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ASE T6 Electrical/Electronic Systems (Medium/Heavy Truck) study materials
ASE T6 Electrical/Electronic Systems (Medium/Heavy Truck) study resources

ASE T6 Electrical/Electronic Systems (Medium/Heavy Truck) practice questions

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Question 1General Electrical/Electronic System Diagnosis

A technician is testing a circuit with a digital multimeter set to measure voltage. To measure the voltage drop across a component, how should the meter be connected?

  1. Across the battery terminals only, with the component disconnected
  2. In series with the component, breaking the circuit
  3. In parallel with the component, with the meter's positive lead on the more positive side Correct answer.
  4. In series with the load while the circuit is energized

Explanation

A voltmeter has very high internal resistance and must be connected in parallel across the component so it senses the potential difference without drawing significant current. Breaking the circuit to insert the meter is the method for measuring current, not voltage.

Question 2General Electrical/Electronic System Diagnosis

Which meter setting should be used to check a suspected open in a wire when the circuit is de-energized?

  1. AC volts
  2. DC volts
  3. Resistance (ohms) Correct answer.
  4. Frequency

Explanation

Resistance measurement is performed on a de-energized circuit and reveals whether a path exists through the wire. An open conductor shows very high or infinite resistance. Voltage and frequency settings require an energized circuit to give meaningful readings.

Question 3General Electrical/Electronic System Diagnosis

A technician measures 0.0 volts between the negative battery post and the engine block while cranking, and the starter cranks slowly. What does this reading indicate?

  1. The alternator is overcharging
  2. The ground path between the block and battery is good Correct answer.
  3. The battery is fully discharged
  4. The starter solenoid is open

Explanation

A voltage drop test measures the loss across a connection while current flows. A reading near zero across the engine-to-battery ground path means the connection is clean and offering little resistance. Excessive drop (typically over about 0.2 to 0.5 volt depending on the circuit) would indicate a poor connection.

Question 4General Electrical/Electronic System Diagnosis

A truck's battery is being tested and reads 12.6 volts at rest. What does this indicate about the battery's state of charge?

  1. Deeply discharged
  2. About 50 percent charged
  3. Defective and requiring replacement
  4. Fully charged Correct answer.

Explanation

A healthy lead-acid battery at rest and at room temperature reads approximately 12.6 volts when fully charged. Roughly 12.2 volts corresponds to about 50 percent state of charge. Voltage alone cannot confirm a battery is defective; a load or conductance test is required.

Question 5General Electrical/Electronic System Diagnosis

During a charging system check, a technician measures 14.2 volts at the battery with the engine running at fast idle and all accessories off. What is the best interpretation?

  1. The alternator diode trio is shorted
  2. The charging system output is within normal range Correct answer.
  3. The voltage regulator is stuck open
  4. The battery cables have excessive resistance

Explanation

Normal charging voltage for a 12-volt system typically falls in the range of about 13.5 to 14.5 volts at the battery. A reading of 14.2 volts indicates the alternator is producing adequate output. Diode or regulator faults usually produce low, erratic, or excessive voltage readings.

Question 6General Electrical/Electronic System Diagnosis

A parasitic draw test shows a current of 0.45 amp after all modules have gone to sleep. What is the most appropriate next step?

  1. Measure voltage drop across fuses to locate the offending circuit Correct answer.
  2. Replace the battery
  3. Disconnect the alternator and stop testing
  4. Increase alternator output

Explanation

A parasitic draw above the manufacturer's specification (commonly around 0.05 amp or less after sleep) indicates a circuit staying awake. Measuring millivolt drop across fuses lets the technician identify which circuit is drawing current without disconnecting each one. Replacing the battery does not correct the underlying draw.

Question 7General Electrical/Electronic System Diagnosis

A technician is checking a relay-controlled circuit. With the relay energized, voltage is present at the relay output terminal but not at the load. What is the most likely cause?

  1. Open relay coil
  2. Open circuit between the relay and the load Correct answer.
  3. Faulty ground at the load
  4. Shorted relay contacts

Explanation

If voltage reaches the relay output but does not reach the load, the conductor or connector between those points is open. The relay coil and contacts are functioning because the relay energized and passed voltage to its output terminal. A load ground fault would not prevent voltage from arriving at the load.

Question 8General Electrical/Electronic System Diagnosis

What is the primary purpose of a twisted pair of wires in a truck's data communication network?

  1. To allow higher voltage operation
  2. To provide a redundant ground path
  3. To reduce electromagnetic interference Correct answer.
  4. To increase current-carrying capacity

Explanation

Twisting the two signal conductors causes induced noise to cancel, which reduces electromagnetic interference on the data bus. This is a signal-integrity measure, not a means of increasing current capacity or voltage. The pair carries differential signals, not power or ground.

Question 9General Electrical/Electronic System Diagnosis

A J1939 data bus is being diagnosed. A technician measures about 60 ohms across the CAN high and CAN low terminals with the bus powered down. What does this indicate?

  1. Both terminating resistors are present and the bus is intact Correct answer.
  2. The bus is shorted to ground
  3. One terminating resistor is open
  4. A module is holding the bus dominant

Explanation

A J1939 bus has two 120-ohm terminating resistors in parallel, which produces about 60 ohms when measured across the bus with power removed. A reading near 120 ohms suggests one terminator is missing or open. A short or stuck-dominant condition would show a much different resistance or voltage reading.

Question 10General Electrical/Electronic System Diagnosis

A technician finds a blown fuse protecting a circuit. What is the most appropriate first action?

  1. Install a fuse with a higher current rating
  2. Replace the fuse and recheck the circuit
  3. Locate and repair the cause of the overcurrent Correct answer.
  4. Bypass the fuse with a jumper wire

Explanation

A fuse opens because current exceeded its rating, usually from a short or overload. The correct approach is to find and correct the fault before restoring power. Installing a larger fuse or bypassing the fuse removes protection and can damage wiring or components.

Question 11General Electrical/Electronic System Diagnosis

A headlamp circuit has excessive voltage drop on the ground side. Which symptom is most likely?

  1. The lamp flashes rapidly
  2. The lamp is dimmer than normal Correct answer.
  3. The lamp is brighter than normal
  4. The lamp stays on with the switch off

Explanation

Excess resistance in the ground return reduces the voltage actually available across the lamp filament, so the lamp glows dimly. A brighter lamp would suggest excessive voltage. Rapid flashing points to a turn-signal or flasher issue, and staying on with the switch off points to a short to power.

Question 12General Electrical/Electronic System Diagnosis

A technician is using a scan tool and sees a code indicating a sensor signal is out of range high. Which condition could cause this?

  1. A disconnected battery negative cable
  2. An open signal return wire
  3. A shorted sensor ground
  4. A signal wire shorted to a voltage source Correct answer.

Explanation

A signal circuit shorted to voltage pulls the sensor signal above its normal range, which the module reports as out of range high. An open return or a disconnected ground would typically drive the signal low or cause a reference fault. The module compares the signal voltage against expected limits.

Question 13General Electrical/Electronic System Diagnosis

Which tool is best suited for detecting an intermittent wiring fault while the vehicle is being driven over rough roads?

  1. A non-contact thermometer
  2. A digital storage oscilloscope with min/max capture Correct answer.
  3. A compression gauge
  4. A test light

Explanation

An oscilloscope with min/max or glitch capture records brief signal interruptions that a simple meter or test light would miss. Intermittent faults often appear as momentary dropouts during vibration. A test light, thermometer, and compression gauge do not capture fast electrical transients.

Question 14General Electrical/Electronic System Diagnosis

A technician is testing a PWM-controlled solenoid circuit. The solenoid is weak, and the driver module is suspected. Which measurement best confirms the module is controlling the solenoid?

  1. Battery voltage at rest
  2. Resistance of the solenoid coil only
  3. Current draw of the alternator
  4. Duty cycle of the control signal at the solenoid Correct answer.

Explanation

A pulse-width-modulated output is verified by measuring its duty cycle, which shows how long the driver is commanding the solenoid on. Coil resistance only checks the solenoid itself, not the module's control. Alternator current and resting battery voltage are unrelated to the PWM command.

Question 15General Electrical/Electronic System Diagnosis

What does a reading of infinite resistance across a normally closed switch indicate?

  1. The meter is set incorrectly for this test
  2. The switch is operating normally
  3. The switch contacts are open or the switch is defective Correct answer.
  4. The switch contacts are closed and conducting

Explanation

Infinite resistance means no continuity through the switch. A normally closed switch should read near zero ohms when closed, so infinite resistance indicates the contacts are open or the switch has failed. Verifying meter function and lead placement is good practice but the reading itself points to an open.

Question 16General Electrical/Electronic System Diagnosis

A technician measures battery voltage at 12.4 volts with the key off, then 11.8 volts when the ignition is turned on. What does this change most likely indicate?

  1. The alternator is overcharging
  2. The ground strap is disconnected
  3. The battery has failed internally
  4. A normal load-related voltage drop from accessories Correct answer.

Explanation

Turning the key on energizes accessories and modules, which draws current and lowers the battery's terminal voltage slightly. A drop of about half a volt is normal. A failed battery would typically show poor performance under load testing, and a disconnected ground strap would prevent operation entirely.

Question 17General Electrical/Electronic System Diagnosis

A technician is diagnosing a circuit protected by a self-resetting circuit breaker that keeps tripping. What is the most likely cause?

  1. A worn ignition switch
  2. A short or overload in the protected circuit Correct answer.
  3. A discharged battery
  4. A loose ground at the module

Explanation

A self-resetting breaker trips when current exceeds its rating and resets when it cools, so repeated tripping points to a persistent short or overload in the protected circuit. A discharged battery or loose ground does not normally cause overcurrent. The breaker is responding to a real fault that must be located.

Question 18General Electrical/Electronic System Diagnosis

When performing a voltage drop test on a starter circuit, the technician should measure across which points during cranking?

  1. From the battery positive post to the battery negative post
  2. From the battery positive post to the starter terminal Correct answer.
  3. From the alternator output to ground
  4. From the starter case to the frame

Explanation

A voltage drop test on the positive starter feed places the meter across the cable and connections between the battery positive post and the starter terminal while current flows. This reveals resistance in the feed path. Measuring across the battery posts shows total system voltage, not the drop in the cable.

Question 19General Electrical/Electronic System Diagnosis

A technician observes that a truck's dash warning lamps all illuminate when the ignition is turned on but do not go out after the engine starts. Which area should be investigated first?

  1. The brake lining thickness
  2. The transmission shift points
  3. The fuel injection timing
  4. The charging system output and module communications Correct answer.

Explanation

Warning lamps that stay on after start often indicate low charging voltage or a module that is not communicating correctly. The lamps are controlled by the instrument cluster based on inputs from the charging system and other modules. Mechanical systems such as injection timing, shift points, and brake linings do not directly control lamp operation.

Question 20General Electrical/Electronic System Diagnosis

Which condition would cause a relay coil to fail to energize even though the control switch is closed and voltage is present at the coil's power terminal?

  1. A blown fuse in the load circuit
  2. A broken load ground
  3. A shorted load device
  4. An open in the coil's ground-side control wire Correct answer.

Explanation

A relay coil needs both power and a complete ground path through its control circuit to energize. If power is present but the ground-side control wire is open, no current flows through the coil. Faults in the load circuit do not prevent the coil from energizing.

Question 21General Electrical/Electronic System Diagnosis

What is the purpose of a dedicated chassis ground strap between the engine and the frame?

  1. To limit charging system output
  2. To supply positive voltage to the starter
  3. To carry return current and provide a low-resistance ground path Correct answer.
  4. To shield the data bus from interference

Explanation

Ground straps provide a low-resistance return path for current between major components such as the engine, frame, and cab. Poor bonding causes voltage drops and erratic operation of modules and accessories. Ground straps do not carry positive voltage, shield data, or regulate charging output.

Question 22General Electrical/Electronic System Diagnosis

A technician is checking a sensor's 5-volt reference and measures 4.2 volts with the sensor disconnected. What is the most likely explanation?

  1. The battery is overcharged
  2. The sensor is shorted internally
  3. The sensor signal wire is open
  4. The reference circuit has excessive resistance or a partial short Correct answer.

Explanation

A 5-volt reference that reads low with the sensor disconnected points to resistance in the reference feed or a partial short pulling the voltage down. The module regulates the reference, so a low reading at the connector indicates a circuit problem. An internally shorted sensor or an open signal wire would not cause a low reference with the sensor removed.

Question 23General Electrical/Electronic System Diagnosis

A technician needs to verify that a module is receiving both battery power and ignition power at its connector. Which test confirms this?

  1. Measure resistance from the module case to ground
  2. Check the module's mounting bolt torque
  3. Measure AC ripple at the battery
  4. Measure voltage at each power terminal with the appropriate key state Correct answer.

Explanation

Modules typically have separate battery (constant) and ignition (switched) power feeds. Verifying each requires measuring voltage at the correct terminal with the key in the proper position. Resistance to ground checks the ground path, and ripple or bolt torque do not confirm power feeds.

Question 24General Electrical/Electronic System Diagnosis

A technician is diagnosing a slow-cranking complaint. Battery voltage is good, and voltage drop on both the positive feed and the ground path is within specification. What should be checked next?

  1. Alternator diode pattern
  2. Headlamp circuit voltage drop
  3. Data bus termination resistance
  4. Starter current draw and mechanical resistance in the engine Correct answer.

Explanation

With supply and ground paths verified, the remaining suspects are the starter itself and mechanical drag in the engine. Measuring starter current draw and checking for excessive rotational resistance isolates the cause. Charging, data bus, and lighting circuits do not explain slow cranking.

Question 25General Electrical/Electronic System Diagnosis

Which practice best protects a vehicle's electronic modules when performing electrical diagnostic work?

  1. Use a test light to probe module terminals
  2. Connect a charger to the battery at high current during testing
  3. Leave the ignition on during all tests
  4. Disconnect the battery negative cable before disconnecting major connectors Correct answer.

Explanation

Disconnecting the battery negative cable first removes power and reduces the risk of arcing or voltage spikes that can damage modules. Probing module terminals with a test light or applying high charging current can introduce damaging transients. Leaving the ignition on during connector work also risks faults.

Question 26General Electrical/Electronic System Diagnosis

A technician is testing a circuit and finds that the resistance between two points is 0.2 ohm when it should be near 0 ohm. Which interpretation is correct?

  1. The circuit is shorted to ground.
  2. The circuit has excessive resistance and may cause a voltage drop. Correct answer.
  3. The circuit is open and current cannot flow.
  4. The circuit is functioning normally because some resistance is always present.

Explanation

Resistance in a circuit causes a voltage drop proportional to current flow. A reading of 0.2 ohm in a circuit that should have near-zero resistance indicates excessive resistance, which can reduce current and cause malfunction. An open circuit would show infinite resistance, and a short to ground would typically show very low resistance to ground, not necessarily between the two points being tested.

Question 27General Electrical/Electronic System Diagnosis

Which instrument is used to measure the current flowing through a circuit without disconnecting the circuit?

  1. An ohmmeter
  2. A clamp-on ammeter Correct answer.
  3. A test light
  4. A voltmeter

Explanation

A clamp-on ammeter measures current by sensing the magnetic field around a conductor, so it can be clamped around a wire without breaking the circuit. A voltmeter measures voltage, an ohmmeter measures resistance (and requires the circuit to be de-energized), and a test light only indicates the presence of voltage.

Question 28General Electrical/Electronic System Diagnosis

When testing a diode with a digital multimeter in diode-test mode, a good diode should show which reading?

  1. Approximately 0.6 to 0.7 volt in one direction and OL in the other. Correct answer.
  2. Approximately 0.6 to 0.7 volt in both directions.
  3. OL in both directions.
  4. Approximately 0 volt in both directions.

Explanation

A good diode allows current to flow in one direction (forward bias) with a small voltage drop, typically 0.6 to 0.7 volt for a silicon diode, and blocks current in the reverse direction, showing OL (over limit). A reading of 0.6 to 0.7 volt in both directions indicates a shorted diode, while OL in both directions indicates an open diode.

Question 29General Electrical/Electronic System Diagnosis

A technician is performing a voltage drop test on a ground circuit. The meter should be connected:

  1. Between the positive battery post and the component ground.
  2. Between the component power wire and the component ground.
  3. Between the positive battery post and the battery negative post.
  4. Between the component ground and the battery negative post. Correct answer.

Explanation

A voltage drop test on a ground circuit measures the voltage difference between the component ground point and the battery negative post while current is flowing. This reveals any unwanted resistance in the ground path. Connecting across the battery posts measures battery voltage, not voltage drop.

Question 30General Electrical/Electronic System Diagnosis

A technician is diagnosing a circuit that intermittently loses power. Which test is most effective for locating the fault?

  1. A visual inspection of the wiring harness.
  2. A resistance test of the circuit with the component disconnected.
  3. A voltage drop test while the circuit is under load and the fault is present. Correct answer.
  4. A continuity test of the circuit with the power removed.

Explanation

Intermittent faults often occur only under load or when the vehicle is moving. A voltage drop test performed while the circuit is energized and the fault is occurring can reveal excessive resistance that a static resistance or continuity test might miss. Visual inspection may not reveal internal wire damage.

Question 31General Electrical/Electronic System Diagnosis

A technician is testing a Hall-effect sensor. Which condition would cause the sensor signal to remain at a fixed voltage regardless of the target wheel position?

  1. A shorted sensor signal wire to ground Correct answer.
  2. A missing sensor power supply
  3. An open sensor ground circuit
  4. A broken target wheel tooth

Explanation

A Hall-effect sensor produces a digital square wave signal as the target wheel rotates. If the signal wire is shorted to ground, the signal will be pulled low and remain at a fixed voltage. A missing power supply or open ground would prevent the sensor from operating at all, typically resulting in no signal.

Question 32General Electrical/Electronic System Diagnosis

A technician is using a scan tool to check for fault codes. The tool displays a code for a sensor circuit high voltage. Which condition is most likely?

  1. The sensor ground circuit is open.
  2. The sensor is unplugged.
  3. The sensor signal wire is shorted to ground.
  4. The sensor signal wire is open. Correct answer.

Explanation

A high voltage code on a sensor circuit typically indicates that the signal wire is open or shorted to voltage, causing the module to see a higher than normal voltage. An open signal wire can cause the module's pull-up resistor to pull the signal voltage high. A short to ground would cause a low voltage code.

Question 33General Electrical/Electronic System Diagnosis

Which of the following is the correct way to test a relay's coil circuit?

  1. Measure voltage at the coil terminals with the relay energized.
  2. Measure voltage at the relay output terminal with the relay energized.
  3. Measure continuity between the normally open and normally closed contacts.
  4. Measure resistance between the coil terminals and compare to specification. Correct answer.

Explanation

The relay coil is a winding of wire and should have a specific resistance. Measuring resistance across the coil terminals and comparing to the manufacturer's specification verifies the coil's integrity. Measuring voltage at the output or contacts tests the relay's switching function, not the coil circuit itself.

Question 34General Electrical/Electronic System Diagnosis

A technician is diagnosing a vehicle with multiple module communication faults. The technician should first check:

  1. The module part numbers.
  2. The data bus resistance.
  3. The scan tool software version.
  4. The battery voltage and ground connections. Correct answer.

Explanation

Multiple communication faults often stem from a common power or ground issue. Checking battery voltage and ground connections ensures that all modules have a solid electrical foundation before delving into data bus diagnostics. Low voltage or poor grounds can cause erratic module operation and communication errors.

Question 35General Electrical/Electronic System Diagnosis

A technician is testing a PWM-controlled solenoid. The solenoid is weak, and the driver module is suspected. Which test is most appropriate?

  1. Measure the resistance of the solenoid coil.
  2. Measure the voltage at the solenoid with a voltmeter.
  3. Use an oscilloscope to view the duty cycle and voltage pattern at the solenoid. Correct answer.
  4. Check for continuity between the solenoid and ground.

Explanation

A PWM-controlled solenoid is driven by a pulsed signal, so a standard voltmeter may average the voltage and not reveal the true waveform. An oscilloscope can display the duty cycle, frequency, and voltage peaks, allowing the technician to verify the driver module's output and the solenoid's response. Resistance and continuity tests do not assess the dynamic control signal.

Question 36General Electrical/Electronic System Diagnosis

A technician is using a multimeter to check for a short to voltage in a circuit. The technician should:

  1. Measure current flow through the circuit with the component connected.
  2. Measure voltage on the circuit with the component disconnected and the power on. Correct answer.
  3. Measure resistance between the circuit and ground with the power on.
  4. Measure resistance between the circuit and ground with the power off.

Explanation

To check for a short to voltage, the circuit should be isolated from its normal power source and the component disconnected. Then, with the ignition on, measure voltage on the circuit. If voltage is present, there is a short to another voltage source. Resistance tests are done with power off.

Question 37General Electrical/Electronic System Diagnosis

A technician is diagnosing a circuit with a self-resetting circuit breaker that trips repeatedly. Which is the most likely cause?

  1. A faulty circuit breaker.
  2. High resistance in the circuit.
  3. A short to ground in the circuit. Correct answer.
  4. An open circuit in the load.

Explanation

A self-resetting circuit breaker trips when current exceeds its rating. A short to ground causes excessive current flow, repeatedly tripping the breaker. An open circuit would cause no current flow, and high resistance would reduce current, not increase it.

Question 38General Electrical/Electronic System Diagnosis

A technician is testing a potentiometer-type sensor. The signal voltage should:

  1. Remain constant regardless of sensor position.
  2. Jump abruptly at certain positions.
  3. Change smoothly as the sensor is moved through its range. Correct answer.
  4. Be zero volts at all positions.

Explanation

A potentiometer sensor varies resistance as its wiper moves, producing a smooth change in signal voltage. An erratic or jumpy signal indicates a worn or dirty potentiometer. A constant voltage would indicate a faulty sensor or circuit.

Question 39General Electrical/Electronic System Diagnosis

A technician is using a lab scope to diagnose a CAN bus. The technician observes that the CAN high and CAN low signals are both at about 2.5 volts and do not change. What is the most likely cause?

  1. The bus is shorted to battery voltage.
  2. The bus is shorted to ground.
  3. The bus is shorted together. Correct answer.
  4. The bus is open.

Explanation

CAN high and CAN low are differential signals that normally swing between approximately 2.5 and 3.5 volts (high) and 2.5 and 1.5 volts (low). If both lines are at 2.5 volts and not changing, it suggests the two lines are shorted together, preventing differential signaling. A short to ground or battery would pull both lines to those respective voltages.

Question 40General Electrical/Electronic System Diagnosis

A technician is diagnosing a vehicle with a parasitic draw. After connecting an ammeter in series with the battery, the technician should:

  1. Turn on all accessories to see if the draw increases.
  2. Wait for all modules to go to sleep and then measure the current. Correct answer.
  3. Measure voltage across the battery while cranking.
  4. Disconnect the ammeter and check for codes.

Explanation

To accurately measure parasitic draw, the technician must wait for all modules to enter sleep mode, which can take several minutes. Then the current draw should be compared to the manufacturer's specification. Turning on accessories would increase current and not test for parasitic draw.

Question 41Battery and Starting System Diagnosis and Repair

A fully charged 12-volt lead-acid battery at 77°F (25°C) should show approximately what open-circuit voltage?

  1. 10.5 volts
  2. 12.6 volts Correct answer.
  3. 12.0 volts
  4. 13.8 volts

Explanation

A healthy, fully charged 12-volt battery rests near 12.6 volts at room temperature. Each of the six cells produces about 2.1 volts at full charge. Readings are corrected for temperature, dropping as the battery gets colder.

Question 42Battery and Starting System Diagnosis and Repair

A technician performs a battery load test. The tester should be applied for what duration to obtain a valid result?

  1. About 5 seconds
  2. About 3 minutes
  3. About 60 seconds
  4. About 15 seconds Correct answer.

Explanation

A carbon-pile or conductance load test holds the load for about 15 seconds so the battery voltage stabilizes under load. The reading is taken at the end of that interval. Shorter or much longer applications give misleading results.

Question 43Battery and Starting System Diagnosis and Repair

Which test best identifies a battery with a bad cell that still shows acceptable open-circuit voltage?

  1. Alternator output test
  2. Voltage drop across the ground strap
  3. Hydrometer reading of each cell Correct answer.
  4. Starter draw test

Explanation

A hydrometer compares specific gravity cell to cell. One cell reading noticeably lower than the others indicates a failed cell. Open-circuit voltage can look normal because the good cells mask the weak one.

Question 44Battery and Starting System Diagnosis and Repair

A battery that passes a conductance test but fails to crank a warm engine most likely indicates what?

  1. The conductance tester is always wrong
  2. An overcharged battery
  3. A shorted ignition switch
  4. A poor connection or excessive circuit resistance Correct answer.

Explanation

Conductance testers evaluate the battery's internal condition, not the cables and connections. If the battery tests good but cranking is weak, inspect terminal condition and circuit resistance. A voltage drop test across cables will locate the problem.

Question 45Battery and Starting System Diagnosis and Repair

During a starter draw test, cranking current is measured at 600 amps on an engine rated for 200 amps. What is the most likely cause?

  1. A seized or dragging starter or engine Correct answer.
  2. A fully charged battery
  3. High alternator output
  4. An open field winding

Explanation

Excessive cranking current means the starter is working against abnormally high mechanical resistance. A dragging starter, binding engine, or locked accessory can cause this. Normal cranking current is specified by the manufacturer.

Question 46Battery and Starting System Diagnosis and Repair

A voltage drop test is being performed on the positive battery cable to the starter. The maximum acceptable drop during cranking is generally:

  1. 0.5 volt or less Correct answer.
  2. 2.0 volts or less
  3. 5.0 volts or less
  4. 10.0 volts or less

Explanation

Voltage drop across a good high-current cable should be about 0.5 volt or less during cranking. Higher drop indicates excessive resistance from corrosion or loose connections. This test locates resistance the ohmmeter may miss under load.

Question 47Battery and Starting System Diagnosis and Repair

A starter solenoid clicks repeatedly but the engine does not crank, and battery voltage stays steady at 12.4 volts during the clicks. What should be checked first?

  1. The alternator belt tension
  2. Control circuit voltage at the solenoid terminal Correct answer.
  3. The battery's specific gravity
  4. The engine coolant temperature sensor

Explanation

Repeated clicking with steady battery voltage suggests the solenoid is not getting enough current to hold the plunger in. Check control-circuit voltage at the solenoid S terminal. Low voltage there points to the ignition switch, neutral switch, or wiring.

Question 48Battery and Starting System Diagnosis and Repair

What is the primary purpose of the neutral safety switch in the starting circuit?

  1. To disconnect the alternator during cranking
  2. To limit starter current draw
  3. To increase cranking speed
  4. To prevent cranking unless the transmission is in park or neutral Correct answer.

Explanation

The neutral safety switch opens the starter control circuit unless the transmission is in park or neutral. This prevents the vehicle from lurching when the key is turned. It is wired in series with the solenoid control circuit.

Question 49Battery and Starting System Diagnosis and Repair

A vehicle cranks slowly and the battery is known good. A voltage drop of 0.9 volt is measured from the battery negative post to the engine block during cranking. What does this indicate?

  1. Normal operation
  2. Excessive resistance in the ground circuit Correct answer.
  3. A faulty starter solenoid
  4. A weak alternator

Explanation

Ground-side voltage drop above roughly 0.2 to 0.3 volt during cranking indicates excessive resistance. The engine block ground strap or connection is likely corroded or loose. Cleaning or replacing the ground cable restores cranking performance.

Question 50Battery and Starting System Diagnosis and Repair

Which condition is most likely to cause a battery to boil and lose electrolyte?

  1. A loose battery hold-down
  2. Low ambient temperature
  3. A sulfated positive plate
  4. Overcharging from a faulty voltage regulator Correct answer.

Explanation

Overcharging drives excessive current into the battery and causes gassing, which boils off electrolyte. A faulty voltage regulator or excessive charging voltage is the usual cause. Charging voltage should be regulated near 13.8 to 14.5 volts.