SOLAS Heavy Vehicle Mechanic common mistakes
SOLAS Heavy Vehicle Mechanic · Understand the traps and how to avoid them.
Diagnosing a starting fault by naming a single component (e.g. 'the starter is gone') before checking battery state of charge, voltage drop across the earth strap, and cranking current draw.
Candidates memorise component names from workshop experience and jump to the part they have replaced before; the exam asks for the diagnostic sequence and evidence, so a single-part answer loses the reasoning marks.
What to do instead
Practise writing a fixed diagnostic order for every no-crank or slow-crank scenario: battery open-circuit voltage and load test, terminal and earth voltage drop under cranking, starter solenoid control circuit, then starter current draw. State the measured value that would confirm or exclude each step before moving on.
Reading a wiring diagram as a physical layout and then answering questions about circuit protection or control-side switching from the wrong side of the load.
Many candidates learn wiring from vehicle harnesses they can see, so they trace by position rather than by current path; exam questions deliberately redraw the circuit in schematic form with the switch on the earth side.
What to do instead
Redraw every circuit as a current path from supply through protection, switch, load and back to earth, and mark which side of the load the switch sits on. Practise identifying control-side switching, relay coil versus contact circuits, and where a short to earth would blow the fuse.
Quoting torque figures or fastener sequences from memory without stating the unit, the thread condition (dry, oiled, thread-locking compound) or the tightening pattern.
In the workshop the torque wrench is preset and the manual is open; under exam conditions candidates recall only the number and omit the conditions that make the number valid.
What to do instead
Build a revision table pairing each critical fastener (cylinder head, main bearing cap, wheel nut, injector clamp) with its torque, angular stage, lubrication state and sequence. In answers always state unit (N·m), thread condition and whether the value is a stage in a torque-to-yield procedure.
Treating brake fault diagnosis as pad replacement, and failing to separate hydraulic, mechanical and electronic causes when answering questions on poor braking, pull or drag.
Routine servicing dominates apprenticeship experience, so candidates default to friction material; the exam tests systematic isolation of a fault across the whole system including ABS and load-sensing valves.
What to do instead
For each brake symptom, write three columns (hydraulic, mechanical, electronic) and list at least two checks per column with the expected reading. Include runout measurement, calliper slide condition, brake fluid moisture content, and ABS fault-code retrieval as routine steps.
Ignoring the legal and record-keeping dimension of heavy vehicle work, such as who may certify a repair, what a roadworthiness inspection covers, and what must be recorded after a safety-related repair.
Apprentices learn the physical task from a mentor who handles the paperwork, so the compliance side is never practised and questions on inspection intervals or certification are answered from guesswork.
What to do instead
Make a one-page summary of the inspection and certification regime that applies to the vehicles you work on: who is authorised, what intervals apply, which items are safety-critical, and what documentation must be completed and retained. Test yourself by writing the record entry for a completed steering repair.
Answering diesel fuel system questions by describing the injector only, without linking low-pressure supply, filtration, air ingress and return flow to the high-pressure fault.
Common-rail injectors are the visible, expensive part and dominate discussion in the workshop, so candidates skip the supply side even though most poor-running complaints originate there.
What to do instead
Learn the fuel system as three stages (tank and lift pump, filtration and low-pressure regulation, high-pressure pump, rail and injectors) and for each symptom state one low-pressure and one high-pressure test with the acceptance value. Practise interpreting rail pressure actual versus desired and injector return-flow results.
Describing cooling system faults only as 'radiator blocked' or 'thermostat stuck', without addressing coolant specification, pressure testing, aeration and fan or viscous coupling operation.
Overheating is a frequent workshop job with a familiar answer, so candidates give the common fix rather than the test procedure; exam items probe the sequence and the chemistry of coolant.
What to do instead
Write a cooling system test routine: cold pressure test and hold time, cap relief pressure check, coolant concentration and type verification, thermostat opening check in heated water, and fan drive engagement test. Match each fault symptom to the test that confirms it.
Calculating gear ratios, road speed or engine speed with the wrong units, or forgetting to convert tyre diameter to circumference before applying the formula.
Candidates rely on a phone calculator and a remembered formula, so unit conversion and the distinction between radius and diameter are lost under exam pressure.
What to do instead
Rehearse a single written method: tyre circumference from diameter in metres, then road speed equals engine speed divided by overall ratio, multiplied by circumference, with a units line written at every step. Do five worked examples including a two-speed final drive and a direct-drive top gear.
Naming a transmission or driveline fault without separating clutch, gearbox, propshaft and final drive contributions, and without interpreting the conditions under which the noise or vibration occurs.
Driveline faults sound similar and candidates answer from the last similar job they saw rather than from a symptom-to-cause matrix keyed to speed, load and gear.
What to do instead
Build a matrix with rows for speed-dependent, load-dependent and gear-specific symptoms and columns for clutch, gearbox, propshaft, differential and wheel end. For each cell write the confirming test, such as propshaft runout, universal joint play, or oil condition and magnet check.
Neglecting safe working practices as an exam topic, answering a repair question without stating isolation of stored energy, support of the vehicle, or handling of high-pressure and high-voltage systems.
Safety is habitual in the workshop and therefore invisible to the candidate, but the exam awards marks for stating the control measures explicitly, especially on hybrid and high-pressure fuel systems.
What to do instead
For each major job, write the isolation and support steps before the repair steps: chock and support points, battery or high-voltage isolation and proving dead, depressurisation of fuel and air systems, and PPE. Practise adding a two-line safety statement to every practical answer.