Your FREE ASE L3 Flashcards 2026 – 200+ Cards

The industry-standard color code for high-voltage conductors. Treat any orange cable or connector as energized at dangerous levels (200-450 V) until verified at zero.

On a light-duty hybrid/EV, the propulsion voltage — roughly 200-450 V DC — high enough to be lethal. Always treated as live until de-energized and verified.

Power down and remove the key/fob, disconnect the 12-volt battery, remove the HV service disconnect, wait the OEM bleed-down time, then verify zero energy.

A removable device on or near the battery pack that manually breaks the HV circuit, usually by splitting the pack into two non-lethal halves.

Verifying zero energy with a CAT III meter: read a known live source, then the HV test points (~0 V), then the live source again to prove the meter still works.

A multimeter and leads rated to withstand the transient overvoltage spikes of high-energy circuits. CAT III or higher is required for measuring HV on hybrids/EVs.

Rubber insulating gloves rated to 1,000 V AC (ASTM D120) — the minimum for light-duty HV service. Worn with leather protectors and inspected before each use.

Higher-rated insulating gloves: Class 1 to 7,500 V AC, Class 2 to 17,000 V AC — for utility-grade work beyond light-duty automotive HV.

Leather overgloves worn over rubber insulating gloves to protect them from cuts and abrasion that would destroy their insulating value.

A rapid release of electrical energy when current arcs across a gap or short, producing intense heat, light, and a pressure blast capable of severe burns.

PPE that protects against the heat and pressure of an arc flash; worn with insulating gloves per the OEM and job hazard assessment when contacting exposed HV.

After the HV circuit opens, the inverter's DC-link capacitors still hold a lethal charge; the OEM-specified wait (often 5-10 min) lets them discharge before verifying zero.

The HV system is electrically isolated from the chassis. A loss of isolation — insulation resistance far below spec — is a shock hazard and sets an isolation fault.

Measures isolation resistance between HV components and chassis ground. Healthy readings are high megohms; a low (kilohm) reading signals loss of isolation.

A resistance reading much lower than the manufacturer's minimum (often low kilohms) between the HV pack and chassis indicates a loss of HV isolation.

Removing the low-voltage supply prevents the HV contactors from being commanded closed again while you work on the de-energized system.

Never rely on a dashboard warning light. Proof of a safe system is a live-dead-live measurement with a CAT III meter after de-power and bleed-down.

Nickel-metal hydride (NiMH) or, increasingly, lithium-ion cells in series (and parallel) to reach pack voltage. Lithium-ion is denser but more heat/charge sensitive.

Nickel-metal hydride — rugged, common in early hybrids, less energy-dense than lithium-ion, and not prone to a true memory effect.

Unlike NiCad, NiMH is not prone to true memory effect. Reduced capacity is far more likely from cell aging, internal resistance, or imbalance.

Higher energy density than NiMH but sensitive to heat, over-charge, and over-discharge; relies on careful thermal management and BMS control.

Electronics that monitor cell voltages and temperature, balance cells, manage state of charge, and limit charge/discharge to protect the HV battery.

Remaining HV battery energy as a percent of usable capacity, kept by the BMS within a protective window (not 0-100% of physical capacity).

The BMS equalizes individual cell charge so no cell is over- or under-charged, protecting pack life and capacity.

Usually from cell aging, increased internal resistance, or cell imbalance — not from NiMH memory effect.

Measure individual module voltages with a CAT III meter (system de-energized) and compare each to the rated value to find a weak or shorted module.

The conductive bars linking battery cells/modules. Loose or corroded bus bars raise resistance and hurt performance; torque to spec and keep clean.

Many lithium-ion packs use a liquid cooling loop to control cell temperature; coolant level/condition and pump flow affect battery health and life.

Store a removed lithium-ion pack per the OEM: at a moderate state of charge, in a cool, dry, fire-safe location away from ignition sources.

A full, cold, or near-SOC-limit battery limits how much regenerative energy it can accept — often normal, BMS-protective behavior.

High-voltage components carry warning labels and orange marking; observe them and the OEM procedure before any contact.

The category rating, not just max voltage, decides survival of transient spikes. A high-voltage but low-CAT meter can fail catastrophically on HV.

Electric shock (current through the body) and arc flash (a rapid energy release that burns and blasts). Both demand correct PPE and de-energizing.

Before HV service, set the parking brake and chock the wheels so the vehicle can't move while powered down for work.

Removing the service disconnect typically divides the pack so neither half is at the full lethal pack voltage during service.

Treat the HV system as live, use insulated tools and PPE, follow OEM cut/loop locations, and never bridge HV terminals or improvise grounding.

Tools rated and labeled for high-voltage work used when there is any risk of contacting energized HV; part of layered HV protection.

After verifying zero, probe across module terminals with a CAT III meter set to DC volts and compare to the rated nominal voltage.

A pack-to-chassis insulation reading well above the OEM minimum, in the high megohm range, indicates good isolation.

Heat is the enemy of lithium-ion cells; the cooling system and BMS thermal limits protect life, capacity, and safety.

Any HV-powered accessory (A/C compressor, heater, cables) is marked orange and must be treated as live until verified at zero.

Confirm HV isolation to chassis is healthy (high megohms) as part of diagnosing shock-hazard or isolation-fault complaints.

Moving the key/fob out of range during de-power ensures the vehicle can't wake and close the HV contactors.

A 12-volt test light can't confirm HV module voltage or zero energy; use a CAT III meter set to DC volts for HV measurements.

Opening the HV circuit does not instantly make it safe — DC-link capacitors hold a lethal charge until the bleed-down time passes.

Inspect insulating gloves for damage before each use; a pinhole or cut destroys their protection. Periodic dielectric testing is also required.

An uncontrolled exothermic reaction in a lithium-ion cell; managed by thermal control and BMS limits, and a reason for careful storage/handling.

Comparing each module's voltage to its rated value (after verifying zero pack hazard at the test point) finds a weak or shorted module.

A liquid-cooled pack relies on correct coolant and flow; low or degraded coolant can let cells overheat and lose performance.

The HV system is intentionally isolated (ungrounded) from the chassis so a single fault doesn't energize the body; isolation monitoring guards this.

Retrieve codes with a scan tool through the data link; do not improvise HV probing to chase a code — use the tool and OEM data.

The HV service disconnect is commonly under a rear seat, trunk/cargo floor, or an access panel near the battery pack.

Cordon off an HV work area and post signage so others don't approach an energized or exposed HV system during service.

Some OEMs require a trained second person nearby during exposed HV work to respond in an emergency.

Insulating gloves must be re-tested periodically (commonly every 6 months) and inspected before each use; failed gloves are removed from service.

Remove rings, watches, and metal jewelry before HV work; conductive items create a shock and arc-flash risk.

Inspect orange HV cables for chafing or damage; a compromised cable can cause loss of isolation or a shock hazard.

Lithium-ion packs have venting and thermal safeguards; never block vents, and handle damaged packs per OEM fire-safety procedures.

An isolation fault can occur in service; the vehicle warns the driver and may reduce power to limit the shock hazard.

Some packs are air-cooled; a blocked intake or failed fan lets the pack overheat and lose performance.

Master high-voltage safety first (tested everywhere), then weight study toward Power Electronics and the HV Battery System, the two largest scored areas.

Power-electronics module that converts battery DC to three-phase AC to drive the traction motor, and AC back to DC during regen and charging.

Insulated-gate bipolar transistor — the high-current switching device inside the inverter that synthesizes the AC waveform. Overheats if cooling fails.

The inverter feeds three AC phases to the motor; controlling their timing and amplitude sets motor torque and speed.

Steps the high-voltage battery (200-450 V) down to about 12-14 V to charge the 12-volt battery and run accessories — replaces the alternator.

If it fails, the 12-volt battery discharges and low-voltage systems (lights, modules, contactor coils) lose power.

Relays inside the battery pack that connect or isolate the HV battery from the rest of the vehicle.

Limits the inrush current as the HV contactors close, protecting the contacts and the DC-link capacitors from damage.

A low-voltage safety circuit run in series through HV connectors and covers. Opening any of them breaks the loop and de-energizes the HV system.

A damaged or open interlock loop (e.g., a bent connector pin) can set a false interlock/isolation fault and keep the HV system from energizing.

The assembly housing the inverter (and often the DC-DC converter and controls) that manages high-current motor drive.

Often a dedicated liquid loop; poor heat-sink contact or failed thermal paste causes IGBT overheating — a common inverter failure.

DC-link capacitors smooth the DC bus and hold a lethal charge; the bleed-down wait must elapse before verifying zero in the power electronics.

Often points to the inverter or its motor-control outputs rather than the pack; verify three-phase outputs and inverter cooling.

During regen the inverter rectifies the motor-generator's AC output to DC to charge the HV battery.

De-energize and verify zero, check cooling, inspect HV connectors/HVIL, then test the inverter's outputs and control signals per OEM.

Open contactors isolate the battery for safety; closed contactors connect it to the inverter and the rest of the HV system.

They sit in the HVIL; opening one breaks the interlock loop, which commands the contactors open and drops the high voltage.

Converts AC from a charging station to DC to charge the HV battery; in some EVs it is bidirectional for vehicle-to-load/grid.

External DC charging feeds the pack directly, bypassing the onboard AC charger, for much faster charging on capable vehicles.

Transfers heat from the IGBTs/power module to the cooling system; degraded paste or poor contact causes overheating and failure.

Coordinates engine, motor-generators, battery, and braking so power flows seamlessly; many faults are network/communication-related.

A stuck-closed (welded) contactor keeps the HV connected when it should isolate — a serious safety fault detected by the BMS.

If pre-charge fails, contactors see high inrush; the system may refuse to close the main contactors to prevent damage.

Loss of DC-to-AC conversion (a failed main inverter module) most directly stops the traction motor from receiving drive power.

Insufficient cooling — failed coolant flow, poor heat-sink contact, or degraded thermal paste — leads to IGBT overheating and failure.

Verify the DC-DC converter output (about 12-14 V) when the 12-volt battery won't stay charged on a hybrid/EV with no alternator.

Disconnecting an HV connector can trigger the HVIL, set a fault, and display an HV warning — by design, to protect the technician.

When reinstalling a power module after replacing thermal interface material, follow torque and seating specs so cooling contact is correct.

A power inverter module may mismanage motor power from a control/sensor fault, overheating, or a failed switching device (IGBT).

With OEM procedure, verify balanced three-phase outputs from the inverter to confirm it can drive the motor.

Many hybrid faults are network/communication issues between modules; check bus integrity before condemning HV hardware.

The 12-volt system energizes the contactor coils; a weak 12-volt supply can prevent the contactors from closing to enable HV.

Inverter and converter often share or have dedicated liquid cooling; check coolant level, flow, and the pump for overheating faults.

Stabilizes the DC voltage feeding the inverter; its stored charge is the reason for the mandatory bleed-down wait.

Low-voltage (12 V) runs controls/accessories; high-voltage (200-450 V) drives propulsion. The DC-DC converter bridges them.

A hybrid/EV has no belt-driven alternator; the DC-DC converter charges the 12-volt battery from the HV pack instead.

On power-up the BMS typically closes a pre-charge path first to charge the DC-link capacitors, then closes the main contactors.

An electric machine that acts as a motor (adding drive torque) and as a generator (producing electricity during regen or engine-driven charging).

Hybrids often use two: one as a starter/generator (engine start, charging) and one as the main traction motor.

Most traction motors are three-phase AC (permanent-magnet or induction) fed by the inverter; the phase timing sets torque and speed.

A planetary-gear transaxle that blends engine and electric power continuously, behaving like a CVT so the engine runs in its efficient range.

The sun, planet carrier, and ring gears combine engine and two motor-generators to split power between driving the wheels and generating.

Many battery EVs use a single fixed-ratio reduction gear from the motor to the wheels — no multi-speed transmission needed.

A power-split hybrid can creep forward in Drive using electric motor torque alone, with the engine off.

A megohmmeter test between each motor winding and the case checks for loss of isolation; a low reading means insulation breakdown.

Near-zero resistance between a winding and the motor case means the insulation has broken down — a shock hazard and motor failure.

Reports the motor rotor's position so the inverter can time the AC phases; a fault causes rough running or no drive.

A steady whine that rises with road speed usually points to gear or bearing wear inside the hybrid transaxle.

Use the OEM-specified fluid and procedure; the electric drive unit and gears rely on correct lubrication and, often, shared cooling.

Always de-power and verify zero before removing or opening an HV motor or its inverter connections.

The electric drive unit may share a cooling circuit with the power electronics; a coolant problem can affect both.

A clicking noise from the front on turns points to a worn outer CV joint, just as on a conventional FWD vehicle.

Diagnose systematically: confirm HV ready, check for faults, verify inverter output and the reduction-gear/drive-unit mechanically.

Uses magnets on the rotor; efficient and compact, common in EV traction motors. Back-EMF from spinning magnets is present even unpowered.

Uses induced rotor currents instead of magnets; rugged and used by some EVs for traction.

Mechanical noises (whine, growl, click) point to gears, bearings, or CV joints; electrical faults show as no/rough drive or isolation codes.

The engine can spin a motor-generator to recharge the HV pack, separate from regen — a hybrid maintains its own state of charge.

A spinning permanent-magnet motor generates voltage (back-EMF) even when unpowered, so its terminals can be live while the wheels turn.

A rotary position sensor on the traction motor that tells the inverter the rotor angle for precise AC phase control.

Reduction gearing matches the high-speed electric motor to wheel speed and multiplies torque; wear shows as whine or growl.

Clicking on turns = CV joint; a steady speed-related whine = gear/bearing wear — distinguish before disassembly.

A power-split hybrid can creep on electric torque alone in Drive; the engine starts only when more power or charging is needed.

High winding-to-ground resistance (megohms) = healthy; a low reading means insulation breakdown to the case and a failed or unsafe motor.

The motor's three phases should be balanced; large resistance or insulation differences between phases indicate a winding fault.

Electric drive is efficient and provides instant torque; regen recovers energy on deceleration, improving overall vehicle efficiency.

On a BEV with one reduction gear, a no-move fault means checking HV readiness, inverter output, and the drive unit mechanically.

Series: engine drives a generator only. Parallel: engine and motor drive the wheels. Series-parallel (power-split): both, blended by a planetary set.

Uses a small motor-generator (often 48-volt) to assist and enable start-stop, but can't drive on electric power alone.

Can drive on electric power alone for short distances, blend power, and recharge via regen and the engine — e.g., a power-split hybrid.

A hybrid with a larger battery that plugs in for meaningful electric-only range, then operates as a hybrid once the charge is used.

An all-electric vehicle with no internal-combustion engine; propulsion is entirely from the HV battery, inverter, and traction motor.

In many power-split hybrids one motor-generator (MG1) primarily generates and starts the engine, while MG2 mainly drives.

The larger motor-generator (MG2) provides the main drive torque and the regenerative braking generation.

Use a megohmmeter on de-energized windings; compare to spec to confirm isolation between windings and the case before reuse.

Shuts the internal-combustion engine off when it isn't needed (idle, low load) to save fuel; restarted quickly by a motor-generator.

A motor-generator that starts the engine quickly and smoothly and can also generate, replacing a conventional starter and alternator.

Keeps engine coolant circulating while the engine is auto-stopped (a belt-driven pump would stop with the engine).

The hybrid engine starts and stops automatically; interpret performance data knowing the engine may not be running continuously.

A long-term fuel trim well into positive (lean) territory points to a vacuum/air leak or low fuel delivery — same diagnosis as a conventional engine.

After engine or hybrid service, a relearn or verification of auto start-stop and emissions monitors may be required for correct restarts.

Many hybrids use an Atkinson-cycle engine — more efficient but lower power density — because the electric motor fills in torque.

Under light load or low speed a hybrid can drive on the motor alone with the engine off, then restart the engine when more power is needed.

Most hybrids still carry a gasoline engine; conventional engine-performance diagnosis (misfires, trims, sensors) applies within the hybrid context.

A motor-generator spins the engine to speed before fueling for a smooth restart; a rough restart can signal an MG, sensor, or control fault.

Frequent engine stops can affect when OBD-II monitors run; a relearn or drive cycle may be needed to set readiness after service.

On a hybrid the engine can be a heat source for the cabin, but with frequent engine-off operation, electric heating is often needed.

Brakes and other systems that relied on engine vacuum may use an electric vacuum pump or brake-by-wire since the engine isn't always running.

A hybrid runs the engine as needed to keep the HV battery within its target SOC window, independent of plugging in.

Hybrid engines may share or coordinate cooling with the power electronics and drive unit; check the correct loop for a given complaint.

On the hybrid's engine, conventional timing references like TDC still apply for valve timing and engine-performance diagnosis.

Atkinson trades peak power for efficiency by effectively shortening the compression stroke; hybrids use it because the motor adds torque.

An electric coolant pump maintains flow during auto-stop so the engine and heater core stay at temperature for the next restart.

After an auto-stop, confirm the engine restarts smoothly and on time; a delayed/rough restart can mean an MG, sensor, or control issue.

With the engine off, the HV battery and DC-DC converter power accessories that an engine-driven belt would normally run.

Conventional misfire diagnosis applies, but interpret freeze-frame data knowing the engine may stop/start under hybrid control.

Hybrids still have a conventional fuel system; sealed/evaporative systems may differ slightly to handle long engine-off periods.

In some plug-in hybrids the engine mainly drives a generator to recharge the pack (series operation) rather than the wheels directly.

Hybrids use OBD-II for emissions monitoring and store DTCs; HV and hybrid-specific data may need an enhanced/OEM scan tool.

A snapshot of sensor readings captured when a code set, used to recreate the conditions of an engine or hybrid fault.

The ASE question style: judge each technician's statement separately as true or false, then choose A only, B only, both, or neither.

Recovers kinetic energy during deceleration by back-driving the motor-generator as a generator and charging the HV battery instead of wasting heat.

Electronically blends regenerative and hydraulic friction braking to deliver exactly the deceleration the driver requests.

As the vehicle nears a stop, regen torque fades out and friction braking takes over; poor blending feels inconsistent to the driver.

A full, cold, or near-SOC-limit battery reduces how much regen energy it can accept, so the friction brakes do more of the work.

Use a scan tool to compare commanded versus actual regenerative torque to find why regen is weaker than normal.

Driven by its own HV motor (not a belt), so it can cool the cabin while the engine is off; speed is controlled electronically.

Electric A/C compressors require special electrically non-conductive (POE-type) oil; the wrong oil can cause a loss of HV isolation.

Passes high-voltage current through a ceramic element to make heat for the cabin; effective but a heavy drain on range in cold weather.

Moves heat rather than generating it, so it heats the cabin far more efficiently than a PTC resistance heater, reducing cold-weather range loss.

Provides steering assist electrically; it depends on a healthy 12-volt supply, so a weak 12-volt system can cause heavy or lost assist.

Converts station AC to DC to charge the HV battery; Level 1/2 AC charging uses it, while DC fast charging bypasses it.

A bidirectional onboard charger lets the vehicle discharge HV battery energy back to the grid or to power external loads.

Resistance (PTC) heating draws a lot of HV power; weak heat plus high cold-weather range loss often points to PTC heater operation or a fault.

A vehicle that charges on Level 2 AC but reports a charging fault may have an onboard-charger, communication, or connector problem.

Compared with friction braking, regen recovers kinetic energy and returns it to the HV battery, improving efficiency and reducing brake wear.

Regen can't supply all braking (low speed, full/cold battery, hard stops), so hydraulic friction brakes blend in to complete the stop safely.

Servicing a brake-by-wire system requires the correct OEM procedure and bleed/initialization steps so blending works correctly afterward.

Check for a full/cold battery or a BMS limiting regen acceptance, and compare commanded versus actual regen torque with a scan tool.

Many supporting systems (EPS, contactor coils, modules) need a healthy 12-volt supply kept charged by the DC-DC converter.

Because it is electronically driven, the electric A/C compressor's speed (and cooling capacity) is controlled by the HVAC system, not engine RPM.

A heat pump uses much less energy than a PTC heater for the same cabin heat, preserving more driving range in cold weather.

HV-powered accessories (compressor, heater) are on orange cabling; de-energize and verify zero before servicing them.

Heavy or absent steering assist often traces to a low/weak 12-volt system causing the EPS module to reduce or drop assist.

V2G/V2L needs a bidirectional onboard charger and compatible equipment to safely export HV battery energy.

The HV-powered or HV-aware accessories: regenerative braking, electric A/C and heating, electric power steering, and the charging system.

Strong regen on lift-off lets the driver slow the car with the accelerator alone; friction brakes still finish hard or low-speed stops.

Brake-by-wire still uses hydraulic friction brakes; correct fluid, bleeding, and initialization per OEM are required after service.

Cabin heating (especially PTC), reduced battery performance, and higher rolling losses cut range in cold weather.

Uses a refrigerant cycle to move ambient or waste heat into the cabin, delivering more heat per unit of energy than resistance heating.

Powers low-voltage controls and the contactor coils; kept charged by the DC-DC converter. A dead 12-volt can prevent HV start-up.

AC (Level 1/2) and DC fast-charging connectors differ; the onboard charger handles AC, while DC charging feeds the pack directly.

Strong regenerative deceleration may activate the brake lights even without the friction brakes, for following-driver safety.

Many hybrids/EVs eliminate engine-driven accessory belts, using electric pumps and compressors so accessories run with the engine off.

A scan tool reads pack voltage, SOC, cell/module data, temperatures, and commanded vs actual values to diagnose HV systems without exposure.

Because the engine isn't always running, hybrids supply braking assist via an electric vacuum pump or brake-by-wire system.

Use HV/EV-rated recovery equipment and the correct non-conductive oil; cross-contaminating oils can damage the compressor and isolation.

Heating and cooling draw from the HV battery, so HVAC use directly affects driving range — most in extreme temperatures.

The charger negotiates with the station (e.g., for AC charging); a communication or connector fault can stop charging even if the charger is good.

Compare commanded and actual regen torque and confirm brake-by-wire blending to diagnose inconsistent deceleration complaints.