310T Hybrid and Electric Vehicles

Question 1

Before working on the high-voltage system of a hybrid truck, a technician must de-energize the system. What is the FIRST step after donning appropriate PPE?

Accepted Answer

Remove the high-voltage service disconnect (manual service disconnect) plug

Answer

Disconnect the 12 V auxiliary battery negative cable

Answer

Cut the orange high-voltage cables to isolate the circuit

Answer

Discharge the HV capacitors using a load resistor connected to the DC bus

Question 2

Which color is universally used on hybrid and electric trucks to identify high-voltage cables and components?

Accepted Answer

Orange

Answer

Red

Answer

Yellow

Answer

Blue

Question 3

What is regenerative braking in a hybrid truck, and what is its primary benefit?

Accepted Answer

A system where the electric motor acts as a generator during deceleration, converting kinetic energy back into electrical energy stored in the battery

Answer

An air brake enhancement that uses compressed air to slow the vehicle and store energy in an air tank

Answer

An exhaust brake system that redirects exhaust gases to charge a turbocharger while decelerating

Answer

A hydraulic accumulator system that stores braking energy as pressurized fluid

Question 4

A hybrid truck's high-voltage battery management system (BMS) triggers a fault and limits power output. Which parameter does the BMS monitor to protect the battery pack?

Accepted Answer

Cell voltage, state of charge (SOC), and cell temperature

Answer

Engine coolant temperature and oil pressure

Answer

Transmission fluid temperature and gear position

Answer

12 V auxiliary battery voltage and alternator output

Question 5

A technician measures 450 V DC between the positive and negative HV bus terminals after removing the manual service disconnect. What should the technician do?

Accepted Answer

Immediately reinstall the MSD and consult the OEM service manual before continuing

Answer

Proceed with repairs — the disconnect was already removed so the voltage will discharge on its own

Answer

Short the two bus terminals together through a 10-ohm resistor to force rapid discharge

Answer

Cover the terminals with electrical tape and complete the repair quickly to minimize exposure

Question 6

When performing routine maintenance on an electric transit coach, a technician notices the high-voltage interlock loop (HVIL) circuit has opened. What does this indicate?

Accepted Answer

A high-voltage connector or cover is not fully seated, triggering a safety shutdown

Answer

The HV battery is fully charged and has disconnected to prevent overcharge

Answer

The regenerative braking system has detected excessive heat and disabled itself

Answer

The 12 V auxiliary battery has failed and disconnected the control system