ASE Practice Test (L2: Light Duty Hybrid/Electric Vehicle) 3

Question 1

What type of battery chemistry is most commonly used in modern hybrid and electric vehicle HV battery packs?

Accepted Answer

Lithium-ion (Li-ion) in various chemistries (NMC, LFP, NCA)

Answer

Lithium-ion batteries dominate modern HV hybrid and EV applications due to their high energy density, low self-discharge rate, no memory effect, and long cycle life. Different lithium chemistries are used: NMC (Nickel Manganese Cobalt) for high energy density, LFP (Lithium Iron Phosphate) for safety and longevity, NCA (Nickel Cobalt Aluminum) for high performance. Earlier hybrids used NiMH (Nickel Metal Hydride), which is less energy-dense but more robust.

Question 2

How do brake pads typically wear differently on a hybrid or electric vehicle compared to a conventional vehicle?

Accepted Answer

Hybrid/EV pads last significantly longer because regenerative braking reduces reliance on friction brakes, but this can cause pad and rotor surface degradation from lack of use and corrosion

Answer

Because regenerative braking handles most low-to-moderate deceleration in hybrids and EVs, friction brakes are applied far less frequently. This means brake pads and rotors last much longer than in conventional vehicles. However, infrequent friction brake use allows brake rotors to develop surface rust and glazing (especially in humid climates), which can cause brake noise, pulsation, and reduced stopping performance when hard braking is finally needed. Regular inspection for rotor condition is essential even when pads appear thick.

Question 3

What is the function of the DC-DC converter in a hybrid or electric vehicle?

Accepted Answer

Convert high-voltage DC from the HV battery to 12-14V DC to power conventional 12V vehicle systems and charge the auxiliary battery

Answer

Unlike conventional vehicles that use an alternator to charge the 12V battery and power accessories, hybrids and EVs use a DC-DC converter. This device steps the HV battery voltage (200-800V) down to approximately 13-14V DC to power all conventional 12V vehicle systems (lighting, radio, BCM, etc.) and keep the 12V auxiliary battery charged. If the DC-DC converter fails, the 12V system will discharge and the vehicle will lose normal electrical function.

Question 4

An EV has reduced maximum range. All battery cells test within specification for voltage, and no DTCs are present. What should the technician measure next?

Accepted Answer

Battery capacity (amp-hour or kWh capacity) using a battery capacity test, and compare to new-battery specification to quantify capacity degradation

Answer

Battery cell voltage at rest (open-circuit voltage) does not reveal capacity loss — a cell can hold correct voltage but have reduced energy storage capacity due to lithium depletion and electrode degradation over years of cycling. A battery capacity test charges the battery fully, then discharges it under a controlled load while measuring total energy delivered. Comparing this to the new-battery rated capacity quantifies the degradation. Typical EV batteries retain 80% capacity after 8-10 years.

Question 5

When a plug-in hybrid electric vehicle (PHEV) is connected to a Level 2 (240V AC) charging station, what component in the vehicle converts the AC charging current to DC for battery storage?

Accepted Answer

The on-board charger (OBC)

Answer

The on-board charger (OBC) is a vehicle-mounted AC-to-DC power converter that accepts AC power from the charging station (Level 1: 120V, Level 2: 240V) and converts it to the correct DC voltage and current for charging the HV battery. The OBC includes rectification, power factor correction, and voltage regulation. DC Fast Charging (Level 3) bypasses the OBC and delivers DC directly to the battery through a separate high-power inlet (CHAdeMO, CCS, or NACS).