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ASE S6 Electrical/Electronic Systems (School Bus) study materials
ASE S6 Electrical/Electronic Systems (School Bus) study resources

ASE S6 Electrical/Electronic Systems (School Bus) practice questions

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Question 1General Electrical/Electronic System Diagnosis

A school bus has a single battery that keeps going dead overnight. A parasitic draw test shows 250 mA after all modules have gone to sleep. Which is the most appropriate next step?

  1. Install a larger alternator to keep up with the draw
  2. Replace the battery and retest in the morning
  3. Disconnect the battery cable and check for AC ripple
  4. Measure voltage drop across each fuse while pulling fuses one at a time Correct answer.

Explanation

A normal parasitic draw after sleep is typically well under 50 mA, so 250 mA indicates a fault. Measuring voltage drop across fuses (or current across them with an ammeter) localizes the circuit without disturbing module sleep. Replacing parts or adding charging capacity does not diagnose the source of the draw.

Question 2General Electrical/Electronic System Diagnosis

Which instrument is best suited for measuring current in a circuit without opening the conductor?

  1. Clamp-on ammeter Correct answer.
  2. Ohmmeter
  3. Test light
  4. Digital voltmeter

Explanation

A clamp-on ammeter senses the magnetic field around a conductor, allowing current measurement without breaking the circuit. A voltmeter measures potential difference and requires parallel connection. An ohmmeter requires the circuit to be de-energized and disconnected.

Question 3General Electrical/Electronic System Diagnosis

A technician measures 12.6 V at the battery posts but only 11.9 V at the starter solenoid stud while cranking. What does this indicate?

  1. A defective voltage regulator
  2. Normal operation because the solenoid is a load
  3. Excessive voltage drop in the cable or connections between battery and solenoid Correct answer.
  4. An open field circuit in the alternator

Explanation

Voltage lost between the source and the load represents resistance in the path. A drop of about 0.7 V under cranking load exceeds acceptable limits and points to cable, terminal, or ground resistance. The regulator and alternator field are not involved in cranking current delivery.

Question 4General Electrical/Electronic System Diagnosis

Before performing resistance tests on a vehicle circuit, the technician should:

  1. Disconnect power and isolate the circuit being tested Correct answer.
  2. Set the meter to the highest DC voltage range
  3. Turn on all accessories to load the circuit
  4. Start the engine to stabilize system voltage

Explanation

Resistance measurement requires no external voltage in the circuit, so power must be removed and the component isolated. Otherwise the meter's small test current is corrupted and readings are invalid. Loading or running the engine is appropriate for voltage-drop testing, not resistance.

Question 5General Electrical/Electronic System Diagnosis

A technician wants to confirm that a ground connection is sound on a body-mounted module. Which test gives the most reliable result?

  1. Verify battery voltage at the module power pin
  2. Measure resistance from the module case to the frame with the key off
  3. Measure voltage drop from the module ground pin to the battery negative post while the circuit is loaded Correct answer.
  4. Check for continuity from the ground pin to any nearby metal

Explanation

Voltage-drop testing under load reveals resistance that a low-current ohmmeter cannot detect. Measuring from the module ground to the battery negative post with current flowing shows the true voltage lost in the ground path. Continuity and unloaded resistance readings can pass even when the ground is inadequate under load.

Question 6General Electrical/Electronic System Diagnosis

Which condition most commonly causes a slow, intermittent drain that appears only after the vehicle has been parked for several hours?

  1. A module that fails to enter sleep mode Correct answer.
  2. A loose alternator belt
  3. A weak battery hold-down clamp
  4. A blown fuse in the charging circuit

Explanation

Modules that do not go to sleep continue to draw current after the key-off timer expires, producing a slow drain. This shows up only after the vehicle sits long enough for the battery to lose charge. Mechanical items like belts or clamps do not cause electrical drains.

Question 7General Electrical/Electronic System Diagnosis

A 12-volt system reading of 2.1 volts on a single battery in a two-battery parallel pack while the other reads 12.5 volts suggests:

  1. Normal equalization between parallel batteries
  2. An open in the cranking circuit
  3. A shorted cell or internally failed battery Correct answer.
  4. A faulty alternator diode trio

Explanation

Parallel batteries should rest at nearly equal voltage. A large difference, especially a very low reading, points to an internally failed or shorted battery. The alternator and cranking circuit do not explain a resting voltage imbalance between parallel batteries.

Question 8General Electrical/Electronic System Diagnosis

When using a test light to check a fused circuit, the light glows dimly when connected across the fuse terminals. What does this indicate?

  1. The fuse is open and the circuit has a load on the far side Correct answer.
  2. The fuse is good and passing full current
  3. The circuit is completely open with no load
  4. The test light bulb is the wrong rating

Explanation

A dim glow across a fuse means voltage is reaching the test light through the fuse's open element and continuing through downstream loads to ground. If the fuse were intact, both terminals would be at the same potential and the lamp would not light. A completely open circuit with no load would not complete a path for the lamp.

Question 9General Electrical/Electronic System Diagnosis

Which statement correctly describes the relationship between voltage, current, and resistance in a DC circuit?

  1. Voltage increases as resistance decreases at constant current
  2. Current increases as voltage decreases when resistance is constant
  3. Current increases as resistance decreases when voltage is constant Correct answer.
  4. Resistance increases as current increases at constant voltage

Explanation

Ohm's law states I = V/R, so with voltage fixed, lowering resistance raises current. The other relationships invert or misstate the law. This principle guides diagnosis of shorts and excessive loads.

Question 10General Electrical/Electronic System Diagnosis

A technician reads 0.00 ohms between a wire end and chassis ground on a circuit that should be isolated from ground. What is the most likely condition?

  1. An open circuit in the wire
  2. High resistance at a connector
  3. A short to ground in the wire or component Correct answer.
  4. Normal continuity through the load

Explanation

Near-zero resistance to ground on an isolated circuit indicates the conductor is touching ground, creating a short. An open would read infinite resistance, and a normal load would show some resistance rather than zero. High resistance would read above the expected value, not zero.

Question 11General Electrical/Electronic System Diagnosis

A school bus intermittently loses all dash cluster illumination when the headlights are turned on. Which diagnostic approach is most efficient?

  1. Add a ground strap from the cluster to the frame
  2. Monitor voltage at the cluster illumination feed while flexing the harness and operating the switch Correct answer.
  3. Replace the headlight switch first
  4. Replace the cluster and recheck

Explanation

Intermittent faults are best isolated by monitoring the affected circuit while reproducing the condition. Flexing the harness and cycling the switch helps localize an intermittent connection. Parts substitution and adding grounds do not confirm the fault location.

Question 12General Electrical/Electronic System Diagnosis

Which meter function would a technician select to verify that a diode in an alternator rectifier conducts in only one direction?

  1. Diode test mode Correct answer.
  2. DC volts
  3. Duty cycle
  4. Frequency (Hz)

Explanation

Diode test mode applies a small forward voltage and displays the drop, confirming one-way conduction. Voltage, frequency, and duty-cycle functions do not directly test junction behavior. A good diode shows a forward drop but blocks reverse current.

Question 13General Electrical/Electronic System Diagnosis

A technician is checking for excessive resistance in a starter ground path. The specification allows a maximum 0.2 V drop. The meter reads 0.45 V while cranking. What is the correct interpretation?

  1. The ground path exceeds specification and requires repair Correct answer.
  2. The starter is drawing too little current
  3. The meter is reading charging voltage
  4. The reading is acceptable because it is under 1 volt

Explanation

Comparing the measured drop to the published specification is the basis for pass/fail judgment. At 0.45 V the circuit exceeds the 0.2 V limit, indicating excessive resistance in the ground path. The other interpretations ignore the stated specification.

Question 14General Electrical/Electronic System Diagnosis

Which practice protects a digital multimeter when measuring current in an unknown circuit?

  1. Start on the lowest current range and step up
  2. Select the ohms range first
  3. Start on the highest current range and step down Correct answer.
  4. Leave the leads in the voltage jacks

Explanation

Starting on the highest current range prevents blowing the meter's internal fuse or damaging the shunt when actual current exceeds expectations. You can then step down for resolution. Leaving leads in voltage jacks or selecting ohms will not measure current correctly and may damage the meter.

Question 15General Electrical/Electronic System Diagnosis

A voltage is present at a component's power wire, but the component does not operate and its ground wire shows battery voltage when measured to ground. What does this indicate?

  1. Normal operation of a switched ground circuit
  2. A defective component relay coil
  3. A shorted power feed to the component
  4. An open ground path for that component Correct answer.

Explanation

If the ground wire reads battery voltage, the ground return is not completing the circuit, so the ground side floats up to supply potential. The component cannot operate without a complete path. A shorted feed or relay coil would not produce this specific symptom.

Question 16General Electrical/Electronic System Diagnosis

Which condition would cause a fuse to blow repeatedly immediately after replacement?

  1. A loose fuse holder terminal
  2. High resistance in the load
  3. A weak battery
  4. A direct short to ground on the protected circuit Correct answer.

Explanation

A fuse opens from excessive current, most often a direct short that bypasses the load. Repeated blowing right after replacement confirms a persistent high-current fault. Loose terminals, high resistance, and a weak battery cause low current or voltage issues, not repeated fuse failure.

Question 17General Electrical/Electronic System Diagnosis

A technician needs to locate an intermittent open in a long body harness. Which method is most effective?

  1. Measure resistance once with the harness at rest
  2. Perform a wiggle test while monitoring continuity or voltage drop across the circuit Correct answer.
  3. Replace the entire harness
  4. Check the battery state of charge

Explanation

Intermittent opens appear only when the conductor is disturbed, so flexing the harness while monitoring the circuit reproduces the fault. A single static resistance reading can miss an intermittent. Harness replacement and battery checks do not localize the fault.

Question 18General Electrical/Electronic System Diagnosis

What is the primary purpose of a wiring diagram during electrical diagnosis?

  1. To show hydraulic routing in the brake system
  2. To identify circuit paths, connectors, and shared grounds for a system Correct answer.
  3. To provide torque specifications for fasteners
  4. To list maintenance intervals for the vehicle

Explanation

Wiring diagrams map conductors, connectors, splices, and grounds so the technician can trace current paths and plan tests. They do not provide maintenance schedules, fastener torque, or hydraulic routing. Accurate diagram use prevents misdiagnosis of shared circuits.

Question 19General Electrical/Electronic System Diagnosis

Two modules share a common ground splice. One module works and the other does not, and voltage-drop testing shows high resistance only on the non-working module's branch. What is the most likely cause?

  1. A failed splice affecting both modules
  2. A defective battery ground cable
  3. A shorted power feed to the working module
  4. A poor connection in that module's branch between the splice and the module Correct answer.

Explanation

Because one module on the same splice works, the splice and main ground are likely intact. High drop confined to the non-working branch points to resistance in that branch's connector or wire. A failed splice or main cable would affect both modules.

Question 20General Electrical/Electronic System Diagnosis

A technician measures 14.2 volts at the battery with the engine running and all accessories off. This reading indicates:

  1. The regulator has failed open
  2. The battery is deeply discharged
  3. The alternator is overcharging the battery
  4. The charging system is operating within a typical range Correct answer.

Explanation

A charging voltage around 13.5 to 14.5 volts at the battery is typical for a 12-volt system. The reading is neither overcharging nor a sign of regulator failure. Battery state of charge is assessed separately.

Question 21General Electrical/Electronic System Diagnosis

During a voltage-drop test on a charging circuit, the technician measures 0.6 V from the alternator output stud to the battery positive post. What does this suggest?

  1. The alternator is undercharging by design
  2. The battery is fully charged
  3. Excessive resistance in the charging cable or connections Correct answer.
  4. Normal drop for a charging circuit

Explanation

Charging circuit voltage drop should generally be under about 0.3 V; 0.6 V indicates resistance in the cable or connections. This resistance reduces charge reaching the battery. Normal design and battery state of charge do not explain the excessive drop.

Question 22General Electrical/Electronic System Diagnosis

A relay in a school bus circuit clicks but the load does not operate. Which test should be performed first?

  1. Measure resistance of the load to ground
  2. Check the relay coil resistance
  3. Replace the relay
  4. Check for voltage at the load side of the relay contacts when energized Correct answer.

Explanation

A clicking relay shows the coil is energizing, so the next step is verifying whether the contacts are passing voltage to the load. This separates a contact fault from a downstream wiring or load fault. Replacing the relay or checking coil resistance skips the most direct test.

Question 23General Electrical/Electronic System Diagnosis

A technician observes that a circuit's measured resistance is far lower than the component's specified resistance, with the component disconnected. What is the most likely explanation?

  1. The meter leads are reversed
  2. The component is open internally
  3. The battery is disconnected
  4. An unintended parallel path exists in the circuit Correct answer.

Explanation

Lower-than-specified resistance with the component isolated suggests current is finding an alternate path, such as a chafed wire bridging to another conductor. An open component would read infinite resistance. Lead polarity and battery disconnection do not lower resistance readings.

Question 24General Electrical/Electronic System Diagnosis

Which safety practice applies when diagnosing a high-current circuit such as a starter feed on a school bus?

  1. Bypass fuses to speed testing
  2. Test with bare hands for heat
  3. Disconnect the battery only after cranking
  4. Remove metal jewelry and use insulated tools Correct answer.

Explanation

High-current circuits can cause severe burns and arc flashes, so removing conductive jewelry and using insulated tools reduces injury risk. Disconnecting after cranking or testing by touch is unsafe, and bypassing fuses removes circuit protection.

Question 25Battery Diagnosis and Service

A school bus battery is rated 12 volts with six cells. What nominal voltage does each cell contribute?

  1. 1.5 volts
  2. 12.0 volts
  3. 6.0 volts
  4. 2.1 volts Correct answer.

Explanation

A lead-acid cell produces about 2.1 volts at full charge, so six cells in series give roughly 12.6 volts at rest. The cell voltage is fixed by the lead-acid chemistry, not by the total battery rating.

Question 26Battery Diagnosis and Service

Which battery rating indicates the current a battery can deliver for 30 seconds at 0 degrees F while staying above 7.2 volts?

  1. Cranking amps
  2. Cold cranking amps Correct answer.
  3. Ampere-hour capacity
  4. Reserve capacity

Explanation

Cold cranking amps (CCA) is defined by a 30-second discharge at 0 degrees F with the battery held above 7.2 volts. Cranking amps uses the same 30-second and 7.2-volt criteria but at 32 degrees F.

Question 27Battery Diagnosis and Service

A bus battery reads 12.4 volts with the engine off and all loads removed. What does this indicate?

  1. A shorted cell
  2. Fully charged at 100 percent
  3. Surface charge present
  4. About 50 percent state of charge Correct answer.

Explanation

Open-circuit voltage tracks state of charge: about 12.6 volts is fully charged and 12.4 volts corresponds to roughly half charge. A shorted cell would pull the reading near 10.5 volts.

Question 28Battery Diagnosis and Service

Before performing a load test on a battery that was just removed from a charger, what should the technician do first?

  1. Remove the surface charge Correct answer.
  2. Apply a carbon pile load immediately
  3. Check the electrolyte color
  4. Add distilled water

Explanation

Charging leaves a surface charge that inflates voltage and masks the true condition. Applying a load or letting the battery rest removes that surface charge so the test is valid.

Question 29Battery Diagnosis and Service

During a capacity test, a battery fails to hold voltage under load but recovers to normal open-circuit voltage after resting. What is the most likely condition?

  1. Overcharged electrolyte
  2. High internal resistance Correct answer.
  3. Normal battery behavior
  4. Loose terminal

Explanation

A battery with high internal resistance collapses under load but rebounds to a normal open-circuit reading once the load is removed. The recovery is the key clue that separates it from a deeply discharged battery.

Question 30Battery Diagnosis and Service

What is the purpose of the battery hold-down bracket on a school bus battery?

  1. To measure current draw
  2. To secure the battery and reduce vibration damage Correct answer.
  3. To insulate the case
  4. To boost charging voltage

Explanation

The hold-down keeps the battery from shifting, which prevents case cracks, plate damage, and cable strain. It does not affect charging or current measurement.

Question 31Battery Diagnosis and Service

A technician connects a battery load tester and the voltage drops to 9.0 volts while cranking amps are applied. What does this most likely indicate?

  1. Battery has excessive water
  2. Battery is overcharged
  3. Battery is good
  4. Battery is sulfated Correct answer.

Explanation

A battery that falls well below the pass threshold under a rated load is typically sulfated or worn out and cannot deliver cranking current. Sulfation reduces active plate surface and raises internal resistance.

Question 32Battery Diagnosis and Service

Which condition causes a battery to self-discharge while sitting unused on the shelf?

  1. Low ambient temperature
  2. Dirty or wet case top Correct answer.
  3. New electrolyte
  4. Clean dry terminals

Explanation

Dirt and moisture on the case top create a conductive path between the terminals, causing parasitic self-discharge. Keeping the case clean and dry prevents this.

Question 33Battery Diagnosis and Service

While charging a battery, a technician notices it gassing heavily and the electrolyte level dropping. What is the most likely cause?

  1. Battery is cold
  2. Alternator is undercharging
  3. Battery is sulfated
  4. Charge rate too high Correct answer.

Explanation

Excessive gassing and water loss during charging point to an over-high charge rate, which electrolyzes water. The charge rate should be reduced to avoid plate damage.

Question 34Battery Diagnosis and Service

Which safety practice is required when jump-starting a school bus battery?

  1. Leave the engine running during connection
  2. Connect positive to negative
  3. Connect negative last to the good battery
  4. Connect the final negative connection to a ground away from the battery Correct answer.

Explanation

The final negative connection should be made to a solid engine or chassis ground away from the battery to keep sparks away from hydrogen gas. The positive cable connects first to the positive terminal.

Question 35Battery Diagnosis and Service

A bus has a parasitic draw that drains the battery overnight. Which test best isolates the circuit causing the drain?

  1. Load test the battery
  2. Check charging voltage
  3. Measure current with an ammeter and pull fuses one at a time Correct answer.
  4. Hydrometer test

Explanation

Measuring current draw and pulling fuses one at a time identifies the circuit responsible when the current drops. This isolates the parasitic load without guessing.

Question 36Battery Diagnosis and Service

What does a hydrometer reading of 1.265 specific gravity in all cells indicate?

  1. Discharged battery
  2. Shorted cell
  3. Fully charged battery Correct answer.
  4. Frozen electrolyte

Explanation

Specific gravity around 1.265 at 80 degrees F corresponds to a fully charged lead-acid cell. A discharged cell reads closer to 1.120.

Question 37Battery Diagnosis and Service

A hydrometer test shows one cell at 1.150 while the other five read 1.260. What does this indicate?

  1. Overcharged battery
  2. A defective cell Correct answer.
  3. Normal variation
  4. Surface charge

Explanation

A single cell reading far below the others indicates a defective or shorted cell. Because cells are in series, one weak cell limits the whole battery.

Question 38Battery Diagnosis and Service

What is the correct terminal connection order when installing a battery in a bus with a negative ground system?

  1. Connect both at the same time
  2. Positive first, then negative Correct answer.
  3. Either order is fine
  4. Negative first, then positive

Explanation

Connecting the positive cable first and the negative last reduces the chance of a short through the wrench to ground. Removal follows the reverse order.

Question 39Battery Diagnosis and Service

A technician finds white powdery corrosion on a battery terminal. What is the best service procedure?

  1. Clean the terminal and post, then apply protective coating Correct answer.
  2. Replace the battery
  3. Coat the terminal with grease and leave it
  4. Rinse with water only

Explanation

Corrosion should be cleaned from the post and clamp to restore a low-resistance connection, then a protective coating prevents recurrence. Leaving corrosion increases resistance and charging problems.

Question 40Battery Diagnosis and Service

A bus battery repeatedly goes dead, but the alternator tests good and the battery passes a load test. What should the technician check next?

  1. Alternator belt tension
  2. Starter draw
  3. Battery specific gravity
  4. Parasitic current draw Correct answer.

Explanation

When the battery and charging system both test good, an excessive key-off current draw is the likely cause of repeat dead batteries. Measuring parasitic draw isolates the circuit.

Question 41Battery Diagnosis and Service

What happens to battery capacity as electrolyte temperature drops well below freezing?

  1. Capacity stays constant
  2. Capacity doubles
  3. Capacity decreases Correct answer.
  4. Capacity increases

Explanation

Cold electrolyte slows the chemical reaction and raises internal resistance, so available capacity drops. This is why cold cranking amps is a distinct, lower-temperature rating.

Question 42Battery Diagnosis and Service

A technician observes that a battery's electrolyte is low in all cells. What should be added?

  1. Antifreeze
  2. Battery acid
  3. Tap water
  4. Distilled water Correct answer.

Explanation

Only water is lost through normal gassing, so distilled water is added to restore the level. Adding acid changes the electrolyte concentration and damages the battery.

Question 43Battery Diagnosis and Service

A bus is equipped with two 12-volt batteries wired in parallel. What is the result?

  1. 12 volts, double capacity Correct answer.
  2. 24 volts, same capacity
  3. 24 volts, double capacity
  4. 12 volts, half capacity

Explanation

Parallel wiring keeps voltage at 12 volts while adding the current capacities of both batteries. Series wiring would double voltage instead.

Question 44Battery Diagnosis and Service

A technician performs a voltage drop test across the battery ground cable while cranking and reads 0.6 volts. What does this indicate?

  1. Normal operation
  2. Excessive resistance in the ground circuit Correct answer.
  3. Fully charged battery
  4. Charging system fault

Explanation

A voltage drop above about 0.1 to 0.2 volts across a cable indicates excessive resistance, often from corrosion or a loose connection. The cable or connection should be cleaned or replaced.

Question 45Starting System Diagnosis and Repair

A school bus with a manual transmission will not crank, and the driver reports a single loud click from the engine compartment when the key is turned to START. Which component is the most likely cause?

  1. The ignition switch START contact
  2. The neutral safety switch circuit
  3. The starter solenoid contacts or the solenoid itself Correct answer.
  4. The battery hold-down bracket

Explanation

A single heavy click with no crank typically means the solenoid is energizing but its internal contacts are not passing current to the motor, or the solenoid plunger is not completing its stroke. A neutral safety switch or ignition switch fault usually produces no click at all. The battery hold-down bracket has no electrical function.

Question 46Starting System Diagnosis and Repair

Which voltage reading at the starter battery terminal stud indicates excessive resistance in the positive battery cable during cranking?

  1. Less than 0.5 volt
  2. Exactly battery voltage
  3. Zero volts
  4. More than 0.5 volt Correct answer.

Explanation

Voltage drop testing measures the difference between the source and the load end of a cable while current flows. A good heavy-gauge cranking cable should drop well under 0.5 volt at full cranking current; a higher reading means the cable or its connections have excessive resistance.

Question 47Starting System Diagnosis and Repair

On a bus equipped with a remote-mount starter relay, where should a technician measure to confirm the relay is receiving the crank command from the ignition switch?

  1. At the relay coil control terminal while an assistant turns the key to START Correct answer.
  2. At the battery negative post
  3. At the alternator output stud
  4. At the starter motor armature

Explanation

The control circuit is verified by measuring voltage at the relay coil terminal during the crank command. This isolates whether the fault lies in the command side or the power side of the circuit.

Question 48Starting System Diagnosis and Repair

A starter motor cranks slowly and the battery passes a load test. A voltage drop of 0.9 volt is measured across the engine ground strap during cranking. What is the correct interpretation?

  1. The battery is sulfated
  2. The starter is drawing too little current
  3. The ignition switch is misadjusted
  4. The ground strap circuit has excessive resistance and must be repaired Correct answer.

Explanation

A ground-side drop approaching 1 volt at cranking current robs the starter of voltage and reduces cranking speed. The strap and its mounting points should be cleaned and retorqued or replaced.

Question 49Starting System Diagnosis and Repair

Which condition causes a starter motor to keep cranking after the key is released from START?

  1. A grounded brush lead
  2. A worn drive pinion
  3. An open pull-in winding
  4. A welded starter solenoid contact disc Correct answer.

Explanation

If the solenoid's heavy contact disc welds closed, the motor remains connected to battery power regardless of the control circuit. The battery must be disconnected immediately to stop the cranking and prevent starter damage.

Question 50Starting System Diagnosis and Repair

A gear-reduction starter uses a planetary gear set. What is the primary purpose of the reduction gears?

  1. To increase motor speed at the pinion
  2. To eliminate the need for a solenoid
  3. To multiply motor torque delivered to the flywheel Correct answer.
  4. To reduce current draw to zero

Explanation

The reduction gears trade motor speed for torque, allowing a smaller, faster motor to produce the high torque needed to crank a large diesel engine. The pinion turns slower than the armature but with greater twisting force.