Odisha CHSE VOC-ITV Four Wheeler Service Technician cheat sheet
Odisha CHSE VOC-ITV Four Wheeler Service Technician · Keep the key ideas within reach.
Workshop safety, tools and equipment
Torque is force times perpendicular distance: T (N·m) = F (N) × r (m); 1 kgf·m = 9.81 N·m.
Outside micrometer least count is 0.01 mm (thimble has 50 divisions; one full turn advances the spindle 0.50 mm); vernier caliper least count is 0.02 mm.
Dial gauge or DTI least count is 0.01 mm; it is used for shaft runout, brake disc runout and gear backlash.
Torque wrench accuracy is typically ±4%; recalibrate annually and after any drop or overload, checking at 20%, 60% and 100% of scale.
Jack stands must be rated for at least 1.5 times the supported load; never place any body part under a vehicle held only by a hydraulic jack.
Fire classes: A solids, B flammable liquids, C flammable gases, D metals; use CO2 or dry powder on fuel and electrical fires, never water.
Plastigauge measures bearing oil clearance by crush width; feeler gauge measures valve clearance and piston ring end gap.
Compressed air for cleaning must be below 2 bar and fitted with a safety nozzle; never direct air at skin.
Petrol exhaust contains carbon monoxide; run engines only with hose extraction, and maintain workshop ventilation of at least 10 air changes per hour.
Engine construction, operation and overhaul
Four-stroke cycle: intake, compression, power and exhaust; the crankshaft turns 720° per cycle while the camshaft turns 360°.
Displacement = (π/4) × bore² × stroke × number of cylinders.
Compression ratio = (swept volume + clearance volume) ÷ clearance volume.
Inline four-cylinder firing orders are 1-3-4-2 or 1-2-4-3; inline six-cylinder firing order is 1-5-3-6-2-4.
Valve clearance is set cold; typical intake 0.15–0.25 mm and exhaust 0.20–0.35 mm, unless the manufacturer specifies hot adjustment.
Cylinder bore taper and out-of-round are generally limited to 0.05 mm; measure at top, middle and bottom in two directions.
Piston ring end gap rule of thumb is 0.003–0.004 × bore in mm for the top ring; file-fit rings must be checked in the bore.
Torque-to-yield head bolts are tightened to a torque plus a specified angle and must be replaced, not reused.
Main bearing oil clearance is typically 0.03–0.08 mm; measure with plastigauge across the full bearing width.
Fuel supply, injection and emission control systems
Stoichiometric petrol air-fuel ratio is 14.7:1 by mass; diesel stoichiometric ratio is about 14.5:1.
Lambda λ = actual AFR ÷ stoichiometric AFR; λ = 1.00 is chemically correct, λ > 1 is lean and λ < 1 is rich.
Port fuel injection pressure is 2.5–4 bar; gasoline direct injection is 50–200 bar; common-rail diesel is 200–2,000 bar.
Three-way catalyst oxidises CO and HC and reduces NOx; it needs closed-loop lambda control oscillating near 1.00.
EGR lowers NOx by diluting the charge and reducing peak combustion temperature; typical rate is 5–20%.
DPF active regeneration burns soot at 550–650°C; frequent short journeys prevent passive regeneration and can block the filter.
Fuel trim: positive trim means the ECU adds fuel for a lean condition; long-term trim beyond ±25% usually sets a fault code.
OBD-II powertrain codes start with P; P0171 is lean bank 1 and P0300 is random or multiple-cylinder misfire.
PCV and EVAP systems control crankcase blow-by and fuel vapour; a stuck-open purge valve causes rough idle and lean codes.
Cooling and lubrication systems
A 50:50 ethylene glycol/water coolant mix gives freeze protection near −37°C and boil protection near 108°C at atmospheric pressure.
A 1 bar (about 15 psi) pressure cap raises the coolant boiling point by roughly 25°C, to about 125°C.
Thermostat begins to open at 82–90°C and is fully open at 95–100°C; a stuck-open thermostat causes slow warm-up and weak heater output.
Coolant circulation path: water pump → engine block → cylinder head → radiator → thermostat → water pump.
Oil grade 5W-30: 5W is the cold-flow rating and 30 is the high-temperature viscosity; a lower W number gives better cold cranking.
Hot idle oil pressure is typically 1.5–4.5 bar; below about 0.5 bar the warning lamp comes on and the engine must be stopped.
The oil filter bypass valve opens when the element is clogged or the oil is cold, protecting flow at the cost of filtration.
Coolant pH should be 7.5–11.0; a hydrometer or refractometer measures freeze point, not condition alone.
Clutch, transmission, propeller shaft and differential
Clutch pedal free play is 10–20 mm; excess free play causes incomplete disengagement, while too little causes release bearing drag.
Clutch disc rivet depth minimum is about 0.3 mm above the friction lining; worn lining or oil contamination causes slip or judder.
Final drive ratio = ring gear teeth ÷ pinion teeth; a numerically higher ratio increases torque and reduces top speed.
Propeller shaft universal joint yokes must be in phase; working angles should be equal and opposite and generally below 3°.
Hypoid differential backlash is typically 0.15–0.25 mm; set pinion preload and backlash before final torque.
Manual gearbox synchronisers use cone friction; a worn blocker ring causes gear clash, especially on downshift.
Automatic transmission fluid level is checked with the engine running, transmission hot, in Park or Neutral as specified.
A split CV joint boot allows grease loss and grit entry; clicking noise on full lock indicates outer CV joint wear.
Limited-slip differentials require a friction modifier; without it, chattering occurs on tight turns.
Steering, suspension, wheels and tyres
Ackermann geometry: the inner wheel steers a larger angle than the outer wheel; toe-out on turns is normal and non-adjustable.
Positive caster improves straight-line stability and self-centring but increases steering effort; typical value is 2–8°.
Camber is wheel vertical tilt; negative camber improves cornering grip but increases inner-edge tyre wear.
Toe-in is the difference between front and rear distances across the wheels; typical total toe is 0–3 mm for passenger cars.
Tyre size 205/55 R16 means 205 mm section width, 55% aspect ratio, radial construction and a 16-inch rim.
Cold tyre pressure changes about 1 psi per 10°F (5.6°C) ambient change; set pressures when tyres are cold.
Wheel radial runout limit is typically 1.5 mm and lateral runout 1.0 mm; balance with static and dynamic correction.
Legal minimum tread depth is 1.6 mm across the central three-quarters; replace earlier for wet braking.
MacPherson strut combines spring, damper and upper pivot; a worn top mount causes knocking and changes camber.
Braking systems
Hydraulic brake force multiplication: F2 = F1 × (A2 ÷ A1); Pascal's law transmits pressure equally through the fluid.
DOT 3 dry boiling point is at least 205°C and DOT 4 at least 230°C; glycol fluids absorb moisture and should be replaced about every two years.
Brake fluid moisture above 3% lowers boiling point and risks vapour lock; test with an electronic moisture tester.
Disc brake rotor runout limit is typically 0.05 mm; minimum friction pad thickness is about 2 mm.
Bleeding sequence farthest from the master cylinder first: right rear, left rear, right front, left front.
ABS operates at roughly 5–15 cycles per second and needs wheel speed signals; a failed sensor disables ABS.
The drum brake leading shoe is self-energising; incorrect shoe placement causes unequal braking or grab.
Parking brake cable travel and rear shoe adjustment affect handbrake effectiveness; check on a slope.
Automotive electrical and electronic systems
Ohm's law: V = I × R; power P = V × I = I²R.
A 12 V lead-acid battery has six cells at about 2.1 V each; specific gravity is 1.265 when full and 1.120 when discharged.
Alternator charging voltage is 13.8–14.4 V; AC ripple above 0.5 V indicates diode failure.
Starter current draw is typically 150–250 A; cranking voltage should stay above about 9.6 V at 20°C.
High-speed CAN uses 500 kbit/s and two 120 Ω terminating resistors, giving about 60 Ω across CAN-H and CAN-L.
LIN bus runs at 19.2 kbit/s as a single-wire sub-bus for sensors and actuators.
NTC thermistor resistance falls as temperature rises; it is used for coolant and intake air temperature sensors.
Voltage drop across a good connection should be below 0.1 V at full load; test with a voltmeter while current flows.
ECU 5 V reference supplies sensors; a shorted reference pulls down all sensors on that circuit.
Vehicle diagnosis and troubleshooting
DTC P0171 means fuel system lean bank 1; causes include vacuum leak, dirty MAF, weak fuel pump or leaking injector.
Positive fuel trim means the ECU is adding fuel because the mixture is lean; negative trim means it is reducing fuel because the mixture is rich.
Compression test: hold throttle open, disable ignition and injection, crank evenly; cylinders should be within 10% of each other.
Vacuum gauge at idle should read 17–22 inHg steady; a fluctuating needle suggests valve leakage, sticking or a vacuum leak.
P0300 means random or multiple-cylinder misfire; isolate with cylinder balance or misfire counter data.
No-start diagnosis follows air, fuel, spark and compression; confirm cranking speed and battery voltage first.
Parasitic draw: key-off current is normally below 50 mA; measure with an ammeter in series after modules sleep.
Freeze-frame data records engine conditions when a DTC set; use it to reproduce the fault.
Oscilloscope checks injector and ignition waveforms for burn time, peak voltage and dwell.
Periodic servicing, vehicle inspection and workshop management
Oil change interval is commonly 5,000–10,000 km; severe duty such as short trips, dust or towing uses the shorter interval.
Air filter 15,000–30,000 km; brake fluid 2 years; coolant 2–5 years depending on type.
PDI checks include fluid levels, tyre pressures, battery, lights, road test and removal of transport protection.
Waste oil is hazardous waste: store in labelled closed containers and give it to an authorised recycler; never mix with solvents.
Refrigerant must be recovered, not vented; use a recovery machine and record the amount.
5S means sort, set in order, shine, standardise and sustain; it supports tool control and workshop safety.
Job card should record customer complaint, VIN, mileage, parts, labour and technician sign-off.
Lift safety: check rated capacity, position pads at manufacturer lift points, and lock mechanical safeties before working underneath.
Emission inspection: petrol engines are measured for CO and HC at idle and fast idle; diesel is measured for smoke opacity.
Workshop safety, tools and equipment
Torque is force times perpendicular distance: T (N·m) = F (N) × r (m); 1 kgf·m = 9.81 N·m.
Outside micrometer least count is 0.01 mm (thimble has 50 divisions; one full turn advances the spindle 0.50 mm); vernier caliper least count is 0.02 mm.
Dial gauge or DTI least count is 0.01 mm; it is used for shaft runout, brake disc runout and gear backlash.
Torque wrench accuracy is typically ±4%; recalibrate annually and after any drop or overload, checking at 20%, 60% and 100% of scale.
Jack stands must be rated for at least 1.5 times the supported load; never place any body part under a vehicle held only by a hydraulic jack.
Fire classes: A solids, B flammable liquids, C flammable gases, D metals; use CO2 or dry powder on fuel and electrical fires, never water.
Plastigauge measures bearing oil clearance by crush width; feeler gauge measures valve clearance and piston ring end gap.
Compressed air for cleaning must be below 2 bar and fitted with a safety nozzle; never direct air at skin.
Petrol exhaust contains carbon monoxide; run engines only with hose extraction, and maintain workshop ventilation of at least 10 air changes per hour.
Engine construction, operation and overhaul
Four-stroke cycle: intake, compression, power and exhaust; the crankshaft turns 720° per cycle while the camshaft turns 360°.
Displacement = (π/4) × bore² × stroke × number of cylinders.
Compression ratio = (swept volume + clearance volume) ÷ clearance volume.
Inline four-cylinder firing orders are 1-3-4-2 or 1-2-4-3; inline six-cylinder firing order is 1-5-3-6-2-4.
Valve clearance is set cold; typical intake 0.15–0.25 mm and exhaust 0.20–0.35 mm, unless the manufacturer specifies hot adjustment.
Cylinder bore taper and out-of-round are generally limited to 0.05 mm; measure at top, middle and bottom in two directions.
Piston ring end gap rule of thumb is 0.003–0.004 × bore in mm for the top ring; file-fit rings must be checked in the bore.
Torque-to-yield head bolts are tightened to a torque plus a specified angle and must be replaced, not reused.
Main bearing oil clearance is typically 0.03–0.08 mm; measure with plastigauge across the full bearing width.
Fuel supply, injection and emission control systems
Stoichiometric petrol air-fuel ratio is 14.7:1 by mass; diesel stoichiometric ratio is about 14.5:1.
Lambda λ = actual AFR ÷ stoichiometric AFR; λ = 1.00 is chemically correct, λ > 1 is lean and λ < 1 is rich.
Port fuel injection pressure is 2.5–4 bar; gasoline direct injection is 50–200 bar; common-rail diesel is 200–2,000 bar.
Three-way catalyst oxidises CO and HC and reduces NOx; it needs closed-loop lambda control oscillating near 1.00.
EGR lowers NOx by diluting the charge and reducing peak combustion temperature; typical rate is 5–20%.
DPF active regeneration burns soot at 550–650°C; frequent short journeys prevent passive regeneration and can block the filter.
Fuel trim: positive trim means the ECU adds fuel for a lean condition; long-term trim beyond ±25% usually sets a fault code.
OBD-II powertrain codes start with P; P0171 is lean bank 1 and P0300 is random or multiple-cylinder misfire.
PCV and EVAP systems control crankcase blow-by and fuel vapour; a stuck-open purge valve causes rough idle and lean codes.
Cooling and lubrication systems
A 50:50 ethylene glycol/water coolant mix gives freeze protection near −37°C and boil protection near 108°C at atmospheric pressure.
A 1 bar (about 15 psi) pressure cap raises the coolant boiling point by roughly 25°C, to about 125°C.
Thermostat begins to open at 82–90°C and is fully open at 95–100°C; a stuck-open thermostat causes slow warm-up and weak heater output.
Coolant circulation path: water pump → engine block → cylinder head → radiator → thermostat → water pump.
Oil grade 5W-30: 5W is the cold-flow rating and 30 is the high-temperature viscosity; a lower W number gives better cold cranking.
Hot idle oil pressure is typically 1.5–4.5 bar; below about 0.5 bar the warning lamp comes on and the engine must be stopped.
The oil filter bypass valve opens when the element is clogged or the oil is cold, protecting flow at the cost of filtration.
Coolant pH should be 7.5–11.0; a hydrometer or refractometer measures freeze point, not condition alone.
Clutch, transmission, propeller shaft and differential
Clutch pedal free play is 10–20 mm; excess free play causes incomplete disengagement, while too little causes release bearing drag.
Clutch disc rivet depth minimum is about 0.3 mm above the friction lining; worn lining or oil contamination causes slip or judder.
Final drive ratio = ring gear teeth ÷ pinion teeth; a numerically higher ratio increases torque and reduces top speed.
Propeller shaft universal joint yokes must be in phase; working angles should be equal and opposite and generally below 3°.
Hypoid differential backlash is typically 0.15–0.25 mm; set pinion preload and backlash before final torque.
Manual gearbox synchronisers use cone friction; a worn blocker ring causes gear clash, especially on downshift.
Automatic transmission fluid level is checked with the engine running, transmission hot, in Park or Neutral as specified.
A split CV joint boot allows grease loss and grit entry; clicking noise on full lock indicates outer CV joint wear.
Limited-slip differentials require a friction modifier; without it, chattering occurs on tight turns.
Steering, suspension, wheels and tyres
Ackermann geometry: the inner wheel steers a larger angle than the outer wheel; toe-out on turns is normal and non-adjustable.
Positive caster improves straight-line stability and self-centring but increases steering effort; typical value is 2–8°.
Camber is wheel vertical tilt; negative camber improves cornering grip but increases inner-edge tyre wear.
Toe-in is the difference between front and rear distances across the wheels; typical total toe is 0–3 mm for passenger cars.
Tyre size 205/55 R16 means 205 mm section width, 55% aspect ratio, radial construction and a 16-inch rim.
Cold tyre pressure changes about 1 psi per 10°F (5.6°C) ambient change; set pressures when tyres are cold.
Wheel radial runout limit is typically 1.5 mm and lateral runout 1.0 mm; balance with static and dynamic correction.
Legal minimum tread depth is 1.6 mm across the central three-quarters; replace earlier for wet braking.
MacPherson strut combines spring, damper and upper pivot; a worn top mount causes knocking and changes camber.
Braking systems
Hydraulic brake force multiplication: F2 = F1 × (A2 ÷ A1); Pascal's law transmits pressure equally through the fluid.
DOT 3 dry boiling point is at least 205°C and DOT 4 at least 230°C; glycol fluids absorb moisture and should be replaced about every two years.
Brake fluid moisture above 3% lowers boiling point and risks vapour lock; test with an electronic moisture tester.
Disc brake rotor runout limit is typically 0.05 mm; minimum friction pad thickness is about 2 mm.
Bleeding sequence farthest from the master cylinder first: right rear, left rear, right front, left front.
ABS operates at roughly 5–15 cycles per second and needs wheel speed signals; a failed sensor disables ABS.
The drum brake leading shoe is self-energising; incorrect shoe placement causes unequal braking or grab.
Parking brake cable travel and rear shoe adjustment affect handbrake effectiveness; check on a slope.
Automotive electrical and electronic systems
Ohm's law: V = I × R; power P = V × I = I²R.
A 12 V lead-acid battery has six cells at about 2.1 V each; specific gravity is 1.265 when full and 1.120 when discharged.
Alternator charging voltage is 13.8–14.4 V; AC ripple above 0.5 V indicates diode failure.
Starter current draw is typically 150–250 A; cranking voltage should stay above about 9.6 V at 20°C.
High-speed CAN uses 500 kbit/s and two 120 Ω terminating resistors, giving about 60 Ω across CAN-H and CAN-L.
LIN bus runs at 19.2 kbit/s as a single-wire sub-bus for sensors and actuators.
NTC thermistor resistance falls as temperature rises; it is used for coolant and intake air temperature sensors.
Voltage drop across a good connection should be below 0.1 V at full load; test with a voltmeter while current flows.
ECU 5 V reference supplies sensors; a shorted reference pulls down all sensors on that circuit.
Vehicle diagnosis and troubleshooting
DTC P0171 means fuel system lean bank 1; causes include vacuum leak, dirty MAF, weak fuel pump or leaking injector.
Positive fuel trim means the ECU is adding fuel because the mixture is lean; negative trim means it is reducing fuel because the mixture is rich.
Compression test: hold throttle open, disable ignition and injection, crank evenly; cylinders should be within 10% of each other.
Vacuum gauge at idle should read 17–22 inHg steady; a fluctuating needle suggests valve leakage, sticking or a vacuum leak.
P0300 means random or multiple-cylinder misfire; isolate with cylinder balance or misfire counter data.
No-start diagnosis follows air, fuel, spark and compression; confirm cranking speed and battery voltage first.
Parasitic draw: key-off current is normally below 50 mA; measure with an ammeter in series after modules sleep.
Freeze-frame data records engine conditions when a DTC set; use it to reproduce the fault.
Oscilloscope checks injector and ignition waveforms for burn time, peak voltage and dwell.
Periodic servicing, vehicle inspection and workshop management
Oil change interval is commonly 5,000–10,000 km; severe duty such as short trips, dust or towing uses the shorter interval.
Air filter 15,000–30,000 km; brake fluid 2 years; coolant 2–5 years depending on type.
PDI checks include fluid levels, tyre pressures, battery, lights, road test and removal of transport protection.
Waste oil is hazardous waste: store in labelled closed containers and give it to an authorised recycler; never mix with solvents.
Refrigerant must be recovered, not vented; use a recovery machine and record the amount.
5S means sort, set in order, shine, standardise and sustain; it supports tool control and workshop safety.
Job card should record customer complaint, VIN, mileage, parts, labour and technician sign-off.
Lift safety: check rated capacity, position pads at manufacturer lift points, and lock mechanical safeties before working underneath.
Emission inspection: petrol engines are measured for CO and HC at idle and fast idle; diesel is measured for smoke opacity.
Workshop safety, tools and equipment
Torque is force times perpendicular distance: T (N·m) = F (N) × r (m); 1 kgf·m = 9.81 N·m.
Outside micrometer least count is 0.01 mm (thimble has 50 divisions; one full turn advances the spindle 0.50 mm); vernier caliper least count is 0.02 mm.
Dial gauge or DTI least count is 0.01 mm; it is used for shaft runout, brake disc runout and gear backlash.
Torque wrench accuracy is typically ±4%; recalibrate annually and after any drop or overload, checking at 20%, 60% and 100% of scale.
Jack stands must be rated for at least 1.5 times the supported load; never place any body part under a vehicle held only by a hydraulic jack.
Fire classes: A solids, B flammable liquids, C flammable gases, D metals; use CO2 or dry powder on fuel and electrical fires, never water.
Plastigauge measures bearing oil clearance by crush width; feeler gauge measures valve clearance and piston ring end gap.
Compressed air for cleaning must be below 2 bar and fitted with a safety nozzle; never direct air at skin.
Petrol exhaust contains carbon monoxide; run engines only with hose extraction, and maintain workshop ventilation of at least 10 air changes per hour.
Engine construction, operation and overhaul
Four-stroke cycle: intake, compression, power and exhaust; the crankshaft turns 720° per cycle while the camshaft turns 360°.
Displacement = (π/4) × bore² × stroke × number of cylinders.
Compression ratio = (swept volume + clearance volume) ÷ clearance volume.
Inline four-cylinder firing orders are 1-3-4-2 or 1-2-4-3; inline six-cylinder firing order is 1-5-3-6-2-4.
Valve clearance is set cold; typical intake 0.15–0.25 mm and exhaust 0.20–0.35 mm, unless the manufacturer specifies hot adjustment.
Cylinder bore taper and out-of-round are generally limited to 0.05 mm; measure at top, middle and bottom in two directions.
Piston ring end gap rule of thumb is 0.003–0.004 × bore in mm for the top ring; file-fit rings must be checked in the bore.
Torque-to-yield head bolts are tightened to a torque plus a specified angle and must be replaced, not reused.
Main bearing oil clearance is typically 0.03–0.08 mm; measure with plastigauge across the full bearing width.
Fuel supply, injection and emission control systems
Stoichiometric petrol air-fuel ratio is 14.7:1 by mass; diesel stoichiometric ratio is about 14.5:1.
Lambda λ = actual AFR ÷ stoichiometric AFR; λ = 1.00 is chemically correct, λ > 1 is lean and λ < 1 is rich.
Port fuel injection pressure is 2.5–4 bar; gasoline direct injection is 50–200 bar; common-rail diesel is 200–2,000 bar.
Three-way catalyst oxidises CO and HC and reduces NOx; it needs closed-loop lambda control oscillating near 1.00.
EGR lowers NOx by diluting the charge and reducing peak combustion temperature; typical rate is 5–20%.
DPF active regeneration burns soot at 550–650°C; frequent short journeys prevent passive regeneration and can block the filter.
Fuel trim: positive trim means the ECU adds fuel for a lean condition; long-term trim beyond ±25% usually sets a fault code.
OBD-II powertrain codes start with P; P0171 is lean bank 1 and P0300 is random or multiple-cylinder misfire.
PCV and EVAP systems control crankcase blow-by and fuel vapour; a stuck-open purge valve causes rough idle and lean codes.
Cooling and lubrication systems
A 50:50 ethylene glycol/water coolant mix gives freeze protection near −37°C and boil protection near 108°C at atmospheric pressure.
A 1 bar (about 15 psi) pressure cap raises the coolant boiling point by roughly 25°C, to about 125°C.
Thermostat begins to open at 82–90°C and is fully open at 95–100°C; a stuck-open thermostat causes slow warm-up and weak heater output.
Coolant circulation path: water pump → engine block → cylinder head → radiator → thermostat → water pump.
Oil grade 5W-30: 5W is the cold-flow rating and 30 is the high-temperature viscosity; a lower W number gives better cold cranking.
Hot idle oil pressure is typically 1.5–4.5 bar; below about 0.5 bar the warning lamp comes on and the engine must be stopped.
The oil filter bypass valve opens when the element is clogged or the oil is cold, protecting flow at the cost of filtration.
Coolant pH should be 7.5–11.0; a hydrometer or refractometer measures freeze point, not condition alone.
Clutch, transmission, propeller shaft and differential
Clutch pedal free play is 10–20 mm; excess free play causes incomplete disengagement, while too little causes release bearing drag.
Clutch disc rivet depth minimum is about 0.3 mm above the friction lining; worn lining or oil contamination causes slip or judder.
Final drive ratio = ring gear teeth ÷ pinion teeth; a numerically higher ratio increases torque and reduces top speed.
Propeller shaft universal joint yokes must be in phase; working angles should be equal and opposite and generally below 3°.
Hypoid differential backlash is typically 0.15–0.25 mm; set pinion preload and backlash before final torque.
Manual gearbox synchronisers use cone friction; a worn blocker ring causes gear clash, especially on downshift.
Automatic transmission fluid level is checked with the engine running, transmission hot, in Park or Neutral as specified.
A split CV joint boot allows grease loss and grit entry; clicking noise on full lock indicates outer CV joint wear.
Limited-slip differentials require a friction modifier; without it, chattering occurs on tight turns.
Steering, suspension, wheels and tyres
Ackermann geometry: the inner wheel steers a larger angle than the outer wheel; toe-out on turns is normal and non-adjustable.
Positive caster improves straight-line stability and self-centring but increases steering effort; typical value is 2–8°.
Camber is wheel vertical tilt; negative camber improves cornering grip but increases inner-edge tyre wear.
Toe-in is the difference between front and rear distances across the wheels; typical total toe is 0–3 mm for passenger cars.
Tyre size 205/55 R16 means 205 mm section width, 55% aspect ratio, radial construction and a 16-inch rim.
Cold tyre pressure changes about 1 psi per 10°F (5.6°C) ambient change; set pressures when tyres are cold.
Wheel radial runout limit is typically 1.5 mm and lateral runout 1.0 mm; balance with static and dynamic correction.
Legal minimum tread depth is 1.6 mm across the central three-quarters; replace earlier for wet braking.
MacPherson strut combines spring, damper and upper pivot; a worn top mount causes knocking and changes camber.
Braking systems
Hydraulic brake force multiplication: F2 = F1 × (A2 ÷ A1); Pascal's law transmits pressure equally through the fluid.
DOT 3 dry boiling point is at least 205°C and DOT 4 at least 230°C; glycol fluids absorb moisture and should be replaced about every two years.
Brake fluid moisture above 3% lowers boiling point and risks vapour lock; test with an electronic moisture tester.
Disc brake rotor runout limit is typically 0.05 mm; minimum friction pad thickness is about 2 mm.
Bleeding sequence farthest from the master cylinder first: right rear, left rear, right front, left front.
ABS operates at roughly 5–15 cycles per second and needs wheel speed signals; a failed sensor disables ABS.
The drum brake leading shoe is self-energising; incorrect shoe placement causes unequal braking or grab.
Parking brake cable travel and rear shoe adjustment affect handbrake effectiveness; check on a slope.
Automotive electrical and electronic systems
Ohm's law: V = I × R; power P = V × I = I²R.
A 12 V lead-acid battery has six cells at about 2.1 V each; specific gravity is 1.265 when full and 1.120 when discharged.
Alternator charging voltage is 13.8–14.4 V; AC ripple above 0.5 V indicates diode failure.
Starter current draw is typically 150–250 A; cranking voltage should stay above about 9.6 V at 20°C.
High-speed CAN uses 500 kbit/s and two 120 Ω terminating resistors, giving about 60 Ω across CAN-H and CAN-L.
LIN bus runs at 19.2 kbit/s as a single-wire sub-bus for sensors and actuators.
NTC thermistor resistance falls as temperature rises; it is used for coolant and intake air temperature sensors.
Voltage drop across a good connection should be below 0.1 V at full load; test with a voltmeter while current flows.
ECU 5 V reference supplies sensors; a shorted reference pulls down all sensors on that circuit.
Vehicle diagnosis and troubleshooting
DTC P0171 means fuel system lean bank 1; causes include vacuum leak, dirty MAF, weak fuel pump or leaking injector.
Positive fuel trim means the ECU is adding fuel because the mixture is lean; negative trim means it is reducing fuel because the mixture is rich.
Compression test: hold throttle open, disable ignition and injection, crank evenly; cylinders should be within 10% of each other.
Vacuum gauge at idle should read 17–22 inHg steady; a fluctuating needle suggests valve leakage, sticking or a vacuum leak.
P0300 means random or multiple-cylinder misfire; isolate with cylinder balance or misfire counter data.
No-start diagnosis follows air, fuel, spark and compression; confirm cranking speed and battery voltage first.
Parasitic draw: key-off current is normally below 50 mA; measure with an ammeter in series after modules sleep.
Freeze-frame data records engine conditions when a DTC set; use it to reproduce the fault.
Oscilloscope checks injector and ignition waveforms for burn time, peak voltage and dwell.
Periodic servicing, vehicle inspection and workshop management
Oil change interval is commonly 5,000–10,000 km; severe duty such as short trips, dust or towing uses the shorter interval.
Air filter 15,000–30,000 km; brake fluid 2 years; coolant 2–5 years depending on type.
PDI checks include fluid levels, tyre pressures, battery, lights, road test and removal of transport protection.
Waste oil is hazardous waste: store in labelled closed containers and give it to an authorised recycler; never mix with solvents.
Refrigerant must be recovered, not vented; use a recovery machine and record the amount.
5S means sort, set in order, shine, standardise and sustain; it supports tool control and workshop safety.
Job card should record customer complaint, VIN, mileage, parts, labour and technician sign-off.
Lift safety: check rated capacity, position pads at manufacturer lift points, and lock mechanical safeties before working underneath.
Emission inspection: petrol engines are measured for CO and HC at idle and fast idle; diesel is measured for smoke opacity.
Workshop safety, tools and equipment
Torque is force times perpendicular distance: T (N·m) = F (N) × r (m); 1 kgf·m = 9.81 N·m.
Outside micrometer least count is 0.01 mm (thimble has 50 divisions; one full turn advances the spindle 0.50 mm); vernier caliper least count is 0.02 mm.
Dial gauge or DTI least count is 0.01 mm; it is used for shaft runout, brake disc runout and gear backlash.
Torque wrench accuracy is typically ±4%; recalibrate annually and after any drop or overload, checking at 20%, 60% and 100% of scale.
Jack stands must be rated for at least 1.5 times the supported load; never place any body part under a vehicle held only by a hydraulic jack.
Fire classes: A solids, B flammable liquids, C flammable gases, D metals; use CO2 or dry powder on fuel and electrical fires, never water.
Plastigauge measures bearing oil clearance by crush width; feeler gauge measures valve clearance and piston ring end gap.
Compressed air for cleaning must be below 2 bar and fitted with a safety nozzle; never direct air at skin.
Petrol exhaust contains carbon monoxide; run engines only with hose extraction, and maintain workshop ventilation of at least 10 air changes per hour.
Engine construction, operation and overhaul
Four-stroke cycle: intake, compression, power and exhaust; the crankshaft turns 720° per cycle while the camshaft turns 360°.
Displacement = (π/4) × bore² × stroke × number of cylinders.
Compression ratio = (swept volume + clearance volume) ÷ clearance volume.
Inline four-cylinder firing orders are 1-3-4-2 or 1-2-4-3; inline six-cylinder firing order is 1-5-3-6-2-4.
Valve clearance is set cold; typical intake 0.15–0.25 mm and exhaust 0.20–0.35 mm, unless the manufacturer specifies hot adjustment.
Cylinder bore taper and out-of-round are generally limited to 0.05 mm; measure at top, middle and bottom in two directions.
Piston ring end gap rule of thumb is 0.003–0.004 × bore in mm for the top ring; file-fit rings must be checked in the bore.
Torque-to-yield head bolts are tightened to a torque plus a specified angle and must be replaced, not reused.
Main bearing oil clearance is typically 0.03–0.08 mm; measure with plastigauge across the full bearing width.
Fuel supply, injection and emission control systems
Stoichiometric petrol air-fuel ratio is 14.7:1 by mass; diesel stoichiometric ratio is about 14.5:1.
Lambda λ = actual AFR ÷ stoichiometric AFR; λ = 1.00 is chemically correct, λ > 1 is lean and λ < 1 is rich.
Port fuel injection pressure is 2.5–4 bar; gasoline direct injection is 50–200 bar; common-rail diesel is 200–2,000 bar.
Three-way catalyst oxidises CO and HC and reduces NOx; it needs closed-loop lambda control oscillating near 1.00.
EGR lowers NOx by diluting the charge and reducing peak combustion temperature; typical rate is 5–20%.
DPF active regeneration burns soot at 550–650°C; frequent short journeys prevent passive regeneration and can block the filter.
Fuel trim: positive trim means the ECU adds fuel for a lean condition; long-term trim beyond ±25% usually sets a fault code.
OBD-II powertrain codes start with P; P0171 is lean bank 1 and P0300 is random or multiple-cylinder misfire.
PCV and EVAP systems control crankcase blow-by and fuel vapour; a stuck-open purge valve causes rough idle and lean codes.
Cooling and lubrication systems
A 50:50 ethylene glycol/water coolant mix gives freeze protection near −37°C and boil protection near 108°C at atmospheric pressure.
A 1 bar (about 15 psi) pressure cap raises the coolant boiling point by roughly 25°C, to about 125°C.
Thermostat begins to open at 82–90°C and is fully open at 95–100°C; a stuck-open thermostat causes slow warm-up and weak heater output.
Coolant circulation path: water pump → engine block → cylinder head → radiator → thermostat → water pump.
Oil grade 5W-30: 5W is the cold-flow rating and 30 is the high-temperature viscosity; a lower W number gives better cold cranking.
Hot idle oil pressure is typically 1.5–4.5 bar; below about 0.5 bar the warning lamp comes on and the engine must be stopped.
The oil filter bypass valve opens when the element is clogged or the oil is cold, protecting flow at the cost of filtration.
Coolant pH should be 7.5–11.0; a hydrometer or refractometer measures freeze point, not condition alone.
Clutch, transmission, propeller shaft and differential
Clutch pedal free play is 10–20 mm; excess free play causes incomplete disengagement, while too little causes release bearing drag.
Clutch disc rivet depth minimum is about 0.3 mm above the friction lining; worn lining or oil contamination causes slip or judder.
Final drive ratio = ring gear teeth ÷ pinion teeth; a numerically higher ratio increases torque and reduces top speed.
Propeller shaft universal joint yokes must be in phase; working angles should be equal and opposite and generally below 3°.
Hypoid differential backlash is typically 0.15–0.25 mm; set pinion preload and backlash before final torque.
Manual gearbox synchronisers use cone friction; a worn blocker ring causes gear clash, especially on downshift.
Automatic transmission fluid level is checked with the engine running, transmission hot, in Park or Neutral as specified.
A split CV joint boot allows grease loss and grit entry; clicking noise on full lock indicates outer CV joint wear.
Limited-slip differentials require a friction modifier; without it, chattering occurs on tight turns.
Steering, suspension, wheels and tyres
Ackermann geometry: the inner wheel steers a larger angle than the outer wheel; toe-out on turns is normal and non-adjustable.
Positive caster improves straight-line stability and self-centring but increases steering effort; typical value is 2–8°.
Camber is wheel vertical tilt; negative camber improves cornering grip but increases inner-edge tyre wear.
Toe-in is the difference between front and rear distances across the wheels; typical total toe is 0–3 mm for passenger cars.
Tyre size 205/55 R16 means 205 mm section width, 55% aspect ratio, radial construction and a 16-inch rim.
Cold tyre pressure changes about 1 psi per 10°F (5.6°C) ambient change; set pressures when tyres are cold.
Wheel radial runout limit is typically 1.5 mm and lateral runout 1.0 mm; balance with static and dynamic correction.
Legal minimum tread depth is 1.6 mm across the central three-quarters; replace earlier for wet braking.
MacPherson strut combines spring, damper and upper pivot; a worn top mount causes knocking and changes camber.
Braking systems
Hydraulic brake force multiplication: F2 = F1 × (A2 ÷ A1); Pascal's law transmits pressure equally through the fluid.
DOT 3 dry boiling point is at least 205°C and DOT 4 at least 230°C; glycol fluids absorb moisture and should be replaced about every two years.
Brake fluid moisture above 3% lowers boiling point and risks vapour lock; test with an electronic moisture tester.
Disc brake rotor runout limit is typically 0.05 mm; minimum friction pad thickness is about 2 mm.
Bleeding sequence farthest from the master cylinder first: right rear, left rear, right front, left front.
ABS operates at roughly 5–15 cycles per second and needs wheel speed signals; a failed sensor disables ABS.
The drum brake leading shoe is self-energising; incorrect shoe placement causes unequal braking or grab.
Parking brake cable travel and rear shoe adjustment affect handbrake effectiveness; check on a slope.
Automotive electrical and electronic systems
Ohm's law: V = I × R; power P = V × I = I²R.
A 12 V lead-acid battery has six cells at about 2.1 V each; specific gravity is 1.265 when full and 1.120 when discharged.
Alternator charging voltage is 13.8–14.4 V; AC ripple above 0.5 V indicates diode failure.
Starter current draw is typically 150–250 A; cranking voltage should stay above about 9.6 V at 20°C.
High-speed CAN uses 500 kbit/s and two 120 Ω terminating resistors, giving about 60 Ω across CAN-H and CAN-L.
LIN bus runs at 19.2 kbit/s as a single-wire sub-bus for sensors and actuators.
NTC thermistor resistance falls as temperature rises; it is used for coolant and intake air temperature sensors.
Voltage drop across a good connection should be below 0.1 V at full load; test with a voltmeter while current flows.
ECU 5 V reference supplies sensors; a shorted reference pulls down all sensors on that circuit.
Vehicle diagnosis and troubleshooting
DTC P0171 means fuel system lean bank 1; causes include vacuum leak, dirty MAF, weak fuel pump or leaking injector.
Positive fuel trim means the ECU is adding fuel because the mixture is lean; negative trim means it is reducing fuel because the mixture is rich.
Compression test: hold throttle open, disable ignition and injection, crank evenly; cylinders should be within 10% of each other.
Vacuum gauge at idle should read 17–22 inHg steady; a fluctuating needle suggests valve leakage, sticking or a vacuum leak.
P0300 means random or multiple-cylinder misfire; isolate with cylinder balance or misfire counter data.
No-start diagnosis follows air, fuel, spark and compression; confirm cranking speed and battery voltage first.
Parasitic draw: key-off current is normally below 50 mA; measure with an ammeter in series after modules sleep.
Freeze-frame data records engine conditions when a DTC set; use it to reproduce the fault.
Oscilloscope checks injector and ignition waveforms for burn time, peak voltage and dwell.
Periodic servicing, vehicle inspection and workshop management
Oil change interval is commonly 5,000–10,000 km; severe duty such as short trips, dust or towing uses the shorter interval.
Air filter 15,000–30,000 km; brake fluid 2 years; coolant 2–5 years depending on type.
PDI checks include fluid levels, tyre pressures, battery, lights, road test and removal of transport protection.
Waste oil is hazardous waste: store in labelled closed containers and give it to an authorised recycler; never mix with solvents.
Refrigerant must be recovered, not vented; use a recovery machine and record the amount.
5S means sort, set in order, shine, standardise and sustain; it supports tool control and workshop safety.
Job card should record customer complaint, VIN, mileage, parts, labour and technician sign-off.
Lift safety: check rated capacity, position pads at manufacturer lift points, and lock mechanical safeties before working underneath.
Emission inspection: petrol engines are measured for CO and HC at idle and fast idle; diesel is measured for smoke opacity.