steering wheel switch circuits together. Losing all three functions at once right after column work points to a ribbon that was torn because the clockspring was not centered before assembly.

    Source: ASE Automobile Study Guide, Test A6 task list, Body Electrical Systems Diagnosis and Repair (clockspring service and steering wheel controls)Report a problem with this question

18. 18. The right front window runs up and down normally from its own door switch, but from the driver's master switch it only goes down. What is the MOST likely cause?

    • A.An open contact in the master switch for the up direction, which is what reverses motor polarity.✓ Answer
    • B.An engaged window lockout function, which blocks the up command sent from the master switch.
    • C.A failed window motor whose brushes make contact in only one direction of armature rotation.
    • D.An open in the motor feed wire running between the master switch and the passenger door switch.

    A window motor is reversed by swapping the polarity applied to its two leads, and each switch does that with its own set of contacts. Because the same motor and the same feed wires work correctly from the passenger switch, the motor and wiring are proved good and the fault has to be in the contact set the master switch uses for the up direction.

    Source: ASE Automobile Study Guide, Test A6 task list, Body Electrical Systems Diagnosis and Repair (power window circuit diagnosis)Report a problem with this question

19. 19. With the rear window defogger on and the meter's negative lead grounded, a voltmeter reads about 12 V along the first half of one grid line and near 0 V along the rest of it. What does that show?

    • A.The grid line is broken at the point where the reading changes abruptly from source to zero.✓ Answer
    • B.The line is normal, since a grid line reads source at one end and zero volts at the other end.
    • C.The defogger ground is open, because every point on a good line should read half of source.
    • D.The feed side solder tab is loose, which is why part of that line reads zero volts to ground.

    A working grid line is a continuous resistance, so voltage measured to ground should fall gradually along it, passing through roughly half of source near the middle. A reading that holds at source and then jumps to zero means no current is flowing past that point, which locates the break exactly where the voltage changes.

    Source: ASE Automobile Study Guide, Test A6 task list, Body Electrical Systems Diagnosis and Repair (rear window defogger grid testing)Report a problem with this question

20. 20. A temperature gauge reads at the top of its scale while the engine runs at normal temperature, and a scan tool shows the coolant temperature PID at 195 degrees F with no driveability complaint. What should the technician suspect?

    • A.The thermostat, because the gauge is reporting a real overheat that the scan tool did not detect.
    • B.The coolant temperature sensor, because a gauge reading high always means a failed sending unit.
    • C.The cluster or the network message path, since the PID proves the sensor data itself is correct.✓ Answer
    • D.The engine ground strap, because the sending unit needs the cluster's ground to read accurately.

    On a networked vehicle the gauge does not read the sensor directly; a module measures the sensor and sends the value as a bus message that the cluster displays. A correct PID with a wrong needle position means the measured data is good and the fault lies downstream, in the cluster or in the message path, so replacing the sender would not fix anything.

    Source: ASE Automobile Study Guide, Test A6 task list, Body Electrical Systems Diagnosis and Repair (instrument cluster, gauges and driver information)Report a problem with this question

21. 21. An engine cranks at normal speed but does not start. The security indicator flashes, and a scan tool shows no injector pulse during cranking. What is the MOST likely cause?

    • A.The crankshaft position sensor is shorted to ground, which is what flashes the security lamp.
    • B.The immobilizer did not recognize the key, so the system is disabling delivery of fuel.✓ Answer
    • C.Battery voltage is under the module's operating threshold, which shuts off injector operation.
    • D.The starter control circuit is open, which keeps the engine from reaching normal crank speed.

    A flashing security indicator together with normal cranking and no injector pulse is the signature of an anti-theft disable: the immobilizer failed to authenticate the key, so the control module withholds the fuel or ignition function while everything else works. Normal cranking speed also rules out the starter control circuit and low battery voltage as explanations.

    Source: ASE Automobile Study Guide, Test A6 task list, Body Electrical Systems Diagnosis and Repair (anti-theft and immobilizer system diagnosis)Report a problem with this question

22. 22. The driver's door window, outside mirror, and door lock all quit at the same time, and the fault comes and goes as the door is opened and closed. What is the MOST likely cause?

    • A.A failed door module, which would drop all three functions regardless of door position.
    • B.A chafed or broken wire in the door harness where it flexes inside the jamb boot.✓ Answer
    • C.A corroded window motor ground, which the mirror and the lock actuator also depend on.
    • D.A weak battery whose voltage sags below the module's minimum whenever a motor runs.

    Several unrelated devices in one door failing together points to something they share, which is the power, ground, or data feed passing through the door jamb, and the fact that the symptom changes as the door moves points to a conductor that is being flexed. Wires inside the jamb boot fatigue and break there, so the circuit makes and loses contact with door position.

    Source: ASE Automobile Study Guide, Test A6 task list, Body Electrical Systems Diagnosis and Repair (body electrical circuit and intermittent diagnosis)Report a problem with this question

Practice questions written to the ASE Automobile & Light Truck (A-series) task lists and standard automotive service principles. ASE is a mark of the National Institute for Automotive Service Excellence; this site is not affiliated with or endorsed by ASE. Always follow the vehicle manufacturer's service information for specifications and procedures on a real repair. About the ASE tests →