Free Red Seal Truck and Transport Mechanic (310T) Practice Test

Answer: C. Lower the load onto rated jack stands under solid points and chock the wheels on the ground

A jack is a lifting device, not a support device; hydraulic seals can leak down without warning. Lower the load onto stands rated for the weight, placed under solid frame or axle points, and chock the wheels still on the floor so the vehicle cannot roll.

Check it: RSOS task A-1

Answer: A. Set to its lowest scale setting (not below it) and kept in its case

Leaving a click-type wrench under spring tension for long periods lets the spring take a set, so the wrench clicks early or late. Backing it off to the lowest marked setting, without unwinding past it, relieves the spring while keeping the mechanism engaged. It should still be calibrated on schedule.

Check it: RSOS task A-2

Answer: B. Non-combustible ash has built up and must be cleaned out or the filter replaced

Regeneration burns off soot, but the ash left from lube oil additives cannot burn. As ash accumulates it takes up filter volume, so the pressure differential rises sooner and regenerations become more frequent. The fix is removing the DPF for off-vehicle ash cleaning or replacing it, then looking for the source of high oil consumption.

Check it: RSOS task B-8

Answer: D. 32.5% urea

DEF is 32.5% high-purity urea in deionized water. That ratio gives the lowest freezing point of the mixture and the concentration the SCR dosing system is calibrated for. Diluted or contaminated fluid causes quality faults, poor NOx conversion and possible engine derate.

Check it: RSOS task B-8

Answer: A. Coolant entering the oil, such as from an oil cooler or liner seal leak

Glycol is an antifreeze component, and sodium and potassium come from coolant additives, so together they point to coolant contamination of the oil. Common sources are oil coolers, wet liner seals, cylinder head gaskets and EGR coolers on some designs. Coolant in oil destroys lubrication, so the leak must be found and fixed before the next oil change.

Check it: RSOS task B-6

Answer: C. It opens the exhaust valves near TDC compression, venting the compressed air

With fuelling cut, the engine still uses power to compress the intake charge. A compression-release brake opens the exhaust valve near top dead centre, venting that compressed air, so the energy is not given back on the power stroke. The engine becomes an air compressor that absorbs vehicle momentum. An exhaust brake, by contrast, uses a valve in the exhaust to create back pressure.

Check it: RSOS task B-11

Answer: B. Air trapped in the fuel system because it was not properly primed

Opening the filters lets air into the low-pressure side. The high-pressure pump cannot build rail pressure while it is pumping air, so the ECM will not fire the injectors. Prime the system with the hand or electric primer as the service information directs and confirm fuel supply and rail pressure with a scan tool before chasing other faults.

Check it: RSOS task B-10

Answer: D. The air compressor is passing excess oil into the discharge

Oil in the air system comes from the compressor, which is lubricated by engine oil. Worn rings, high crankcase pressure, a restricted compressor intake or excessive duty cycle can push oil past into the discharge. An oil-soaked dryer cartridge cannot remove moisture, so replace it after correcting the compressor problem and check downstream valves for contamination.

Check it: RSOS task C-13

Answer: A. 1.7 kN·m

First find pushrod force: F = P × A = 620 000 Pa × 0.0194 m² ≈ 12 028 N (about 12.0 kN). Torque on the camshaft is force times the slack adjuster length: 12 028 N × 0.140 m ≈ 1684 N·m, or about 1.7 kN·m. A longer slack adjuster arm or larger chamber gives more brake torque at the same pressure.

Check it: RSOS task C-14

Answer: D. Close off tractor air to the trailer while the trailer spring brakes apply

When supply line pressure falls, the tractor protection valve closes to stop the tractor losing its own air through the broken line, and the trailer control valve pops out. With no supply pressure, the trailer's spring brakes apply automatically. The tractor keeps enough air in its own reservoirs to stop under control.

Check it: RSOS task C-13

Answer: B. Find out why the adjuster is not holding adjustment, and repair the cause

Automatic slack adjusters should hold stroke within limits on their own. If one is out of adjustment, manually adjusting it only hides the problem. Look for worn cam bushings, seized components, worn linings or drums, incorrect installation or a failed adjuster, and repair the cause before returning the vehicle to service.

Check it: RSOS task C-14

Answer: C. About 60 Ω

A J1939 backbone has a 120 Ω terminating resistor at each end. In parallel they measure about 60 Ω. A reading near 120 Ω means one terminator or one side of the backbone is open, and a reading near 0 Ω means the two wires are shorted together.

Check it: RSOS task D-20

Answer: A. 0.6 V

Using Ohm's law, V = I × R = 400 A × 0.0015 Ω = 0.6 V. Even a tiny resistance causes a large drop at cranking current, which is why corroded or undersized cables cause slow cranking. Compare the measured drop with the manufacturer's limit for the circuit.

Check it: RSOS task D-18

Answer: B. 12 V and 3800 CCA

In parallel, positives connect to positives and negatives to negatives, so voltage stays at 12 V while current capacity adds: 4 × 950 = 3800 CCA. Connecting batteries in series would add voltages instead. All batteries in a parallel pack should be the same type and similar age and state of charge.

Check it: RSOS task D-15

Answer: D. Voltage below normal or shorted to a low source

In J1939, the SPN identifies what failed and the FMI describes how. FMI 4 means voltage below normal or shorted low, such as a signal wire shorted to ground or an open supply. FMI 3 is the opposite, voltage above normal or shorted high. Knowing the FMI tells you which circuit tests to do first.

Check it: RSOS task D-20

Answer: A. Excessive resistance in the charging output circuit

A voltage drop test on the charging output side measures resistance in the cable, connections and any fuse link while current flows. A drop of over a volt is far too high; it means the batteries see much less voltage than the alternator produces. Clean, tighten or replace connections and cables, then retest.

Check it: RSOS task D-16

Answer: C. 3.73:1

Gear ratio = driven teeth ÷ driving teeth = 41 ÷ 11 ≈ 3.73:1. The pinion turns 3.73 times for each turn of the ring gear and wheels. Using a hunting tooth combination like 41/11 spreads wear evenly because the same teeth do not mesh on every revolution.

Check it: RSOS task E-26

Answer: A. Engaging the lock while wheels were spinning shock-loaded the gears

The interaxle differential lock should be engaged while the wheels are not spinning, at low speed with light throttle. Engaging it while one axle is spinning suddenly forces both axles to turn together, which can break the sliding clutch, shafts or gears. It must also be released on good traction to avoid driveline wind-up and tire wear.

Check it: RSOS task E-26

Answer: B. The universal joints are out of phase

In a two-joint driveshaft, the yokes at each end must be in phase (in line) so the speed fluctuations from the first joint are cancelled by the second. Assembling the slip yoke off its alignment marks puts the joints out of phase, causing a vibration tied to driveshaft speed. Reassemble using the alignment marks and check working angles.

Check it: RSOS task E-25

Answer: C. To stop the input shaft so a starting gear can be engaged when stopped

The clutch brake is applied at the very end of clutch pedal travel and squeezes against the release bearing to stop the input shaft spinning. That lets the driver engage a starting gear without grinding. It is not meant for use while moving; doing so for upshifts wears it out rapidly.

Check it: RSOS task E-21

Answer: D. No gap at the upper coupler, and the jaws locked around the kingpin shank

A tug test shows the trailer is held, but you must also look: the trailer upper plate should sit flat on the fifth wheel with no gap, the jaws must be closed around the shank of the kingpin rather than its head, and the release handle must be in the locked position. A high hitch can let the kingpin sit on top of the jaws.

Check it: RSOS task F-31

Answer: B. In a star pattern, in stages, to the specified torque, then rechecked later

A star pattern pulls the wheel down evenly against the hub face, centring it on the pilots. Tightening in stages prevents distortion, and a final torque wrench check ensures the specified clamp load. Joints can settle in the first period of operation, so re-torque as the manufacturer recommends.

Check it: RSOS task F-32

Answer: C. Height control valve linkage adjustment and ride height setting

The height control (leveling) valve fills or exhausts the air springs to hold a set ride height, using a linkage to the axle. A bent, disconnected or misadjusted linkage makes the valve read the wrong height and exhaust or fill constantly. Set ride height to specification using the service procedure, then confirm the valve centres and stops flowing air.

Check it: RSOS task F-30

Answer: A. Excessive toe-in

Toe-in that is too high scrubs both front tires across the road, typically leaving feathered wear starting on the outer edges. Toe is the most common steer-tire wear adjustment and should be set after checking for worn tie rod ends. Drive axle misalignment can also cause steer tire wear, so check tandem alignment as well.

Check it: RSOS task F-28

Answer: B. An air leak at the seat air spring, fittings or height control valve

An air-ride seat holds its height with a small air spring controlled by a valve. If it fills but then slowly sinks, air is escaping from the spring, its lines and fittings, or a leaking control valve. Soap-test the components with the seat raised to find the leak, then repair or replace the faulty part.

Check it: RSOS task G-33

Answer: D. That all locking pins are fully engaged through the body rail holes

The locking pins hold the slider sub-frame to the trailer body rails. If any pin is not fully through its hole, the slider can shift under braking or acceleration, damaging the trailer and creating a serious hazard. Check each pin visually after the move and confirm the pin release handle is locked.

Check it: RSOS task H-35

Answer: C. To melt frost from the evaporator coil so airflow and heat transfer are restored

Moisture from the cargo space freezes on the cold evaporator coil. As frost builds up, it blocks airflow and insulates the coil, cutting refrigeration capacity. A defrost cycle, often using hot gas or electric heat, melts the frost and drains it away, after which normal cooling resumes.

Check it: RSOS task H-36

Answer: D. Poor heat rejection at the condenser due to reduced airflow

The condenser must give up heat to outside air to change the refrigerant back to liquid. Blocked fins reduce airflow, so condensing pressure and temperature rise, and the low side rises with it. Clean the condenser and check fan operation before considering charge problems. A restriction or low charge would give a low suction reading instead.

Check it: RSOS task I-38

Answer: C. 85.5 kN

Area of an 80 mm bore = π × (0.040 m)² ≈ 0.005027 m². Force = pressure × area = 17 000 000 Pa × 0.005027 m² ≈ 85 450 N, or about 85.5 kN. Using the diameter instead of the radius in the area formula would give a force four times too large (342 kN).

Check it: RSOS task J-39

Answer: B. HV-to-chassis resistance has dropped, so there may be a leakage path

High-voltage systems are isolated from the chassis. An isolation monitor measures resistance between the HV circuits and ground; when it drops below a threshold, there may be a leakage path that could shock someone touching the vehicle. Treat the vehicle as hazardous, follow the de-energizing procedure and use rated PPE and meters to find the fault.

Check it: RSOS task K-41