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ASE XEV2 practice questions

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Question 1High-Voltage System Safety Practices and Personal Protective Equipment

Which class of rubber insulating glove carries a maximum use voltage of 1,000 volts AC?

  1. Class 0 Correct answer.
  2. Class 4
  3. Class 00
  4. Class 2

Explanation

Rubber insulating gloves are assigned ASTM class designations tied to a maximum use voltage. Class 00 is limited to 500 V AC, Class 0 to 1,000 V AC, and the higher classes extend upward from there. Glove class must always meet or exceed the voltage of the circuit being worked.

Question 2High-Voltage System Safety Practices and Personal Protective Equipment

How often must in-service rubber insulating gloves be given a periodic electrical retest?

  1. Every 12 months
  2. Every 3 months
  3. Only when they are first purchased
  4. Every 6 months Correct answer.

Explanation

Electrical testing requirements for insulating gloves call for a test before first issue and at fixed intervals thereafter. For rubber insulating gloves that interval is six months. Gloves must also be retested after any repair.

Question 3High-Voltage System Safety Practices and Personal Protective Equipment

Leather protectors worn over rubber insulating gloves are worn mainly to:

  1. Increase the dielectric strength of the rubber glove
  2. Protect the rubber glove from physical damage Correct answer.
  3. Keep the technician's hands warm in cold weather
  4. Allow the glove to be used above its voltage rating

Explanation

Leather protectors provide mechanical protection only; they add nothing to the electrical insulation. Their job is to keep the rubber glove from being cut, snagged, or abraded during work. The rubber glove underneath still provides the dielectric barrier.

Question 4High-Voltage System Safety Practices and Personal Protective Equipment

How is the high-voltage service disconnect on a battery pack best described?

  1. A fuse that opens permanently on overload
  2. A low-voltage switch that disables the 12 V system
  3. A removable plug that opens the HV circuit at the pack Correct answer.
  4. An automatic breaker that resets after a fault

Explanation

The service disconnect is a manually removable device that interrupts the high-voltage circuit, usually by breaking the series connection between modules. It is part of the isolation procedure, not an overload protection device. Removing it does not by itself guarantee the pack is de-energized.

Question 5High-Voltage System Safety Practices and Personal Protective Equipment

Insulated hand tools intended for high-voltage work are normally marked with:

  1. An arc flash category number
  2. A temperature rating only
  3. A 1,000 V rating and the maker's mark Correct answer.
  4. A torque specification only

Explanation

Insulated tools built to the recognized standard are marked by the manufacturer with the voltage they are rated for, commonly 1,000 V AC, along with the maker's identification. Tools without such markings should not be treated as insulated. Ratings apply only while the insulation is undamaged.

Question 6High-Voltage System Safety Practices and Personal Protective Equipment

Before beginning work on an energized high-voltage system, the technician should remove:

  1. The 12 V battery and the key fob
  2. Safety glasses and the arc-rated face shield
  3. Rings, watches, and other metal jewelry Correct answer.
  4. The leather protectors worn over the rubber gloves

Explanation

Conductive jewelry can bridge a terminal to ground or create a low-resistance path through the body, causing severe burns. All metal jewelry should be removed before any high-voltage work begins. PPE such as glasses, shields, and protectors stay on.

Question 7High-Voltage System Safety Practices and Personal Protective Equipment

High-voltage cables on most electrified vehicles are identified by:

  1. A green grounding braid
  2. Orange cable jacket or orange conduit Correct answer.
  3. Black insulation marked with white stripes
  4. Red insulation on all HV cables

Explanation

Orange is the industry convention for identifying high-voltage conductors and their conduit so they are not mistaken for 12 V wiring. Technicians should treat any orange cable as energized until isolation is completed and verified. Color coding is a warning aid, not proof of state.

Question 8High-Voltage System Safety Practices and Personal Protective Equipment

A coworker is being shocked and cannot release an energized high-voltage conductor. Your first action should be to:

  1. Hand the coworker an insulated tool so they can break contact
  2. Spray the area with a CO2 extinguisher
  3. Pull the coworker away by the arm
  4. De-energize the circuit at the power source Correct answer.

Explanation

Rescuers are frequently injured because they touch a victim who is still in contact with an energized source. The circuit must be de-energized before the victim is touched. Only then should first aid and emergency notification proceed.

Question 9High-Voltage System Safety Practices and Personal Protective Equipment

A technician rolls the cuff of a Class 0 rubber glove to trap air inside. This pre-use test is performed to:

  1. Confirm the glove's class matches the meter's CAT rating
  2. Measure the glove's insulation resistance in megohms
  3. Check the glove for pinholes, punctures, and cuts Correct answer.
  4. Verify the leather protector fits over the glove

Explanation

Trapping air and watching for a ballooning or deflating area reveals small holes and thin spots that visual inspection alone can miss. The test supplements, but does not replace, the periodic electrical retest. Any glove that fails the air test is removed from service.

Question 10High-Voltage System Safety Practices and Personal Protective Equipment

How should rubber insulating gloves be stored between uses?

  1. On a shelf directly above a battery charging station
  2. In a cool, dry place away from sunlight and ozone Correct answer.
  3. Inside the vehicle's HV battery compartment
  4. Folded tightly in a toolbox to save space

Explanation

Rubber compounds degrade when exposed to heat, sunlight, ozone, oils, and sharp folds. Gloves should be kept flat or in a issued bag in a cool, dry location. Storage near charging equipment exposes them to ozone generated by arcing contacts.

Question 11High-Voltage System Safety Practices and Personal Protective Equipment

A technician will measure voltage on a 400 V DC high-voltage bus. Which meter and probe combination is appropriate?

  1. Any meter with a 10 A current range
  2. CAT III, 1,000 V DC with matching probes Correct answer.
  3. CAT I, 300 V
  4. CAT II, 600 V AC only

Explanation

Meters and probes must be rated for the circuit voltage and for the transient environment in which they are used. For automotive high-voltage work a CAT III rating at or above the system voltage is appropriate. The probes must carry the same rating as the meter.

Question 12High-Voltage System Safety Practices and Personal Protective Equipment

After the high-voltage service disconnect is removed, the technician must wait the OEM-specified time before opening the pack because:

  1. The battery modules must cool to ambient temperature
  2. The BMS must finish logging the disconnect event
  3. The 12 V battery must be recharged by the converter
  4. Capacitors and inverters may hold a dangerous charge Correct answer.

Explanation

Capacitors in inverters and other HV components can retain a lethal charge after the pack is isolated. The specified wait allows bleed-down circuits to discharge them. Voltage must still be verified before contact is made.

Question 13High-Voltage System Safety Practices and Personal Protective Equipment

Before touching high-voltage conductors that have been isolated, the technician should:

  1. Check that the HV warning lamp on the dash is out
  2. Verify zero volts with a meter checked on a known source Correct answer.
  3. Confirm the service disconnect is removed, then proceed with the work
  4. Touch the conductor briefly with the back of the hand

Explanation

Isolation is only proven by an actual voltage measurement at the point of work. The meter itself must be proven on a known live source before and after the test so a failed meter cannot give a false zero reading. Indicator lamps and disconnect removal are not proof of a de-energized circuit.

Question 14High-Voltage System Safety Practices and Personal Protective Equipment

The arc flash boundary is the distance at which:

  1. The HV system's audible warning can be heard
  2. The vehicle must be shifted into park
  3. An unprotected person could receive a second-degree burn Correct answer.
  4. The high-voltage battery will begin to thermally run away

Explanation

The arc flash boundary is defined by the incident energy level that causes a second-degree burn to unprotected skin. Inside that boundary, arc-rated PPE is required. The boundary is determined by available energy and working distance, not by battery chemistry.

Question 15High-Voltage System Safety Practices and Personal Protective Equipment

When an arc-rated face shield is worn for high-voltage work, the technician should also wear:

  1. Nothing else, because the shield covers the face
  2. Leather gloves only
  3. Safety glasses underneath the shield Correct answer.
  4. A hard hat only

Explanation

Face shields protect against arc blast and molten debris but leave the eyes exposed from below and the sides. Safety glasses worn underneath provide primary eye protection. Both are required, and neither substitutes for the other.

Question 16High-Voltage System Safety Practices and Personal Protective Equipment

Lockout/tagout on an electrified vehicle typically requires:

  1. A note taped to the steering wheel
  2. A lock and tag on the energy-isolating device Correct answer.
  3. Removing the key fob from the vehicle
  4. Disconnecting only the 12 V auxiliary battery

Explanation

Lockout/tagout physically secures the energy-isolating device so it cannot be re-energized while work is in progress. The lock is applied and the key retained by the technician performing the work. A tag alone communicates intent but provides no physical protection.

Question 17High-Voltage System Safety Practices and Personal Protective Equipment

How should a removed high-voltage battery pack be handled while it awaits repair?

  1. Stacked on top of other packs to save floor space
  2. Standing on end in a walkway so it is visible
  3. On a steel workbench next to the welder
  4. On a non-conductive surface, terminals covered Correct answer.

Explanation

A removed pack should sit in a designated area on a non-conductive surface with its terminals protected against accidental contact. Keeping it away from conductive benches, welding, and traffic limits arcing and impact hazards. Packs should never be stacked or left in walkways.

Question 18High-Voltage System Safety Practices and Personal Protective Equipment

The one-hand rule is used during high-voltage measurements to:

  1. Confirm that only one HV circuit is being tested
  2. Allow the probe to be held with both hands
  3. Minimize the path for current through the chest Correct answer.
  4. Keep the meter steady while reading the display

Explanation

Current passing hand-to-hand crosses the heart and is far more likely to be fatal. Working with one hand kept clear reduces the chance of a through-chest path if contact occurs. The technique is a body-positioning safeguard, not a measurement method.

Question 19High-Voltage System Safety Practices and Personal Protective Equipment

Rubber insulating gloves that fail a pre-use inspection should be:

  1. Marked OK and used only for low-voltage work
  2. Kept in the toolbox as spare gloves
  3. Repaired with a patch kit by the technician
  4. Removed from service, defaced, and replaced Correct answer.

Explanation

Defective insulating gloves cannot be restored to service by field repair and must never serve as backups. The glove is destroyed or clearly marked so no one else can use it. A replacement of the correct class is then issued.

Question 20High-Voltage System Safety Practices and Personal Protective Equipment

If a high-voltage battery begins to vent or smoke in the shop, the technician should:

  1. Spray the pack with CO2 from close range
  2. Open the pack case to find the source
  3. Continue working while wearing a respirator
  4. Evacuate and call emergency responders Correct answer.

Explanation

Venting or smoking indicates a possible thermal runaway, which can escalate rapidly and release toxic and flammable gases. The area should be cleared and the emergency plan activated. Opening the case or approaching closely exposes the technician to arc, fire, and gas hazards.

Question 21High-Voltage System Safety Practices and Personal Protective Equipment

Arc flash incident energy at a given working distance is determined primarily by:

  1. The state of charge of the 12 V battery
  2. The available fault current and the time the arc is sustained Correct answer.
  3. The voltage class of the rubber insulating gloves being worn
  4. The color coding of the high-voltage cables

Explanation

Incident energy rises with the magnitude of available fault current and with how long the arc persists before the circuit is cleared. Working distance is the other key variable. PPE selection follows from that calculated energy, not from the technician's glove class.

Question 22High-Voltage System Safety Practices and Personal Protective Equipment

An insulation monitoring device on an electrified vehicle continuously evaluates:

  1. The resistance between the HV system and chassis ground Correct answer.
  2. The parasitic draw on the 12 V auxiliary battery
  3. The internal resistance of each individual battery module
  4. The current flowing to the traction motor

Explanation

The HV system is deliberately isolated from the chassis, so a resistance drop between HV conductors and ground signals an insulation fault. The monitor tracks that isolation resistance and sets a fault when it falls below a threshold. This protects occupants and technicians from touching a chassis that has become live.

Question 23High-Voltage System Safety Practices and Personal Protective Equipment

Which sequence correctly de-energizes a high-voltage system for service?

  1. Disconnect the 12 V battery, wait five minutes, then touch the cable
  2. Verify zero volts, remove the service disconnect, then don the gloves
  3. Disable per OEM procedure, remove the disconnect, wait, verify zero volts Correct answer.
  4. Remove the service disconnect, verify zero volts, then wait the specified time

Explanation

The approved order is to disable the system as the manufacturer directs, isolate it by removing the service disconnect, allow the specified bleed-down time, and only then verify zero voltage at the point of work. Verification always comes after the wait, never before. Touching a conductor is never a test method.

Question 24High-Voltage System Safety Practices and Personal Protective Equipment

Step and touch potentials are a concern primarily when:

  1. A vehicle is parked on a two-post lift
  2. A battery is charged to 100% state of charge
  3. A person is near a grounded object during an HV fault Correct answer.
  4. Rubber gloves are worn under leather protectors

Explanation

When fault current flows into the earth or a grounded structure, voltage gradients develop across the ground surface and across a person's body. Step potential appears between the feet and touch potential between hand and feet. The risk depends on the fault path, not on lift position or state of charge.

Question 25High-Voltage System Safety Practices and Personal Protective Equipment

Before an insulation resistance test is run on a high-voltage cable with a megohmmeter, the technician must:

  1. Set the meter to the current function
  2. Leave the system energized so the meter can compare voltages
  3. Connect the test lead to the chassis while the pack is live
  4. Isolate the circuit and disconnect sensitive electronics Correct answer.

Explanation

An insulation tester applies a high test voltage that can destroy control modules and other sensitive electronics connected to the circuit. The circuit must be isolated, verified de-energized, and the electronics disconnected first. The meter is used on its insulation resistance setting, not on current.

Question 26High-Voltage System Safety Practices and Personal Protective Equipment

Before beginning work on or near an energized high-voltage system, which of these personal items should a technician remove?

  1. Prescription eyeglasses with plastic frames
  2. Non-metallic safety-toe work boots
  3. A cotton undershirt worn beneath the uniform
  4. A metal wristwatch and a ring Correct answer.

Explanation

Conductive articles such as rings, metal watches, bracelets and metal-framed eyewear can bridge live conductors or create a low-resistance path through the body, so they are removed before high-voltage work. Non-metallic clothing and footwear do not create that path.

Question 27High-Voltage System Safety Practices and Personal Protective Equipment

Which garment is acceptable as a base layer beneath arc-rated clothing when working on an energized high-voltage system?

  1. A cotton long-sleeve shirt Correct answer.
  2. A nylon compression top
  3. A spandex-blend undershirt
  4. A polyester athletic shirt

Explanation

Arc-rated PPE protects only if the layers beneath it will not melt and fuse to the skin when exposed to arc heat. Natural-fiber garments such as cotton are the accepted base layer, while meltable synthetics are avoided.

Question 28High-Voltage System Safety Practices and Personal Protective Equipment

Rubber insulating gloves used for high-voltage work must be worn together with which item?

  1. Cotton liners used in place of the outer glove
  2. Leather protectors worn over the rubber glove Correct answer.
  3. A second pair of rubber gloves worn underneath
  4. Disposable latex over-gloves worn on top

Explanation

Leather protectors are worn over rubber insulating gloves to resist cuts, abrasion and punctures that would destroy the dielectric integrity of the rubber. The rubber glove remains the insulating barrier; the protector preserves it.

Question 29High-Voltage System Safety Practices and Personal Protective Equipment

Rubber insulating gloves that are in active service must receive an electrical retest at what maximum interval?

  1. Every 30 days
  2. Every 12 months
  3. Every 6 months Correct answer.
  4. Every 3 months

Explanation

In-service rubber insulating gloves must be electrically retested every 6 months; insulating sleeves are retested at 12-month intervals. The shorter interval applies to gloves because they see the most mechanical wear.

Question 30High-Voltage System Safety Practices and Personal Protective Equipment

Before relying on a voltage detector to confirm that a high-voltage bus is de-energized, the technician should:

  1. Verify the detector on a known live source and re-verify it after testing the bus Correct answer.
  2. Compare the detector's reading with the vehicle's dash voltage display
  3. Press the detector's self-test button and trust the pass indication alone
  4. Confirm only that the detector's battery indicator shows a full charge

Explanation

Proving the detector on a known live source before the test, and again afterward, guards against a failed or misapplied instrument producing a false zero reading. Self-tests and battery indicators do not prove the sensing circuit works.

Question 31High-Voltage System Safety Practices and Personal Protective Equipment

Which practice is required when performing work on an energized high-voltage system?

  1. Posting a written note at the front desk describing the work
  2. Leaving a shop radio on so that help can be called by voice
  3. Working alone so that no other person is exposed to the hazard
  4. Having a second person present who can isolate power and summon help Correct answer.

Explanation

High-voltage work is not performed alone; a second trained person must be present to de-energize the system and provide or summon emergency aid if the worker is incapacitated. A written note or radio does not satisfy that role.

Question 32High-Voltage System Safety Practices and Personal Protective Equipment

A technician finds a chafed orange high-voltage cable with conductor strands exposed. The correct action is to:

  1. Continue the job but wear Class 0 gloves whenever near the cable
  2. Wrap the damaged area with electrical tape and complete the repair
  3. Stop work, keep clear, and de-energize the system before repairing the cable Correct answer.
  4. Tag the vehicle and finish the job, reporting the damage at end of shift

Explanation

Exposed conductors defeat the insulation system and create a direct shock and arc hazard, so the circuit must be de-energized before any contact or repair. Tape is not a repair for high-voltage cable insulation.

Question 33High-Voltage System Safety Practices and Personal Protective Equipment

Why should PPE selection for a 400 V DC high-voltage bus not rely only on AC arc flash assumptions?

  1. The vehicle's high-voltage interlock will extinguish any DC arc within milliseconds
  2. A DC arc has no current zero to extinguish it, so it can sustain longer Correct answer.
  3. DC systems are always limited to the battery short-circuit current for a single cycle
  4. DC arc flash has been shown to be impossible at voltages below 600 volts

Explanation

Alternating current passes through zero every half cycle, which helps extinguish an arc; direct current has no such zero crossing, so a DC arc can be self-sustaining. Because incident energy depends on arc duration as well as current, DC systems require DC-based hazard analysis and matching PPE.

Question 34High-Voltage System Safety Practices and Personal Protective Equipment

A rubber insulating glove feels tacky and shows swelling across the palm. The glove should be:

  1. Cleaned with solvent and returned to the tool crib
  2. Kept in use only for circuits below 100 volts
  3. Removed from service and replaced Correct answer.
  4. Returned to service after a successful air test

Explanation

Tackiness and swelling indicate chemical contamination or ozone degradation of the rubber, which reduces dielectric strength throughout the glove. An air test detects punctures and tears, not degraded material, so the glove is retired from service.

Question 35High-Voltage Battery Systems Service and Diagnosis

How is the nominal voltage of a high-voltage battery pack determined when cells are connected in series?

  1. Multiply the nominal cell voltage by the number of cells in series Correct answer.
  2. Divide the nominal cell voltage by the number of modules
  3. Multiply the nominal cell voltage by the number of parallel strings
  4. Add the amp-hour capacity of every cell in the pack

Explanation

Series-connected cells add their voltages while the amp-hour capacity stays equal to that of a single cell. The pack nominal voltage is therefore the nominal cell voltage multiplied by the series cell count. Parallel strings increase capacity, not voltage.

Question 36High-Voltage Battery Systems Service and Diagnosis

Which component limits the current that flows while the battery contactors are closing?

  1. The service disconnect plug
  2. The pack fuse
  3. The Hall-effect current sensor
  4. The precharge resistor Correct answer.

Explanation

The precharge resistor is placed in series with a precharge contactor so the inverter capacitors charge gradually, limiting inrush current. Once the inverter-side voltage approaches pack voltage, the main contactors close.

Question 37High-Voltage Battery Systems Service and Diagnosis

What is the maximum working voltage rating of Class 0 insulating gloves?

  1. 250 V AC
  2. 1000 V AC Correct answer.
  3. 7500 V AC
  4. 500 V AC

Explanation

Class 0 gloves are rated for a maximum use voltage of 1000 V AC (1500 V DC), which covers most passenger EV packs. Higher classes are needed only for higher system voltages.

Question 38High-Voltage Battery Systems Service and Diagnosis

What is the primary purpose of the manual service disconnect on a high-voltage battery?

  1. To reset the battery management system
  2. To open the HV circuit for service Correct answer.
  3. To charge the pack from the grid
  4. To balance the cells during service

Explanation

Removing the manual service disconnect opens the high-voltage circuit and on many designs splits the pack into lower-voltage sections. This creates a safer condition for service work. It is not a charging, balancing, or reset device.

Question 39High-Voltage Battery Systems Service and Diagnosis

Which instrument is used to measure insulation resistance of the high-voltage system?

  1. Clamp-on ammeter
  2. Insulation tester (megohmmeter) Correct answer.
  3. Non-contact infrared thermometer
  4. Digital storage oscilloscope

Explanation

An insulation tester applies a high DC test voltage and displays resistance in megohms, which reveals leakage paths to chassis. An ordinary ohmmeter cannot apply enough voltage to evaluate HV insulation.

Question 40High-Voltage Battery Systems Service and Diagnosis

Which function does the battery management system perform?

  1. Stepping up pack voltage to the inverter
  2. Regulating cabin air temperature
  3. Monitoring cell voltages and temperatures Correct answer.
  4. Converting DC pack voltage to three-phase AC

Explanation

The BMS monitors cell voltages, module temperatures, and pack current, and uses that data to control contactors, balancing, and power limits. Voltage conversion and cabin climate control are handled by other systems.

Question 41High-Voltage Battery Systems Service and Diagnosis

At what state of charge should a lithium-ion HV pack be stored for an extended period?

  1. 100 percent
  2. Exactly 90 percent
  3. About 30 to 50 percent Correct answer.
  4. 0 percent

Explanation

Lithium-ion packs age fastest at very high and very low states of charge, so long-term storage is specified around the mid range. A 30 to 50 percent level also leaves margin for self-discharge.

Question 42High-Voltage Battery Systems Service and Diagnosis

What does the orange color of a cable in an electric vehicle indicate?

  1. It is a dedicated ground strap
  2. It is a fiber-optic communication line
  3. It may carry high voltage Correct answer.
  4. It carries 12-volt chassis power

Explanation

Orange is the industry-standard identifier for high-voltage cabling, warning that the conductor may be energized at pack voltage. Such cables must never be cut, probed, or disconnected without following HV safety procedures.

Question 43High-Voltage Battery Systems Service and Diagnosis

During an insulation resistance test of a 400 V battery pack, the meter displays 0.01 MΩ between the positive terminal and chassis ground. What does this indicate?

  1. A normal reading for a pack of this voltage
  2. The pack is fully charged and healthy
  3. The meter leads are reversed
  4. An insulation fault in the pack or cabling Correct answer.

Explanation

0.01 MΩ equals 10 kΩ, while a 400 V pack is commonly required to show at least 100 Ω per volt, or about 40 kΩ. A reading this low means a leakage path exists and the pack must be isolated and diagnosed.

Question 44High-Voltage Battery Systems Service and Diagnosis

A pack shows 94 cells at 3.85 V and two cells at 3.55 V after a full charge. What is the most likely interpretation?

  1. All cells are within acceptable balance limits
  2. The pack is overcharged and must be discharged
  3. The two low cells should be investigated Correct answer.
  4. The BMS is reading temperatures incorrectly

Explanation

A 300 mV spread after charging is far outside the normal balancing window, which is typically a few tens of millivolts. Two persistently low cells point to weak or failing cells that need further testing.

Question 45High-Voltage Battery Systems Service and Diagnosis

During the constant-voltage phase of a lithium-ion charge, what happens to the charge current?

  1. It reverses to balance the cells
  2. It rises as the pack fills
  3. It tapers down near full charge Correct answer.
  4. It stays constant until the charge ends

Explanation

The charge begins in constant current until the pack reaches its voltage limit, then switches to constant voltage. In that phase the current decays as the cells approach full charge, and the charge terminates when current falls below a set threshold.

Question 46High-Voltage Battery Systems Service and Diagnosis

After the contactors are commanded open, a technician measures full pack voltage at the inverter terminals. What is the most likely cause?

  1. Current sensor calibration error
  2. Precharge resistor open circuit
  3. BMS lost CAN communication
  4. A main contactor is welded closed Correct answer.

Explanation

If pack voltage is still present downstream after an open command, the isolation device is not actually opening. A welded main contactor keeps the circuit closed and is a serious safety hazard.

Question 47High-Voltage Battery Systems Service and Diagnosis

Which meter safety rating is required for probing an energized 400 V DC battery circuit?

  1. CAT I, 300 V
  2. CAT II, 250 V
  3. CAT III, 600 V or higher Correct answer.
  4. Any meter with a 10 A fuse

Explanation

CAT III ratings apply to fixed installations and distribution circuits and include a voltage rating that must exceed the circuit voltage. A 400 V pack therefore requires a meter rated at least CAT III 600 V.

Question 48High-Voltage Battery Systems Service and Diagnosis

Which condition is an early warning of battery thermal runaway?

  1. A slow drop in pack voltage during charging
  2. A code for low 12-volt battery voltage
  3. Rising cell temperature with a solvent odor Correct answer.
  4. Increased coolant flow through the pack

Explanation

Thermal runaway is preceded by cell overheating and venting of electrolyte vapor, which has a distinct sweet or solvent-like smell. Rising temperature plus that odor calls for immediate evacuation and isolation of the vehicle.

Question 49High-Voltage Battery Systems Service and Diagnosis

How does passive cell balancing work?

  1. It moves charge from high cells to low cells through a capacitor
  2. It disconnects low cells from the string during charging
  3. It bleeds excess energy from higher cells as heat Correct answer.
  4. It raises the charge voltage to top off weaker cells

Explanation

Passive balancing switches a resistor across the higher-voltage cells so their extra energy is dissipated as heat while the pack charges. The pack ends the charge with all cells at a similar voltage, though energy is wasted.

Question 50High-Voltage Battery Systems Service and Diagnosis

A vehicle with a collision-damaged HV battery is in the shop. Where should the pack be stored while awaiting repair?

  1. In a quarantine area away from combustibles Correct answer.
  2. On a wooden pallet inside the parts storage room
  3. Beside the tire storage rack in the main shop area
  4. Inside the customer vehicle until parts arrive

Explanation

A damaged pack may have compromised cells that can vent or ignite later, so it must be isolated in a designated quarantine area away from other vehicles and combustible materials. The area should be monitored until the pack is evaluated or shipped out.