Cert III Automotive Mechanic cheat sheet

Hierarchy of control, highest to lowest: eliminate the hazard, substitute, engineer controls, administrative controls, PPE.

SDS sections: 1 identification, 2 hazard identification, 3 composition, 4 first aid, 5 firefighting, 6 spill response, 7 handling and storage, 8 exposure controls, 9 physical properties.

Australian workplace exposure standard for respirable crystalline silica is 0.05 mg/m3 as an 8-hour time-weighted average; crystalline silica is a confirmed carcinogen.

Carbon monoxide binds haemoglobin roughly 200-250 times more strongly than oxygen; never run engines in an enclosed workshop without extraction.

Refrigerant R134a is a fluorinated greenhouse gas with global warming potential of 1430; recovery is mandatory before opening an air-conditioning circuit.

A class B fire involves flammable liquids; a CO2 or dry chemical extinguisher is suitable, water is not because it spreads burning fuel.

Manual handling rule of thumb: keep the load close to the body, bend the knees, and avoid twisting while lifting; team-lift loads above about 20 kg.

Used oil, filters, batteries and solvent rags are tracked wastes and must go to licensed recyclers, not general refuse.

Torque wrench accuracy is typically plus or minus 4 percent of setting; recalibrate annually and after any drop or over-range use.

Micrometer reading equals barrel value plus thimble value; a 0-25 mm metric micrometer thimble has 50 divisions, each 0.01 mm.

Vernier caliper resolution is main scale division divided by number of vernier divisions, commonly 0.02 mm.

Feeler gauge blades must slide with slight drag; a blade that will not enter or enters freely indicates the gap is outside the selected size.

Tap drill size for a metric coarse thread is nominal diameter minus pitch, for example M8 x 1.25 uses a 6.75 mm drill.

Bolt grade markings: metric class 8.8 and 10.9 indicate tensile strength in hundreds of MPa; imperial grade 5 and grade 8 use radial line marks.

Hydraulic press and puller use requires eye protection and a shield; never apply heat to a pressurised or sealed component.

Left-hand thread fasteners are identified by notches on the hex head or an L marking; turning clockwise loosens them.

Four-stroke order: intake, compression, power, exhaust; a full cycle takes two crankshaft revolutions and one camshaft revolution.

Engine displacement equals bore area times stroke times number of cylinders; bore area is pi times radius squared.

Compression ratio equals swept volume plus clearance volume, divided by clearance volume.

A cylinder leakage test above about 20 percent indicates a sealing fault; air from the dipstick points to rings, from the intake to inlet valve, from the exhaust to exhaust valve.

Valve clearance is measured cold on most engines with a feeler gauge between cam lobe base circle and follower.

Timing belt replacement intervals are typically 90,000-120,000 km or 5-7 years; a broken belt on an interference engine causes valve-to-piston contact.

Blue exhaust smoke indicates oil burning, black smoke indicates rich mixture, white persistent smoke indicates coolant entering combustion.

Cylinder head bolt torque-to-yield fasteners are single-use and must be replaced and tightened in the specified sequence and angle.

Ohm's law: voltage equals current times resistance; power in watts equals volts times amps.

Series circuit: resistances add, current is common, voltages divide. Parallel circuit: voltage is common, currents add, total resistance is less than the smallest branch.

A 12 V battery at rest should read about 12.6 V fully charged, 12.2 V at 50 percent, and below 12.0 V is discharged; charging voltage is 13.8-14.7 V.

Voltage drop testing is done under load; a drop above 0.5 V on a high-current circuit indicates excessive resistance.

Parasitic drain above about 50 mA after modules sleep indicates a fault; measure with a clamp meter to avoid waking the network.

Controller area network uses twisted pair wiring with 120 ohm terminating resistors; normal bus resistance is about 60 ohms.

Alternator output test: at 2000 rpm with loads on, output should be within about 10 percent of rated current and ripple under 0.5 V AC.

High-voltage systems on hybrid and electric vehicles are orange-coded; isolation testing requires a category III rated meter and qualified personnel.

Hydraulic pressure equals force divided by piston area; a larger master cylinder bore increases fluid volume but reduces line pressure for a given pedal force.

Brake fluid is hygroscopic; DOT 4 has a minimum dry boiling point of 230 C and wet boiling point of 155 C, and is typically replaced every 2 years.

Minimum friction material thickness is commonly 2 mm for pads and 1 mm above the rivet for riveted linings; discard below specification.

Brake rotor minimum thickness is stamped on the rotor; machining must leave it above that value, and runout above about 0.05 mm can cause pedal pulsation.

Pedal sinks slowly under steady pressure: internal master cylinder bypass or external leak. Pedal is spongy: air in the hydraulic circuit.

Drum brake self-energising effect means leading shoe wears faster; automatic adjusters must be set so shoes lightly contact the drum before assembly.

ABS warning lamp staying on after bulb check disables ABS but leaves base braking; scan for wheel speed sensor codes and check tone rings.

Parking brake cable free play is typically adjusted so the lever reaches the specified number of clicks with wheels locked.

Wheel alignment angles: camber is vertical tilt viewed from front, caster is steering axis tilt viewed from side, toe is the difference in distance between front and rear of the wheels.

Positive camber tilts the top of the wheel outward; excessive negative camber wears the inner tyre edge.

Incorrect toe is the most common cause of rapid, feathered tyre wear; toe-in means fronts of wheels are closer than rears.

Caster provides self-centring and straight-line stability; too little caster causes wander, too much increases steering effort.

Tyre placard pressure is cold pressure; pressure rises about 1 psi per 5.5 C of temperature increase.

Tread wear indicator bars sit at 1.6 mm; tyres below the legal minimum are unroadworthy.

MacPherson strut combines the damper and spring into one unit and provides the upper steering pivot; it must be realigned after replacement.

Power steering diagnosis: whine that increases on full lock suggests low fluid or air ingress; stiff steering with a good pump points to a seized ball joint or column.

Manual gear ratio equals driven gear teeth divided by drive gear teeth; overall ratio is gearbox ratio times final drive ratio.

A clutch should have about 20-25 mm of pedal free play; no free play causes release bearing wear and slipping.

Clutch slip shows as rising engine speed without road speed increase; judder points to contaminated or warped friction surfaces.

Automatic transmission fluid level is checked with the engine running in park or neutral at operating temperature per the manufacturer's procedure; overfilling causes aeration.

Automatic transmission fluid that is dark or burnt-smelling indicates overheated clutches; manufacturer-specific fluid is required because friction modifiers differ.

Constant velocity joint clicking on full lock indicates a worn outer joint; vibration under acceleration suggests an inner joint or driveshaft imbalance.

Differential backlash and tooth contact pattern must be checked with marking compound after any crown wheel and pinion change.

Limited slip differentials may require a friction modifier additive; omitting it causes chatter on tight turns.

Coolant mixture is typically 50/50 ethylene glycol and water, giving freeze protection near -37 C and a boiling point above 125 C under pressure.

A 15 psi radiator cap raises boiling point by roughly 3 C per psi, about 45 C above the unpressurised boiling point.

Thermostat opening temperature is stamped on the housing; a stuck-open thermostat causes slow warm-up and poor heater output.

Oil viscosity grade such as 5W-30: the first number is cold-flow rating, the second is kinematic viscosity at 100 C; follow the manufacturer's specification.

Oil pressure warning at idle with correct level suggests worn bearings or a faulty pressure relief valve; verify with a mechanical gauge.

Fuel trims: short-term and long-term fuel trim beyond plus or minus 10 percent indicates a mixture or metering fault.

Fuel pressure specification is measured with the pump running and regulator connected; low pressure causes lean running and hard starting.

Cooling system pressure test: hold specified pressure for the manufacturer's time; a falling gauge indicates an external or internal leak.

Three-way catalytic converter reduces hydrocarbons and carbon monoxide by oxidation and nitrogen oxides by reduction; it needs closed-loop stoichiometric operation.

Positive crankcase ventilation routes blow-by gases to the intake; a blocked PCV valve causes oil leaks and rough idle.

Exhaust gas recirculation lowers combustion temperature to reduce nitrogen oxides; a stuck-open valve causes rough idle and stalling.

Evaporative emission systems store fuel vapour in a charcoal canister; a faulty purge valve or leaking cap sets a small leak code.

Oxygen sensor output should switch rapidly between about 0.1 V and 0.9 V; a lazy sensor causes poor fuel economy.

Roadworthy inspection items include tyre tread, brake performance, lights, steering play, suspension, seat belts, windscreen, and structural rust.

On-board diagnostics mode 6 displays non-continuous monitor test results; readiness monitors must be complete before a scan is accepted.

Visible black smoke from a diesel indicates over-fuelling; excessive particulate matter can breach emission standards and fail inspection.

A repair order must record customer details, vehicle identification number, odometer, complaint in the customer's words, and authorisation for work.

Written authorisation is required before exceeding an agreed quote; verbal approval should be documented with time, name, and scope.

Vehicle identification number is 17 characters and encodes manufacturer, attributes, and a check digit; it is used to confirm parts fitment.

Consumer law requires services be performed with due care and skill and be fit for purpose; guarantees cannot be excluded by contract.

Personal information collected for repairs is governed by privacy law: collect only what is needed, store securely, and do not disclose without consent.

Warranty on parts and labour must be stated on the invoice, including the period and conditions.

Technician licensing, refrigerant handling, and waste transport are regulated by state and territory authorities; keep certificates current.

Records of servicing, torque values used, and parts fitted must be retained so a repair can be audited or defended later.

Hierarchy of control, highest to lowest: eliminate the hazard, substitute, engineer controls, administrative controls, PPE.

SDS sections: 1 identification, 2 hazard identification, 3 composition, 4 first aid, 5 firefighting, 6 spill response, 7 handling and storage, 8 exposure controls, 9 physical properties.

Australian workplace exposure standard for respirable crystalline silica is 0.05 mg/m3 as an 8-hour time-weighted average; crystalline silica is a confirmed carcinogen.

Carbon monoxide binds haemoglobin roughly 200-250 times more strongly than oxygen; never run engines in an enclosed workshop without extraction.

Refrigerant R134a is a fluorinated greenhouse gas with global warming potential of 1430; recovery is mandatory before opening an air-conditioning circuit.

A class B fire involves flammable liquids; a CO2 or dry chemical extinguisher is suitable, water is not because it spreads burning fuel.

Manual handling rule of thumb: keep the load close to the body, bend the knees, and avoid twisting while lifting; team-lift loads above about 20 kg.

Used oil, filters, batteries and solvent rags are tracked wastes and must go to licensed recyclers, not general refuse.

Torque wrench accuracy is typically plus or minus 4 percent of setting; recalibrate annually and after any drop or over-range use.

Micrometer reading equals barrel value plus thimble value; a 0-25 mm metric micrometer thimble has 50 divisions, each 0.01 mm.

Vernier caliper resolution is main scale division divided by number of vernier divisions, commonly 0.02 mm.

Feeler gauge blades must slide with slight drag; a blade that will not enter or enters freely indicates the gap is outside the selected size.

Tap drill size for a metric coarse thread is nominal diameter minus pitch, for example M8 x 1.25 uses a 6.75 mm drill.

Bolt grade markings: metric class 8.8 and 10.9 indicate tensile strength in hundreds of MPa; imperial grade 5 and grade 8 use radial line marks.

Hydraulic press and puller use requires eye protection and a shield; never apply heat to a pressurised or sealed component.

Left-hand thread fasteners are identified by notches on the hex head or an L marking; turning clockwise loosens them.

Four-stroke order: intake, compression, power, exhaust; a full cycle takes two crankshaft revolutions and one camshaft revolution.

Engine displacement equals bore area times stroke times number of cylinders; bore area is pi times radius squared.

Compression ratio equals swept volume plus clearance volume, divided by clearance volume.

A cylinder leakage test above about 20 percent indicates a sealing fault; air from the dipstick points to rings, from the intake to inlet valve, from the exhaust to exhaust valve.

Valve clearance is measured cold on most engines with a feeler gauge between cam lobe base circle and follower.

Timing belt replacement intervals are typically 90,000-120,000 km or 5-7 years; a broken belt on an interference engine causes valve-to-piston contact.

Blue exhaust smoke indicates oil burning, black smoke indicates rich mixture, white persistent smoke indicates coolant entering combustion.

Cylinder head bolt torque-to-yield fasteners are single-use and must be replaced and tightened in the specified sequence and angle.

Ohm's law: voltage equals current times resistance; power in watts equals volts times amps.

Series circuit: resistances add, current is common, voltages divide. Parallel circuit: voltage is common, currents add, total resistance is less than the smallest branch.

A 12 V battery at rest should read about 12.6 V fully charged, 12.2 V at 50 percent, and below 12.0 V is discharged; charging voltage is 13.8-14.7 V.

Voltage drop testing is done under load; a drop above 0.5 V on a high-current circuit indicates excessive resistance.

Parasitic drain above about 50 mA after modules sleep indicates a fault; measure with a clamp meter to avoid waking the network.

Controller area network uses twisted pair wiring with 120 ohm terminating resistors; normal bus resistance is about 60 ohms.

Alternator output test: at 2000 rpm with loads on, output should be within about 10 percent of rated current and ripple under 0.5 V AC.

High-voltage systems on hybrid and electric vehicles are orange-coded; isolation testing requires a category III rated meter and qualified personnel.

Hydraulic pressure equals force divided by piston area; a larger master cylinder bore increases fluid volume but reduces line pressure for a given pedal force.

Brake fluid is hygroscopic; DOT 4 has a minimum dry boiling point of 230 C and wet boiling point of 155 C, and is typically replaced every 2 years.

Minimum friction material thickness is commonly 2 mm for pads and 1 mm above the rivet for riveted linings; discard below specification.

Brake rotor minimum thickness is stamped on the rotor; machining must leave it above that value, and runout above about 0.05 mm can cause pedal pulsation.

Pedal sinks slowly under steady pressure: internal master cylinder bypass or external leak. Pedal is spongy: air in the hydraulic circuit.

Drum brake self-energising effect means leading shoe wears faster; automatic adjusters must be set so shoes lightly contact the drum before assembly.

ABS warning lamp staying on after bulb check disables ABS but leaves base braking; scan for wheel speed sensor codes and check tone rings.

Parking brake cable free play is typically adjusted so the lever reaches the specified number of clicks with wheels locked.

Wheel alignment angles: camber is vertical tilt viewed from front, caster is steering axis tilt viewed from side, toe is the difference in distance between front and rear of the wheels.

Positive camber tilts the top of the wheel outward; excessive negative camber wears the inner tyre edge.

Incorrect toe is the most common cause of rapid, feathered tyre wear; toe-in means fronts of wheels are closer than rears.

Caster provides self-centring and straight-line stability; too little caster causes wander, too much increases steering effort.

Tyre placard pressure is cold pressure; pressure rises about 1 psi per 5.5 C of temperature increase.

Tread wear indicator bars sit at 1.6 mm; tyres below the legal minimum are unroadworthy.

MacPherson strut combines the damper and spring into one unit and provides the upper steering pivot; it must be realigned after replacement.

Power steering diagnosis: whine that increases on full lock suggests low fluid or air ingress; stiff steering with a good pump points to a seized ball joint or column.

Manual gear ratio equals driven gear teeth divided by drive gear teeth; overall ratio is gearbox ratio times final drive ratio.

A clutch should have about 20-25 mm of pedal free play; no free play causes release bearing wear and slipping.

Clutch slip shows as rising engine speed without road speed increase; judder points to contaminated or warped friction surfaces.

Automatic transmission fluid level is checked with the engine running in park or neutral at operating temperature per the manufacturer's procedure; overfilling causes aeration.

Automatic transmission fluid that is dark or burnt-smelling indicates overheated clutches; manufacturer-specific fluid is required because friction modifiers differ.

Constant velocity joint clicking on full lock indicates a worn outer joint; vibration under acceleration suggests an inner joint or driveshaft imbalance.

Differential backlash and tooth contact pattern must be checked with marking compound after any crown wheel and pinion change.

Limited slip differentials may require a friction modifier additive; omitting it causes chatter on tight turns.

Coolant mixture is typically 50/50 ethylene glycol and water, giving freeze protection near -37 C and a boiling point above 125 C under pressure.

A 15 psi radiator cap raises boiling point by roughly 3 C per psi, about 45 C above the unpressurised boiling point.

Thermostat opening temperature is stamped on the housing; a stuck-open thermostat causes slow warm-up and poor heater output.

Oil viscosity grade such as 5W-30: the first number is cold-flow rating, the second is kinematic viscosity at 100 C; follow the manufacturer's specification.

Oil pressure warning at idle with correct level suggests worn bearings or a faulty pressure relief valve; verify with a mechanical gauge.

Fuel trims: short-term and long-term fuel trim beyond plus or minus 10 percent indicates a mixture or metering fault.

Fuel pressure specification is measured with the pump running and regulator connected; low pressure causes lean running and hard starting.

Cooling system pressure test: hold specified pressure for the manufacturer's time; a falling gauge indicates an external or internal leak.

Three-way catalytic converter reduces hydrocarbons and carbon monoxide by oxidation and nitrogen oxides by reduction; it needs closed-loop stoichiometric operation.

Positive crankcase ventilation routes blow-by gases to the intake; a blocked PCV valve causes oil leaks and rough idle.

Exhaust gas recirculation lowers combustion temperature to reduce nitrogen oxides; a stuck-open valve causes rough idle and stalling.

Evaporative emission systems store fuel vapour in a charcoal canister; a faulty purge valve or leaking cap sets a small leak code.

Oxygen sensor output should switch rapidly between about 0.1 V and 0.9 V; a lazy sensor causes poor fuel economy.

Roadworthy inspection items include tyre tread, brake performance, lights, steering play, suspension, seat belts, windscreen, and structural rust.

On-board diagnostics mode 6 displays non-continuous monitor test results; readiness monitors must be complete before a scan is accepted.

Visible black smoke from a diesel indicates over-fuelling; excessive particulate matter can breach emission standards and fail inspection.

A repair order must record customer details, vehicle identification number, odometer, complaint in the customer's words, and authorisation for work.

Written authorisation is required before exceeding an agreed quote; verbal approval should be documented with time, name, and scope.

Vehicle identification number is 17 characters and encodes manufacturer, attributes, and a check digit; it is used to confirm parts fitment.

Consumer law requires services be performed with due care and skill and be fit for purpose; guarantees cannot be excluded by contract.

Personal information collected for repairs is governed by privacy law: collect only what is needed, store securely, and do not disclose without consent.

Warranty on parts and labour must be stated on the invoice, including the period and conditions.

Technician licensing, refrigerant handling, and waste transport are regulated by state and territory authorities; keep certificates current.

Records of servicing, torque values used, and parts fitted must be retained so a repair can be audited or defended later.