Five ASE L3 Light Duty Hybrid/Electric Vehicle Specialist practice test questions, answers included.

1. Diagnosis · High-Voltage (HV) Battery System

   On a hybrid, the scan tool shows block 5's voltage dropping from 15.1 volts to 0 volts and back whenever the BMS harness connector is moved, while the other blocks read steady and the BMS's pack voltage reading does not change. Which of these could be the cause?

   1. Worn contacts inside the pack's main positive contactor
   2. An internal open between two of block 5's cells
   3. A failing current sensor in the pack
   4. A loose terminal in block 5's voltage-sense lead
   Show the answer

   D. Correct. The pack voltage holds steady, so block 5 is still delivering its voltage to the series string; only the BMS's reading of it drops out. A reading that follows movement of the harness connector points to a loose or spread terminal on that block's sense lead.

   Why not the others

   A. Worn contacts would affect the voltage delivered past the contactor under load, not one block's reading inside the pack. The dropout follows the sense harness connector, so the sense lead terminal is at fault.

   B. An open inside block 5 would open the whole series string, and the pack voltage reading would change with it. The pack voltage holds steady, so the block is fine and the fault is in its sense lead.

   C. The current sensor measures pack current; it does not feed the block voltage readings, so it could not make one block's voltage drop out. The fault follows the sense harness connector.

   ID L3-A-021 · Task L3-A-5 (ASE task list)

2. Recall · Internal Combustion Engine

   A hybrid sits in the service bay in READY TO DRIVE with its engine stopped and the engine compartment silent. Why must it be switched OFF, with the smart key kept away as the manufacturer directs, before the technician reaches in near the drive belt or cooling fan?

   1. The engine block carries high voltage in this mode
   2. The DC/DC converter feeds high voltage to the fan
   3. The engine can start at any moment on its own
   4. The cooling fan runs at full speed in this mode
   Show the answer

   C. Correct. In READY TO DRIVE the system starts and stops the engine by itself, for battery charge, warm-up or other needs, so a silent engine can crank without warning and catch hands in the belt or fan. Switching OFF and keeping the smart key away prevents an accidental restart.

   Why not the others

   A. The HV system is isolated from the chassis and engine, so the block is never part of the HV circuit. The hazard in READY TO DRIVE is the engine starting without warning.

   B. The DC/DC converter steps high voltage down to supply the low-voltage system, so it does not feed high voltage to the fan or anything else. The reason to switch OFF is that the engine can start on its own.

   D. The fan runs on demand, not continuously at full speed. The real hazard is an engine that can start by itself while the vehicle is in READY TO DRIVE.

   ID L3-B-023 · Task L3-B-12 (ASE task list)

3. EXCEPT · Drive Systems

   A hybrid's isolation monitor has set a loss-of-isolation DTC, and the fault has been narrowed to one MG and its phase cables. Any of these could cause it EXCEPT:

   1. phase cable insulation chafed through on a bracket.
   2. an open circuit in one of the stator windings.
   3. stator winding insulation cracked by overheating.
   4. water that has entered a phase cable connector.
   Show the answer

   B. Correct. An open winding breaks the current path inside the MG, which upsets torque and sets a phase or current DTC, but it creates no path from the high-voltage circuit to the chassis. Loss of isolation needs a leak to ground, and the other three each provide one.

   Why not the others

   A. Chafed insulation lets a phase conductor touch or leak to the grounded bracket, which is exactly a loss of isolation. It could cause the DTC.

   C. Overheated, cracked winding insulation lets the copper leak to the stator core and the case. It could cause the DTC.

   D. Water in a connector forms a conductive path from the terminals to the grounded shell. It could cause the DTC.

   ID L3-C-018 · Task L3-C-6 (ASE task list)

4. Spec reading · Power Electronics

   A replacement inverter's HV input terminal nuts are specified at 13 N·m (115 in-lb). The torque wrench available for this range is scaled only in ft-lb. To what setting should it be adjusted?

   1. 9.6 ft-lb
   2. 11.5 ft-lb
   3. 13.0 ft-lb
   4. 17.6 ft-lb
   Show the answer

   A. Correct. There are 12 in-lb in 1 ft-lb, so 115 in-lb ÷ 12 = 9.6 ft-lb; the metric figure agrees, 13 N·m ÷ 1.356 = 9.6 ft-lb. HV terminal nuts are torqued exactly, because a loose joint heats under drive current and an overtightened one can crack the terminal or strip the stud.

   Why not the others

   B. That divides 115 in-lb by 10 instead of 12. A foot-pound is 12 inch-pounds, so the setting is 115 ÷ 12 = 9.6 ft-lb.

   C. That puts the N·m figure on a ft-lb scale without converting it. 13 N·m equals 9.6 ft-lb, since 1 ft-lb is about 1.356 N·m.

   D. That multiplies 13 N·m by 1.356 instead of dividing, converting the wrong way, and would overtighten the nut by more than 80 percent. The setting is 13 ÷ 1.356 = 9.6 ft-lb.

   ID L3-D-004 · Task L3-D-9 (ASE task list)

5. Recall · Supporting Systems

   On a mild 70°F day, a plug-in hybrid's energy information display shows the HV battery about one-fifth charged, yet the electric-only range reads 0 miles and the engine starts on the next drive. No warning lamps are on and no DTCs are stored. What does this mean?

   1. The state-of-charge reading has failed and needs testing
   2. A fault is keeping the vehicle out of electric-only mode
   3. The battery is too cold to supply electric-only driving
   4. The pack has reached the reserve kept for hybrid use
   Show the answer

   D. Correct. A plug-in hybrid drives on electricity until the pack reaches a floor it keeps in reserve, then runs as a regular hybrid, using that reserve for assist and regeneration. Electric-only range then reads 0 even though the pack still holds charge; plugging in restores it.

   Why not the others

   A. Nothing points to a bad reading: there is no DTC or warning, and a pack about one-fifth charged with 0 miles of electric range is how a plug-in hybrid normally looks once it reaches its hybrid reserve.

   B. A fault that kept the vehicle out of electric-only mode would be logged as a DTC, and none is stored. Electric-only range is 0 because the usable charge above the hybrid reserve is used up.

   C. On a 70°F day the pack is not cold enough to limit its output. The 0-mile range means the charge above the hybrid reserve has been used.

   ID L3-E-018 · Task L3-E-6 (ASE task list)

Want ten more with every option explained? Free L3 Light Duty Hybrid/Electric Vehicle Specialist questions: no account, no email, printable.