310T hybrid and electric vehicles practice questions.

Four free practice questions on hybrid and electric vehicles: block K of the Red Seal 310T Truck and Coach Technician exam, about 4 of its 135 questions. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. Critical · Diagnoses hybrid vehicles

   A parallel hybrid coach descends a 12 km (7.5 mi) mountain grade and arrives with its friction brakes smoking, and the driver reports the regenerative braking 'did nothing'. No fault codes are stored, the HV battery is at 32 °C (90 °F), and the data log shows the HV battery at 96 % SOC at the top of the grade after 40 km (25 mi) of highway cruising. What explains the complaint?

   1. Wheel-speed sensor fault inhibiting regen
   2. Brake blending controller fault
   3. HV battery over-temperature limiting charge
   4. Regen was limited by the battery's high SOC
   Show the answer

   D. Correct. Regenerative braking charges the HV battery; at 96 % SOC there is almost nowhere for the energy to go, so the controller limits regen and blends in friction braking for the whole descent, which cooks the brakes. This is design behaviour, not a fault: the driver must use the engine or exhaust brake and gear selection on long grades. Explain it to the driver and inspect the friction brakes for heat damage.

   Why not the others

   A. A wheel-speed fault would log an ABS code and light the ABS lamp; the log shows no codes. Regen was inhibited by the battery's state, not by the brake control inputs.

   B. A blending fault would set a code and usually a brake warning; with no codes stored and the friction brakes clearly working, the shift to friction was commanded, not a malfunction.

   C. 32 °C is a normal pack temperature; a thermal derate would appear well above that and would log a warning. The limiting factor recorded was the 96 % SOC, not temperature.

2. Critical · Diagnoses electric vehicles (EV)

   An electric truck has reduced power and an HV battery temperature warning, and the technician finds a coolant leak at the battery pack's cooling manifold. What is the concern and the required approach?

   1. Top up the coolant and release the truck.
   2. Drive it to see if it gets worse.
   3. Disconnect the battery temperature sensor.
   4. Overheating risk; lock out, repair, test.
   Show the answer

   D. Correct. The pack is liquid-cooled; a leak lets the cells overheat, which the module answers by limiting power, and coolant inside the pack can create an isolation fault between HV and chassis. The RSOS lists lack of power and indicator lights among symptoms, leaks among defects, insulation and voltage isolation among tests, and high working temperatures among hazards. The HV system is deactivated and locked out, the leak repaired per the manufacturer, the pack checked for coolant intrusion, the cooling system refilled and bled, and an insulation test performed before re-energizing.

   Why not the others

   A. The leak and the possible isolation fault remain; the pack could overheat or fault on the road.

   B. An overheating HV battery is a fire risk; the vehicle is repaired first.

   C. Removing the warning removes the protection, not the problem.

3. Critical · Diagnoses electric vehicles (EV)

   A battery-electric straight truck will not enter READY each morning until its 12 V AGM battery is boosted; it then runs all day. Live data with the truck in READY: DC-DC converter output 14.1 V at the 12 V battery, HV battery 82 % SOC. After an overnight sit the 12 V battery reads 11.2 V and the key-off draw measures 30 mA against a 50 mA limit. What is the fault?

   1. DC-DC converter output too low
   2. Excessive key-off draw
   3. HV battery contactor failing to close
   4. The 12 V battery cannot hold a charge
   Show the answer

   D. Correct. The DC-DC converter is the only 12 V charging source and it is delivering 14.1 V; the key-off draw is within limit; yet the battery falls to 11.2 V overnight, so it has lost capacity (sulphated or a failed cell). On an EV the 12 V battery must power the control modules before the HV contactors can close, which is why a weak 12 V battery presents as 'no READY'. Conductance or load test it and replace.

   Why not the others

   A. 14.1 V at the 12 V battery in READY is a normal converter output; the battery is being charged correctly all day and losing it overnight.

   B. 30 mA is inside the 50 mA limit, so nothing is discharging the battery abnormally. A battery that goes from 14.1 V charging to 11.2 V with only 30 mA flowing has lost capacity.

   C. READY works every time once the 12 V side is boosted, and the HV pack is at 82 % SOC; the contactors close as soon as the low-voltage system can power the control modules.

4. Critical · Diagnoses electric vehicles (EV)

   An electric bus will not charge at the depot's plug-in charger, though it drives normally and other buses charge at the same charger. What should the technician check on the bus?

   1. Charge port and on-board charger.
   2. The windshield washer system.
   3. The tire pressures on every axle.
   4. The brake linings and drums.
   Show the answer

   A. Correct. When the charger works on other buses, the fault is on the vehicle: the charge port's contacts and interlock (which must confirm a locked connector before charging is enabled), the on-board charger or its HV contactors, and the communication between the charger and the vehicle's module. The RSOS lists charging systems among EV components and components not functioning among symptoms, and requires codes to be retrieved and tests performed per the manufacturer; the charging devices and HV system are locked out before the port and charger wiring are inspected and tested.

   Why not the others

   B. Washers are unrelated.

   C. Tires have nothing to do with charging.

   D. Brakes are unrelated to charging.

02Answer key

03What block K covers

This block covers hybrid and battery-electric trucks and buses. It includes series, parallel and series/parallel hybrid layouts, HV batteries, inverters, drive motors and converters, lock-out and zero-voltage verification, insulation and isolation testing, plug-in, fast charge and overhead charging systems, battery pack cooling, and the PPE and meters that high-voltage work requires.

The Red Seal Occupational Standard names this block “Services, diagnoses and repairs hybrid and electric vehicles (EV)”. It carries 3% of the exam, about 4 of the 135 questions, split across two tasks. The share column is each task's weight within the block, as the standard publishes it.

04What the questions turn on

Lock out, then verify zero

Turn the key off, disconnect the 12 V battery, remove and lock out the HV service disconnect, and wait the discharge time. Then verify zero voltage at the HV terminals with a CAT-rated meter while wearing rated insulating gloves.

Chasing an isolation fault

An isolation fault means high voltage is leaking to the chassis. With the system locked out, an insulation tester checks each HV circuit to chassis against the manufacturer's minimum, and the circuit is split until the low reading is found.

Coolant leaks at the pack

A battery cooling leak lets the cells overheat, so the module limits power, and coolant inside the pack can cause an isolation fault. After the repair, check the pack for coolant intrusion and insulation-test before re-energizing.

A bus that will not charge

If other buses charge at the same charger, the fault is on the vehicle: the charge port contacts and interlock, the on-board charger or its contactors, or communication between the charger and the vehicle's module.

05The other blocks

The 310T exam has 11 blocks. Each has its own page of free questions:

The 310T Truck and Coach Technician practice exam 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.