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Free Red Seal Automotive Service Technician (310S) Practice Test
30 original practice questions with explanations, written for the Red Seal Automotive Service Technician Interprovincial Exam. Pick an answer to check it instantly.
Last checked against Red Seal Program (with provincial and territorial apprenticeship authorities) on .
These are VoltExam questions, not official exam questions. Each shows the rule or standard to check it against. New to this exam? Read the Red Seal Automotive Service Technician (310S) guide.
Question 1 · A – Performs common occupational skills
You are about to raise a vehicle on a two-post hoist. After placing the lift arms, what should you do before raising it to working height?
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Answer: B. Confirm the pads are on the manufacturer's lift points, raise the wheels just off the floor and check the vehicle is stable
Lift pads must sit on the lift points shown in the service information, because other locations can slip or damage the body. Raising the vehicle a short distance and shaking it gently confirms it is balanced and secure before anyone works under it. Only then raise it to height and set the mechanical locks.
Check it: RSOS task A-1
Question 2 · A – Performs common occupational skills
On a metric 0–25 mm outside micrometer, the last fully visible line on the sleeve is 12.5 mm and thimble division 28 lines up with the sleeve's index line. What is the reading?
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Answer: D. 12.78 mm
A standard metric micrometer sleeve is graduated in 0.5 mm steps and each thimble division is 0.01 mm. Add the sleeve reading to the thimble reading: 12.5 mm + (28 × 0.01 mm) = 12.5 + 0.28 = 12.78 mm. 12.28 mm comes from ignoring the half-millimetre line on the sleeve.
Check it: RSOS task A-2
Question 3 · B – Engine and engine support systems
A dry compression test shows one cylinder well below the others. After adding a small amount of oil to that cylinder, its reading rises substantially. What is the most likely cause?
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Answer: A. Worn or damaged piston rings or cylinder wall
Oil temporarily seals the gap between the rings and the cylinder wall. If compression rises a lot on the wet test, the leak was past the rings. Valve and head gasket leaks are not sealed by oil, so their wet and dry readings stay about the same.
Check it: RSOS task B-4
Question 4 · B – Engine and engine support systems
During a cylinder leakage test with the piston at top dead centre on the compression stroke, you hear air escaping from the throttle body. Which component is most likely leaking?
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Answer: C. Intake valve
Where the air comes out shows where it is getting past. Air at the throttle body or intake means an intake valve is not sealing. Air at the tailpipe points to an exhaust valve, air at the oil fill or PCV points to rings, and bubbles in the coolant point to a head gasket or cracked head.
Check it: RSOS task B-4
Question 5 · B – Engine and engine support systems
A gasoline engine shows a large positive long-term fuel trim at idle that moves close to zero at higher engine speeds. Which fault best fits this pattern?
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Answer: C. An unmetered air (vacuum) leak
Positive fuel trim means the computer is adding fuel to correct a lean condition. Unmetered air from a vacuum leak is a large share of total airflow at idle but a small share at higher speeds, so the correction shrinks as rpm rises. A fuel delivery restriction usually gets worse under higher load, and a leaking injector causes rich (negative) trim.
Check it: RSOS task B-6
Question 6 · B – Engine and engine support systems
An upstream narrow-band zirconia oxygen sensor on a warm, running engine stays at about 0.1 V. What does this reading indicate?
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Answer: B. A lean mixture (excess oxygen in the exhaust), or a sensor or circuit fault
A zirconia sensor produces a high voltage (around 0.8–0.9 V) when the exhaust is low in oxygen (rich) and a low voltage (around 0.1 V) when the exhaust has excess oxygen (lean). A healthy sensor in closed loop switches back and forth; a reading stuck low means the engine is lean or the sensor or its circuit needs testing.
Check it: RSOS task B-6
Question 7 · B – Engine and engine support systems
On a diesel engine with selective catalytic reduction (SCR), what is the purpose of injecting diesel exhaust fluid (DEF) into the exhaust stream?
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Answer: D. To supply ammonia that the SCR catalyst uses to convert NOx into nitrogen and water
DEF is a urea and water solution. In the hot exhaust it breaks down into ammonia, which reacts with oxides of nitrogen over the SCR catalyst to form nitrogen and water vapour. Soot is removed by diesel particulate filter regeneration, and hydrocarbons and carbon monoxide are handled by the diesel oxidation catalyst.
Check it: RSOS task B-8
Question 8 · C – Vehicle module communications systems
With the battery disconnected, you measure resistance between CAN High and CAN Low at the data link connector of a high-speed CAN bus that uses two 120 Ω terminating resistors. What reading is normal?
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Answer: A. About 60 Ω
The two 120 Ω terminating resistors sit at the ends of the bus and are in parallel when measured between the two wires: 120 × 120 ÷ (120 + 120) = 60 Ω. A reading near 120 Ω suggests one terminator or one leg of the bus is open, and near 0 Ω suggests CAN High and CAN Low are shorted together.
Check it: RSOS task C-10
Question 9 · C – Vehicle module communications systems
On a high-speed CAN bus, what voltage would you expect on both CAN High and CAN Low when the bus is in the recessive (idle) state?
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Answer: C. About 2.5 V on both
In the recessive state both lines sit at about 2.5 V, so the difference between them is near zero. In the dominant state CAN High rises to about 3.5 V and CAN Low falls to about 1.5 V. Modules read the voltage difference, which is why the bus tolerates electrical noise that affects both wires equally.
Check it: RSOS task C-10
Question 10 · C – Vehicle module communications systems
Why should a stable power supply or battery maintainer be connected while programming a replacement control module?
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Answer: B. To keep system voltage steady, because a voltage drop during programming can interrupt the update and leave the module inoperative
Programming can take many minutes with the ignition on and modules awake, which draws the battery down. If voltage falls too low partway through, the write can fail and the module may be left unable to start or communicate. A stable supply keeps voltage within the range the programming procedure requires.
Check it: RSOS task C-11
Question 11 · D – Driveline systems
A differential's drive pinion has 10 teeth and its ring gear has 41 teeth. What is the final drive ratio?
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Answer: C. 4.10:1
Gear ratio = driven teeth ÷ driving teeth = 41 ÷ 10 = 4.10:1. The pinion turns 4.1 times for each turn of the ring gear, which multiplies torque and reduces speed. 0.24:1 comes from dividing the wrong way.
Check it: RSOS task D-12
Question 12 · D – Driveline systems
A front-wheel-drive vehicle makes a clicking or popping noise when accelerating through a sharp turn. What is the most likely cause?
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Answer: A. A worn outer constant velocity (CV) joint
The outer CV joint works at its largest angle when the wheels are turned sharply. Wear in the balls, cage or races then causes a rhythmic click under load. Inner joint wear more often shows up as a shudder or vibration during acceleration in a straight line.
Check it: RSOS task D-12
Question 13 · D – Driveline systems
Under which condition does a torque converter multiply engine torque?
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Answer: D. When there is a large speed difference between the impeller and turbine, such as accelerating from a stop
Torque multiplication happens when the turbine is much slower than the impeller. The stator, held by its one-way clutch, redirects fluid leaving the turbine so it helps push the impeller. As speeds equalize, the stator freewheels and the converter acts as a fluid coupling; with the converter clutch applied there is no multiplication at all.
Check it: RSOS task D-12
Question 14 · D – Driveline systems
When setting up a ring and pinion, what is the purpose of a gear tooth contact pattern check with marking compound?
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Answer: B. To confirm that pinion depth and backlash place tooth contact correctly on the ring gear teeth
Marking compound on the ring gear teeth shows where the pinion contacts them under load. The pattern's position on the drive and coast sides tells you whether pinion depth (shim) or backlash needs adjustment. An incorrect pattern leads to gear noise and early failure.
Check it: RSOS task D-13
Question 15 · E – Electrical and comfort control systems
Two 6 Ω lamps are connected in parallel across a 12 V supply. What is the total current drawn?
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Answer: D. 4 A
Two equal resistors in parallel give half the resistance of one: 6 ÷ 2 = 3 Ω. By Ohm's law, I = V ÷ R = 12 ÷ 3 = 4 A. Each lamp draws 2 A, and the currents add in a parallel circuit. 1 A is the answer for the same lamps in series (12 Ω).
Check it: RSOS task E-14
Question 16 · E – Electrical and comfort control systems
An engine cranks slowly even though the battery tests good. What is the best test to find excess resistance in the starter cables and connections?
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Answer: C. Perform voltage drop tests across each cable and connection while cranking
A voltage drop test is done with current flowing, so it reveals resistance from corrosion, loose terminals or damaged strands that an ohmmeter cannot see at the tiny current it uses. Measure across each section of the positive and ground paths while cranking and compare with the service information.
Check it: RSOS task E-14
Question 17 · E – Electrical and comfort control systems
When measuring parasitic battery draw with an ammeter in series at the battery, why do you wait before taking the reading?
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Answer: A. Many modules stay awake for a time after the ignition is off, so an early reading will be higher than the true resting draw
After key-off, modules keep running for a period to finish tasks, then enter sleep mode. Reading the draw before they sleep gives a misleadingly high value. Keep the meter connected so modules are not woken by breaking the circuit, and wait for them to go to sleep before reading.
Check it: RSOS task E-14
Question 18 · E – Electrical and comfort control systems
A fuse blows again as soon as a circuit is switched on. What is the correct next step?
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Answer: D. Find and repair the short to ground or overloaded component before installing a fuse of the specified rating
A fuse that blows immediately is doing its job: protecting the wiring from excessive current, usually caused by a short to ground. Fitting a larger fuse or bypassing it lets the wiring overheat and can start a fire. Locate the fault, repair it, then install the specified fuse.
Check it: RSOS task E-15
Question 19 · E – Electrical and comfort control systems
An A/C system cools poorly. With the engine running and A/C on, both the low-side and high-side pressures are lower than specified. What is the most likely cause?
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Answer: B. A low refrigerant charge
With too little refrigerant, the compressor has less to work with, so both sides read low and cooling suffers. Air in the system, an overcharge or a condenser that cannot shed heat all tend to push the high side higher than normal. Find and repair the leak before recharging to the specified amount.
Check it: RSOS task E-16
Question 20 · E – Electrical and comfort control systems
Why must R-134a and R-1234yf systems be serviced with separate, dedicated recovery and charging equipment?
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Answer: A. To prevent cross-contamination of the refrigerants and oils, and because R-1234yf is mildly flammable and needs equipment designed for it
Mixing refrigerants or their oils contaminates the system and the recovered refrigerant, hurting performance and making it unusable. The two systems use different service fittings to prevent mixing, and R-1234yf is classed as mildly flammable, so its equipment is built for that hazard.
Check it: RSOS task E-17
Question 21 · F – Steering, suspension, braking, tires, hubs and wheel bearings
A customer reports a spongy brake pedal that firms up when pumped. What is the most likely cause?
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Answer: C. Air in the hydraulic system
Air compresses while brake fluid does not, so air in the lines makes the pedal feel soft. Pumping moves more fluid in and temporarily takes up the slack. Glazed pads cause a hard pedal with poor stopping, and warped rotors cause pedal pulsation.
Check it: RSOS task F-18
Question 22 · F – Steering, suspension, braking, tires, hubs and wheel bearings
A tire shows excessive wear on both outer edges of the tread, with the centre less worn. What is the most likely cause?
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Answer: D. Underinflation
An underinflated tire sags in the middle, so the shoulders carry most of the load and wear fastest. Overinflation does the opposite and wears the centre. Camber problems wear one edge only, and toe problems cause a feathered wear pattern across the tread.
Check it: RSOS task F-18
Question 23 · F – Steering, suspension, braking, tires, hubs and wheel bearings
Running a hand across the front tire tread reveals a feathered (sawtooth) edge on each tread rib. Which alignment angle is most likely out of specification?
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Answer: B. Toe
Incorrect toe makes the tire scrub sideways as it rolls, which drags each tread rib and leaves a feathered edge. Toe is the alignment angle that wears tires fastest. Caster mainly affects steering effort, stability and pull, not tread wear.
Check it: RSOS task F-18
Question 24 · F – Steering, suspension, braking, tires, hubs and wheel bearings
What is the main effect of positive caster on a vehicle's steering?
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Answer: A. It improves directional stability and helps the steering wheel return to centre
Positive caster tilts the steering axis rearward at the top, so the tire's contact patch trails behind the steering axis like a shopping cart wheel. This gives straight-line stability and self-centring. More caster usually increases steering effort, and caster has little direct effect on tire wear.
Check it: RSOS task F-18
Question 25 · F – Steering, suspension, braking, tires, hubs and wheel bearings
Why do manufacturers call for glycol-based brake fluid (such as DOT 3 or DOT 4) to be replaced at intervals?
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Answer: B. It is hygroscopic: it absorbs moisture over time, which lowers its boiling point and promotes corrosion
Glycol-based brake fluids absorb water from the air through hoses and seals. Water lowers the fluid's boiling point, raising the risk of vapour lock and a fading pedal under hard braking, and it corrodes internal components. Flushing restores the fluid's properties.
Check it: RSOS task F-19
Question 26 · F – Steering, suspension, braking, tires, hubs and wheel bearings
What is the correct way to tighten wheel nuts when reinstalling a wheel?
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Answer: C. Snug them in a star (crisscross) pattern, then torque to specification with a torque wrench in the same pattern
A star pattern pulls the wheel evenly against the hub so it seats flat. Final tightening to the specified torque with a torque wrench prevents loose wheels from under-tightening and stretched studs or distorted rotors and drums from over-tightening.
Check it: RSOS task F-19
Question 27 · G – Restraint systems, body components, accessories and trim
Before replacing a steering column component near the driver's airbag, what should you do after turning the ignition off?
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Answer: D. Disconnect the battery and wait the time specified in the service information before disconnecting any restraint components
The restraint control module has a reserve energy capacitor that can still fire an airbag for a time after power is removed. Disconnecting the battery and waiting the manufacturer's specified time lets that energy dissipate. Follow the service procedure for disabling the system before unplugging or handling any inflator.
Check it: RSOS task G-21
Question 28 · G – Restraint systems, body components, accessories and trim
Why should you never test an airbag inflator (squib) circuit by connecting a test light or ohmmeter directly to the inflator?
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Answer: A. The tester's current could ignite the inflator and deploy the airbag
Inflators are fired by a small electrical current, and the current a test light or meter supplies could be enough to cause deployment. Service procedures use the restraint system's own diagnostics, scan tool data and approved load tools that substitute for the inflator during testing.
Check it: RSOS task G-20
Question 29 · H – Hybrid and electric vehicle (EV) systems
After removing the high-voltage service disconnect on a hybrid vehicle, what must you do before touching high-voltage components?
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Answer: B. Wait the specified time, then verify absence of voltage with a properly rated meter while wearing inspected, rated insulating gloves
Capacitors in the inverter can stay charged after the disconnect is removed, so you must wait the time specified by the manufacturer. Then confirm zero voltage at the high-voltage terminals with a meter rated for the system, wearing insulating gloves that have been inspected for damage. Never assume the system is dead.
Check it: RSOS task H-23
Question 30 · H – Hybrid and electric vehicle (EV) systems
What colour is the insulation used to identify high-voltage cables on hybrid and electric vehicles?
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Answer: C. Orange
Orange is the industry convention for high-voltage cables and conduits on hybrid and electric vehicles. It warns technicians and first responders that the circuit can carry dangerous voltage. Treat any orange cable as live until it has been verified de-energized.
Check it: RSOS task H-22
Official sources
- Red Seal – Automotive Service Technician trade page ↗
- Red Seal – Automotive Service Technician exam information (breakdown) ↗
- Red Seal – Automotive Service Technician occupational standard ↗
- Red Seal – Overview of the Red Seal Examination ↗
- Red Seal – Automotive Service Technician exam self-assessment guide (PDF) ↗
- Skilled Trades Ontario – Automotive Service Technician (310S) ↗
- Saskatchewan Apprenticeship – Automotive Service Technician exam information 2026 (PDF) ↗
Sources checked November 2, 2026. VoltExam is independent and not affiliated with Red Seal Program (with provincial and territorial apprenticeship authorities). Rules change: confirm details with the official source before your exam.