During a visual inspection for an intermittent concern, a technician finds green corrosion and pitted terminals in a harness connector below the cowl, and the connector's weather seal is missing. What is the correct repair?

Replace the pitted terminals and install a new seal

Install a new seal and reuse the original terminals

Clean the terminals and coat them with dielectric grease

Replace the module that the connector supplies

What is the purpose of a diode connected across a relay's coil?

To clamp the coil's turn-off voltage spike

To raise the coil's pull-in current

To protect the coil from reversed battery polarity

To keep the switched contacts from arcing

Why is the negative battery cable disconnected before the positive cable when a battery is removed from a vehicle?

A wrench touching metal at the positive post cannot short the battery

The negative cable carries less current, so it sparks less when loosened

Module memory is held through the positive cable until it is removed

The negative cable's current sensor resets only if it loses power first

A battery removed from a vehicle stored for four months reads 11.6 volts open-circuit. On a charger set to the manufacturer's rate, the charger's voltage rises to its limit within minutes while the charging current stays near zero for two hours. Which of these is the most likely cause?

An open connector between two cells

A normal discharge needing more time

With the engine off, a vehicle's battery reads 12.3 volts. With the engine at 1,500 rpm and all loads off, the battery posts still read 12.3 volts, and so does the alternator output (B+) terminal. The belt is in good condition and turning the pulley. Which of these could be the cause?

Brushes worn so they no longer touch the slip rings

An open output fuse between the alternator and battery

Corrosion at the battery positive cable clamp

A pulley one-way clutch seized to the rotor shaft

A vehicle's turn signals use incandescent bulbs and an electronic flasher that senses lamp current and flashes at about twice the normal rate when the current is lower than normal. The left turn signals flash at the fast rate; the right turn signals flash at the normal rate. Which of these could be the cause?

An open filament in the left rear turn signal bulb

An open filament in the right rear turn signal bulb

A higher-wattage bulb installed in the left front socket

A failed timing circuit in the flasher unit

On this vehicle the heated mirrors are powered from the rear defogger relay's output. The rear window and both mirrors do not heat. The defogger indicator lights when the button is pressed, and scan data shows the body module commanding the defogger relay on. What should be checked next?

Voltage at the relay output and its feed fuse

Resistance of the grid lines on the rear glass

Resistance of the left mirror's heating element

Operation of the defogger request button

A driver's heated seat comes on, then shuts off within seconds and its indicator flashes. The seat module sends 5 volts through an internal resistor to the seat temperature sensor, whose resistance falls as it warms. With the seat at 70°F, scan data shows a seat temperature of 250°F. Which of these is the cause?

The sensor signal wire is shorted to ground

The sensor signal circuit is open at a terminal

The cushion heating element has an open

The heated seat switch contacts are worn

The manufacturer's hood-ajar switch closes to ground when the hood opens. With the hood open, the scan tool shows the hood as closed. With the switch unplugged and a jumper across the harness connector's signal and ground terminals, the scan tool shows the hood as open. This points to:

a faulty or misadjusted hood-ajar switch.

a fault in the module's hood-ajar input circuit.

an open in the switch's signal wire.

an open in the switch's ground wire.

10 Free ASE A6 Electrical/Electronic Systems Questions

Ten ASE A6 Electrical/Electronic Systems questions in the ASE format: four options, one best answer. They are free to use, print and share, and there is nothing to sign up for on this page.

01How to use these

The questions come from the ToolboxPrep A6 bank and are spread across the test's content areas in the proportion the ASE test specification gives them: A (General Electrical/Electronic System Diagnosis), B (Battery and Starting System Diagnosis and Repair), C (Charging System Diagnosis and Repair), D (Lighting Systems Diagnosis and Repair), E (Body Electrical Systems Diagnosis and Repair). Answer each one before opening the explanation. Every explanation covers all four options, because knowing why the wrong answers are wrong is most of the skill.

Pace. The A6 test gives you 90 minutes for 60 questions (50 scored, 10 unscored), about 1 min 30 s a question. Try these at that pace.
Print. The printed version shows the questions and the answer key without the explanations, so it works as a handout.

02The questions

Diagnosis · General Electrical/Electronic System Diagnosis

During a visual inspection for an intermittent concern, a technician finds green corrosion and pitted terminals in a harness connector below the cowl, and the connector's weather seal is missing. What is the correct repair?
1. Install a new seal and reuse the original terminals
2. Clean the terminals and coat them with dielectric grease
3. Replace the pitted terminals and install a new seal
4. Replace the module that the connector supplies
Show the answer

C. Correct. Pitted terminals have lost metal and contact pressure, so cleaning cannot restore them, and without the seal water will get in again. New terminals crimped and sealed as the manufacturer specifies, plus a new seal, fix both the fault and its cause.

Why not the others

A. The new seal stops further water entry, but the pitted terminals still make poor contact and the intermittent fault remains. The damaged terminals are replaced along with the seal.

B. Cleaning removes loose corrosion but cannot replace the metal pitting has eaten away, and grease does not stop water entering a connector with no seal. The damaged terminals are replaced and the seal is installed.

D. The fault found is in the connector, not the module; a new module plugged into the same corroded terminals would show the same concern. The terminals and the seal are repaired.
Recall · General Electrical/Electronic System Diagnosis

A module turns a solenoid on by grounding its control wire (a low-side driver). A lab scope on the control wire shows a pattern that repeats every 8 ms: the wire sits at 0 volts for 2 ms and at 13.8 volts for the rest of each cycle. What is the solenoid's on-time duty cycle?
1. 20%
2. 25%
3. 33%
4. 75%
Show the answer

B. Correct. With a low-side driver the solenoid is on while the control wire is pulled to 0 volts: 2 ms of every 8 ms cycle, so 2 / 8 = 25 %. The 13.8 volts is the solenoid feed showing through the switched-off winding.

Why not the others

A. This treats the 8 ms period as the off-time and adds the 2 ms to it (2 / 10 = 20 %). The whole cycle is 8 ms, so the on-time duty cycle is 2 / 8 = 25 %.

C. This divides the on-time by the off-time (2 / 6). Duty cycle is on-time divided by the whole cycle: 2 / 8 = 25 %.

D. This counts the 13.8-volt time as on (6 / 8). With a low-side driver the solenoid is on while the wire is at 0 volts, so the on-time is 2 of 8 ms, 25 %.
Recall · General Electrical/Electronic System Diagnosis

What is the purpose of a diode connected across a relay's coil?
1. To raise the coil's pull-in current
2. To protect the coil from reversed battery polarity
3. To keep the switched contacts from arcing
4. To clamp the coil's turn-off voltage spike
Show the answer

D. Correct. When coil current stops, the collapsing magnetic field induces a high voltage spike; the diode, reverse-biased in normal operation, conducts that spike back through the coil. This protects the switch or module transistor that controls the coil.

Why not the others

A. In normal operation the diode is reverse-biased and carries no current, so it does not change the coil's pull-in current. It conducts only the spike from the collapsing field when the coil turns off.

B. With reversed polarity the diode would be forward-biased and conduct directly across the coil's supply, so it offers no protection. The diode is there to clamp the spike from the coil's collapsing field.

C. The diode is across the coil, not across the switched contacts, so it does nothing for contact arcing. It clamps the voltage spike when the coil turns off.
Recall · Battery and Starting System Diagnosis and Repair

Why is the negative battery cable disconnected before the positive cable when a battery is removed from a vehicle?
1. The negative cable carries less current, so it sparks less when loosened
2. A wrench touching metal at the positive post cannot short the battery
3. Module memory is held through the positive cable until it is removed
4. The negative cable's current sensor resets only if it loses power first
Show the answer

B. Correct. The body and engine are connected to the battery negative post, so with the negative cable still attached a wrench that bridges the positive post to metal makes a dead short. Removing the ground cable first breaks that path; on reinstallation the positive cable goes on first and the negative cable last for the same reason.

Why not the others

A. The negative and positive cables are in series with the same loads, so they carry the same current. The order is chosen so that a wrench slipping from the positive post onto metal cannot short the battery, which is only true once the ground cable is off.

C. Removing either cable opens the circuit, so module memory is lost when the first cable comes off, whichever one it is; a memory saver is what keeps memory. The negative-first order is there to prevent a short through a wrench at the positive post.

D. A battery current sensor on the negative cable is not reset by the order the cables come off; some vehicles need a scan-tool registration step after a battery change instead. The negative cable comes off first so that a wrench at the positive post cannot short the battery to ground.
Diagnosis · Battery and Starting System Diagnosis and Repair

A battery removed from a vehicle stored for four months reads 11.6 volts open-circuit. On a charger set to the manufacturer's rate, the charger's voltage rises to its limit within minutes while the charging current stays near zero for two hours. Which of these is the most likely cause?
1. A shorted cell in the battery
2. Hard sulfation of the plates
3. An open connector between two cells
4. A normal discharge needing more time
Show the answer

B. Correct. A battery left discharged for months forms hard lead-sulfate crystals that resist current, so its voltage climbs to the charger's limit while it accepts almost no current. Some can be recovered with a charger mode the battery maker approves, but many must be replaced; retest after any recovery attempt.

Why not the others

A. A shorted cell lowers the battery's resistance, so it would take current readily while its voltage stayed low. Here the voltage rises at once and almost no current flows, which points to sulfated plates.

C. An open connection between cells breaks the circuit, so the battery would read near 0 volts at the terminals and pass no current at all. This battery reads 11.6 volts open-circuit, so the path through the cells is complete; the plates are sulfated.

D. A discharged battery in good condition accepts a high current at first, which tapers as it charges. Current that stays near zero while the voltage jumps to the charger's limit shows the plates cannot accept charge, the sign of hard sulfation.
Diagnosis · Charging System Diagnosis and Repair

With the engine off, a vehicle's battery reads 12.3 volts. With the engine at 1,500 rpm and all loads off, the battery posts still read 12.3 volts, and so does the alternator output (B+) terminal. The belt is in good condition and turning the pulley. Which of these could be the cause?
1. Brushes worn so they no longer touch the slip rings
2. An open output fuse between the alternator and battery
3. Corrosion at the battery positive cable clamp
4. A pulley one-way clutch seized to the rotor shaft
Show the answer

A. Correct. Neither reading rose above the engine-off voltage, so the alternator is making no output, and the equal readings show the output circuit still connects it to the battery. With the brushes off the slip rings no current reaches the rotor field, and a rotor with no magnetic field induces nothing in the stator however fast it spins.

Why not the others

B. An open output fuse would cut the B+ terminal off from the battery, so the terminal could not read the same 12.3 volts as the battery posts. Equal readings at both ends show the output circuit is intact; the alternator itself is making nothing.

C. A corroded clamp adds resistance between the alternator and battery, so a working alternator's B+ terminal would read higher than the battery posts. Here neither reading rose above the engine-off voltage, which means the alternator is producing no output at all.

D. A seized one-way clutch locks the pulley to the rotor shaft, so the belt still spins the rotor and the alternator still charges; it causes belt and tensioner vibration rather than a loss of output. Zero output with the belt driving the rotor points to the field circuit.
Diagnosis · Lighting Systems Diagnosis and Repair

A vehicle's turn signals use incandescent bulbs and an electronic flasher that senses lamp current and flashes at about twice the normal rate when the current is lower than normal. The left turn signals flash at the fast rate; the right turn signals flash at the normal rate. Which of these could be the cause?
1. An open filament in the right rear turn signal bulb
2. An open filament in the left rear turn signal bulb
3. A higher-wattage bulb installed in the left front socket
4. A failed timing circuit in the flasher unit
Show the answer

B. Correct. With one left bulb open, only the left front lamp draws current, so the flasher sees less current than two bulbs draw and switches to its fast rate. The right side still draws normal current and flashes normally; replace the open bulb and recheck.

Why not the others

A. An open right rear bulb would lower the current only while the right turn signal is on, so the right side would flash fast. Here the right side is normal and the left side is fast, which points to an open bulb on the left side.

C. A higher-wattage bulb draws more current, not less, so the flasher would not see the low current that triggers its fast rate. Low current on the left side comes from a lamp that is not drawing, such as an open filament in a left bulb.

D. The one flasher times both sides, so a timing fault would show on the left and right turn signals alike. Since the right side flashes normally, the flasher is responding correctly to low current on the left side.
Diagnosis · Body Electrical Systems Diagnosis and Repair

On this vehicle the heated mirrors are powered from the rear defogger relay's output. The rear window and both mirrors do not heat. The defogger indicator lights when the button is pressed, and scan data shows the body module commanding the defogger relay on. What should be checked next?
1. Resistance of the grid lines on the rear glass
2. Voltage at the relay output and its feed fuse
3. Resistance of the left mirror's heating element
4. Operation of the defogger request button
Show the answer

B. Correct. The module is commanding the relay on, yet three loads fed from the relay's output all fail together, so the common point is the relay's output side: its contacts and the fuse feeding them. Check for battery voltage at the relay output with the defogger switched on.

Why not the others

A. A grid fault would affect only the rear glass, and the mirrors fed from the same relay fail as well. Check the shared relay output and its fuse first.

C. One mirror element cannot stop the other mirror and the rear glass from heating. The three loads fail together, which points to the relay output they share.

D. The indicator lights and scan data show the module commanding the relay on, so the request from the button is getting through. The fault is after the command, at the relay output or its fuse.
Diagnosis · Body Electrical Systems Diagnosis and Repair

A driver's heated seat comes on, then shuts off within seconds and its indicator flashes. The seat module sends 5 volts through an internal resistor to the seat temperature sensor, whose resistance falls as it warms. With the seat at 70°F, scan data shows a seat temperature of 250°F. Which of these is the cause?
1. The sensor signal circuit is open at a terminal
2. The sensor signal wire is shorted to ground
3. The cushion heating element has an open
4. The heated seat switch contacts are worn
Show the answer

B. Correct. A short to ground pulls the signal to near 0 volts, which the module reads as a very low sensor resistance, the reading of a very hot seat. Seeing 250°F on a 70°F seat, the module treats it as an overheat, shuts the heater off and flags the fault.

Why not the others

A. An open signal circuit lets the signal rise to the full 5 volts, which the module reads as a very high resistance, a very cold seat. Scan data shows 250°F, the opposite, which is what a short to ground produces.

C. An open element would stop the seat from heating, but it would not change what the temperature sensor reports. The 250°F reading on a 70°F seat comes from the sensor signal being pulled to ground.

D. The heater comes on, so the module is receiving and acting on the request, and the switch is working. The shutdown follows the false 250°F sensor reading.
Diagnosis · Body Electrical Systems Diagnosis and Repair

The manufacturer's hood-ajar switch closes to ground when the hood opens. With the hood open, the scan tool shows the hood as closed. With the switch unplugged and a jumper across the harness connector's signal and ground terminals, the scan tool shows the hood as open. This points to:
1. a fault in the module's hood-ajar input circuit.
2. an open in the switch's signal wire.
3. an open in the switch's ground wire.
4. a faulty or misadjusted hood-ajar switch.
Show the answer

D. Correct. The jumper did the switch's job at the harness, and the module saw the hood as open, so the signal wire, the ground wire and the module's input all work. The switch is not closing when the hood opens, either from an internal fault or because its bracket keeps the plunger from extending.

Why not the others

A. The module reported the hood open as soon as the jumper grounded its input, so the input circuit works. The part that fails to ground the signal is the switch itself.

B. If the signal wire were open, jumpering at the switch connector could not reach the module, and the data would still read closed. It changed to open, so the signal wire is good.

C. The jumper ran from the signal terminal to the harness ground terminal, so it used that ground wire. The module saw the change, which proves the ground wire works and leaves the switch.

03Answer key

Question	Answer	Content area
Q1	C	General Electrical/Electronic System Diagnosis
Q2	B	General Electrical/Electronic System Diagnosis
Q3	D	General Electrical/Electronic System Diagnosis
Q4	B	Battery and Starting System Diagnosis and Repair
Q5	B	Battery and Starting System Diagnosis and Repair
Q6	A	Charging System Diagnosis and Repair
Q7	B	Lighting Systems Diagnosis and Repair
Q8	B	Body Electrical Systems Diagnosis and Repair
Q9	B	Body Electrical Systems Diagnosis and Repair
Q10	D	Body Electrical Systems Diagnosis and Repair

04Questions by content area

Working on one part of the A6 test? Each content area has its own page with five more free questions.

05More free questions

The A6 study guide covers each content area and how to study for it, and the ASE A6 Electrical/Electronic Systems practice test page describes the full A6 question bank. The same free format is available for the other eight tests.

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.