Five free practice questions on HV supporting systems: content area E of the ASE L3 Light Duty Hybrid/Electric Vehicle Specialist test, 6 of its 45 scored questions (13.3%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.
01The questions
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A battery electric vehicle is charging from a Level 2 EVSE when it arrives for an HV cabin heater replacement. The manufacturer's HV disable procedure begins by ending the charge session and unplugging the charge connector. Why does this step come first?
- Unplugging resets the battery controller so the pack reads 0 volts
- EVSE voltage would reach the heater through the 12-volt system
- Charging keeps the HV contactors closed and the bus energized
- The charge inlet's pilot wire would short when the MSD is pulled
Show the answer
C. Correct. While a charge session is under way the HV battery is connected to the HV bus and the on-board charger is supplying it, so the heater's feed is live. Ending the session and unplugging lets the contactors open before the rest of the manufacturer's disable steps begin.
Why not the others
A. Nothing makes the pack itself read 0 volts; its modules always hold their voltage. Unplugging matters because it ends the charge session that keeps the contactors closed and the HV bus live.
B. The EVSE's AC goes only to the on-board charger, not into the 12-volt system. The reason is on the HV side: charging keeps the contactors closed and the bus energized.
D. The pilot circuit is a low-voltage signal between EVSE and vehicle and is not affected by removing the MSD. The connector is unplugged first because charging keeps the HV bus energized.
ID L3-E-003 · Task L3-E-1 (ASE task list)
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A customer's Level 2 EVSE will not charge the vehicle, and the technician wants to check the EVSE's line voltage and pilot signal on the EVSE alone, without a vehicle connected. Which of these lets that be done?
- An EVSE test adapter that simulates a vehicle's pilot states
- A DMM probed into the EVSE connector's pins with no load
- An insulation tester across the connector's power pins
- A clamp meter around the EVSE cable with the connector unplugged
Show the answer
A. Correct. An EVSE closes its output only after a connected vehicle signals on the pilot line that it is present and ready. A test adapter plugs into the EVSE connector, steps through those vehicle states and brings the pilot and line voltage out to test jacks for a meter or scope.
Why not the others
B. With nothing connected, a working EVSE keeps its output relay open, so its power pins read 0 volts and the test shows nothing about the EVSE. A test adapter that imitates a vehicle is needed to make it switch on.
C. An insulation tester checks insulation on de-energized circuits and does not show whether the EVSE delivers voltage or a pilot signal. Its test voltage applied across the pins can also harm the EVSE's electronics.
D. No current can flow with the connector unplugged, and the EVSE will not switch its output on without a vehicle signal. An adapter that simulates the vehicle is what makes the output testable.
ID L3-E-006 · Task L3-E-3 (ASE task list)
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A pickup's cab and bed 120 VAC outlets are fed in parallel from one output of a single outlet inverter, and the bed outlet is a ground-fault (GFCI) receptacle. The bed outlet gives no output while the cab outlet works normally. Any of these could be the cause EXCEPT:
- a tripped ground-fault circuit in the bed receptacle.
- an open in the wiring from the inverter to the bed outlet.
- an overload shutdown of the outlet inverter.
- corroded terminals at the bed outlet from water entry.
Show the answer
C. Correct. Both outlets hang on the same inverter output, so an inverter overload shutdown would cut the cab outlet as well, and the cab outlet works. The fault lies between the inverter and the bed outlet.
Why not the others
A. A GFCI receptacle that has tripped opens its own output and stays off until it is reset, while the cab outlet on the same inverter keeps working. It could be the cause.
B. A break in the branch to the bed outlet removes power from that outlet alone, leaving the cab outlet working. It could be the cause.
D. A bed outlet is exposed to rain and washing; corrosion on its terminals can open the circuit at that outlet only. It could be the cause.
ID L3-E-008 · Task L3-E-5 (ASE task list)
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Why does a battery electric vehicle's heat pump use less HV battery energy to warm the cabin than a resistive (PTC) heater giving the same amount of heat?
- Its compressor turns electricity into heat more efficiently
- It moves heat in from outside instead of making all of it
- It recirculates cabin air so less heat leaves the vehicle
- It runs from the 12-volt system rather than the HV battery
Show the answer
B. Correct. A resistive heater turns each watt of electricity into one watt of heat. A heat pump uses its compressor to pick up heat from outdoor air (or from other components) and release it in the cabin, so it delivers more heat than the electrical energy it uses.
Why not the others
A. A resistive heater already turns essentially all of its electrical energy into heat, so nothing beats it at that conversion. The heat pump's saving comes from heat it moves in from outside, not from a better conversion.
C. Recirculation is a door setting that either kind of heater can use. The heat pump's advantage is that it moves heat into the cabin rather than making all of it from electricity.
D. A heat pump's compressor is an HV electric compressor, and the 12-volt system is itself supplied from the HV battery through the DC/DC converter. The saving comes from moving heat, not from the supply it runs on.
ID L3-E-011 · Task L3-E-7 (ASE task list)
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A hybrid's A/C compressor is an electrically driven scroll unit with its motor and inverter built in and no belt drive. With A/C requested in READY TO DRIVE, it never runs. Any of these could be the cause EXCEPT:
- an open circuit in the compressor clutch coil.
- refrigerant pressure below the low-pressure limit.
- an open fuse in the compressor's HV supply.
- a failed inverter inside the compressor.
Show the answer
A. Correct. An electrically driven scroll compressor has no clutch: its built-in inverter starts, runs and stops the motor, so there is no clutch coil to fail. A clutch belongs to a belt-driven compressor.
Why not the others
B. The climate controls read the refrigerant pressure and will not run the compressor below their low-pressure limit, to protect it when the charge is low. It could keep the compressor from running.
C. The compressor's motor runs on HV through its built-in inverter, so an open HV fuse leaves it with no power to run. It could be the cause.
D. The built-in inverter changes HV DC into the three-phase AC that turns the motor; if it fails, the motor cannot be driven. It could be the cause.
ID L3-E-014 · Task L3-E-8 (ASE task list)
02Answer key
| Question | Answer |
|---|---|
| Q1 | C |
| Q2 | A |
| Q3 | C |
| Q4 | B |
| Q5 | A |
03What area E covers
This content area covers the systems the high-voltage battery runs besides the drive: driver displays and energy monitors, cabin heating and cooling with the electric A/C compressor and its oil, telling a regenerative braking fault from a hydraulic one, coolant loop service, charging problems with EVSE, 120/240 VAC outlets and vehicle-to-grid power, and electric power steering.
The ASE test specification calls this content area “Supporting Systems”. It carries 6 of the 45 scored questions, 13.3% of the test.
- Read the energy display and charge settings
- Diagnose HV cabin heaters and heat pumps
- Test the electric A/C compressor and choose its oil
- Separate regenerative braking faults from hydraulic brake faults
- Leak-test, fill and service liquid cooling loops
- Diagnose EVSE charging problems and supply circuits
- Diagnose 120/240 VAC outlets and vehicle-to-grid power
- Diagnose electric power steering assist faults
04What the questions turn on
Regeneration does not pulse the pedal
Regenerative torque is controlled electrically at the MG and does not act on the hydraulic system. A pulsing pedal or a pull in firm stops points to the friction brakes, such as rotor thickness variation or a seized caliper slide pin.
Keep PAG oil out
An electric A/C compressor takes the oil the manufacturer specifies, such as POE. PAG oil lowers the compressor's insulation resistance, so a machine shared with belt-driven systems is flushed of PAG oil as its maker directs before its injection path is used.
Normal behavior is not a fault
Every charge ending at 80 percent with healthy cells and normal session endings can be the owner's charge-limit setting. A plug-in hybrid showing 0 miles of electric range with charge left has reached the reserve it keeps for hybrid use.
Outlet circuits count as high voltage
High voltage means over 60 VDC or 30 VAC, so a 120 VAC outlet circuit qualifies. A stepped-sine outlet inverter is read with a true-RMS meter, and a motor's starting surge can trip an overload that a larger steady load does not.
05The other content areas
The L3 test has five content areas. Each has its own page of free questions:
The ASE L3 Light Duty Hybrid/Electric Vehicle Specialist practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.
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