Five free practice questions on trailers and reefer units: block H of the Red Seal 310T Truck and Coach Technician exam, about 8 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
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A driver reports the trailer's lights work only intermittently and the ABS lamp flickers. The tractor works fine with other trailers. Where should the technician look on the trailer?
- The landing gear gearbox.
- The trailer's tires and wheel ends.
- The kingpin and upper coupler.
- The nose-box socket and grounds.
Show the answer
D. Correct. When the tractor is fine on other trailers, the fault is in the trailer's electrical system: the seven-pin socket in the nose box, its wiring, splices and especially the ground connections, which corrode from road salt and produce exactly this intermittent behaviour across several circuits. The RSOS lists malfunctioning lights among trailer symptoms and corrosion and loose fasteners among faults; the technician inspects and cleans the socket pins, checks voltage drop on the ground under load, and repairs the harness with sealed connections.
Why not the others
A. Landing gear is unrelated to the lighting circuits.
B. Tires have no role in the lighting or ABS circuits.
C. The kingpin is mechanical and carries no electrical circuit.
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A refrigerated trailer's unit fails to start on a cold morning; it cranks slowly and stops. The technician load-tests the unit's battery and it fails. What is the correct next step, and why?
- Replace the battery and release the trailer.
- Add starting fluid to the intake.
- Test the charging system first.
- Replace the refrigerant.
Show the answer
C. Correct. A failed battery may be the victim of a charging fault: the RSOS requires the starting and charging systems to be tested for voltage and amperage draw according to the manufacturer's information, and lists corroded electrical connectors, broken or loose belts and frayed or chafed wires among faults. If the unit's alternator, belt or connections are not charging, a new battery will fail the same way. The battery is replaced and the charging output, belt and connections confirmed; the fuel system is also checked for water and gelling in cold weather.
Why not the others
A. Replacing the battery without testing the charging system risks a repeat failure.
B. Ether on a unit that may have an intake heater is dangerous, and it does not fix a battery or charging fault.
D. Refrigerant has nothing to do with the engine starting.
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A technician must repair a cracked upper coupler (kingpin plate) on a trailer. What governs how the repair is done?
- Filling the crack with sealant.
- Bolting a plate over the crack.
- Whatever weld the shop can do quickly.
- OEM procedure and certified welding.
Show the answer
D. Correct. The upper coupler carries the trailer's vertical load and all drawbar and braking forces; a cracked plate is a critical safety defect. The RSOS lists king pins, hitches and couplers among trailer components replaced and repaired according to the manufacturer's information and requires the technician to identify the codes, standards and regulations pertaining to trailer components; coupler repairs and kingpin replacement are done to the manufacturer's engineered procedure by a certified welder, and the trailer stays out of service until completed and inspected.
Why not the others
A. Sealant has no structural value.
B. A cover plate does not restore the coupler's strength and is not an approved repair.
C. An uncertified, unengineered weld on a coupler is a trailer-separation risk.
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While inspecting a reefer unit's fuel system, the technician finds the fuel line rubbing on a frame bracket with the outer cover worn through, and a tank strap missing. What should be done?
- Nothing; the tank is held by the other strap.
- Tighten the remaining strap harder.
- Clamp the line properly; replace the strap.
- Wrap the line in tape and move on.
Show the answer
C. Correct. The RSOS requires fuel lines to be secured using fasteners (insulated clamps, separators) to prevent chafing or kinking, and lists loose, worn or missing tank straps, cracked mounting brackets and broken fasteners among the wear and damage to identify on fuel system mounting hardware. A chafed line leaks diesel onto a hot unit, a listed fuel-spill hazard; a missing strap lets the tank move and stress its fittings. The damaged line section is replaced, the run secured clear of the bracket with insulated clamps, and the strap and any cracked bracket replaced.
Why not the others
A. A tank with a missing strap is a listed defect; the strap is replaced.
B. Over-tightening one strap distorts the tank and does not replace the missing support.
D. Tape wears through again; the line is secured and, where damaged, replaced.
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A trailer is reported to be difficult to couple and the tractor's fifth wheel will not lock cleanly on it, though the fifth wheel works on other trailers. What should the technician inspect on the trailer?
- The trailer's ABS module and lamp.
- The kingpin and upper plate.
- The rear swing doors and hinges.
- The landing gear and crank.
Show the answer
B. Correct. When the same fifth wheel couples other trailers correctly, the trailer's kingpin or upper coupler plate is the variable: a bent kingpin (from a hard hook-up or a drop) or a worn one will not centre in the jaws or lets the lock close loosely, and a warped or cracked upper plate holds the pin at the wrong angle or height. The RSOS lists bent or worn king pins among symptoms and king pins among components; the pin is checked with a wear gauge and a straight edge and the plate inspected for cracks and welds, and the pin or plate is replaced by a certified repair per the manufacturer.
Why not the others
A. The ABS has no role in mechanical coupling.
C. Doors are unrelated to the kingpin coupling.
D. Landing gear height affects coupling ease but not whether the lock closes on the pin.
02Answer key
| Question | Answer | Sub-task |
|---|---|---|
| Q1 | D | Diagnoses trailer components and accessories |
| Q2 | C | Diagnoses heating and refrigeration systems |
| Q3 | D | Repairs trailer components and accessories |
| Q4 | C | Services heating and refrigeration systems |
| Q5 | B | Diagnoses trailer components and accessories |
03What block H covers
This block covers trailers and the units that keep their cargo cold or warm. It includes landing gear, sliding bogies and lift axles, kingpins and upper couplers, lights, conspicuity tape and the nose-box socket, van bodies, doors, floors and riveted panels, and diesel-powered reefer units with electric standby, refrigerant leaks and propane-fired heaters.
The Red Seal Occupational Standard names this block “Services, diagnoses and repairs trailers”. It carries 5.9% of the exam, about 8 of the 135 questions, split across two tasks. The share column is each task's weight within the block, as the standard publishes it.
| Task and its sub-tasks | Share of block |
|---|---|
| Services, diagnoses and repairs trailer components and accessories Services trailer components and accessories; Diagnoses trailer components and accessories; Repairs trailer components and accessories | 59% |
| Services, diagnoses and repairs heating and refrigeration systems Services heating and refrigeration systems; Diagnoses heating and refrigeration systems; Repairs heating and refrigeration systems | 41% |
04What the questions turn on
Sliding bogie locking pins
A sliding tandem is held in place only by its locking pins. Pins that cannot seat in worn, elongated rail holes can release under braking and let the axles slide, so the trailer stays out of service until rails and pins are repaired.
Coupling trouble on the trailer side
If the tractor's fifth wheel locks cleanly on other trailers, look at this trailer's kingpin and upper plate for bending, wear or cracks. A cracked upper coupler is repaired only to the manufacturer's procedure by a certified welder.
Flickering trailer lights and ABS
When the tractor works with other trailers, the fault is on the trailer, most often the nose-box socket and its ground connections corroded by road salt. Clean the socket pins and voltage-drop test the ground under load.
Reefer no-start in the cold
A reefer battery that fails a load test may be the victim of a charging fault, so test the alternator, belt and connections before trusting a new battery. Cleaned starter, alternator and battery connections get dielectric grease to keep moisture out.
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.