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MITO Light Auto L4 study materials
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MITO Light Auto L4 practice questions

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Question 1Engine and Drivetrain Systems

On a four-stroke spark-ignition engine, which sequence correctly lists the order of the strokes during one complete cycle?

  1. Power, exhaust, intake, compression
  2. Compression, intake, exhaust, power
  3. Intake, power, compression, exhaust
  4. Intake, compression, power, exhaust Correct answer.

Explanation

A complete four-stroke cycle runs intake, compression, power (combustion) and exhaust, with the crankshaft turning twice per cycle. The camshaft is driven at half crankshaft speed so that each valve opens once per cycle.

Question 2Engine and Drivetrain Systems

A rear-wheel-drive light vehicle is cornering. What is the primary job of the differential in the driven axle?

  1. To lock both driven wheels when the handbrake is applied
  2. To let each driven wheel turn at its own speed Correct answer.
  3. To hold the wheel alignment steady as the suspension moves
  4. To multiply engine torque before it reaches the road wheels

Explanation

On a turn the outer driven wheel follows a longer path than the inner one. The differential splits torque to both half-shafts while permitting a speed difference between them, which prevents tyre scrub and wind-up in the transmission.

Question 3Engine and Drivetrain Systems

On an engine oil container, what does a viscosity grade such as 5W-30 describe?

  1. The oil must be changed every 5 weeks or 30 000 km
  2. The oil's viscosity at low temperature and at 100 °C Correct answer.
  3. The oil contains 5 % additives and 30 % base stock
  4. The oil is suitable for engines up to 5 years old and 30 000 km

Explanation

The number before the W is the low-temperature grade measured under cold-cranking conditions, and the second number is the kinematic viscosity at 100 °C. A 5W oil flows more readily when cold than a 15W oil carrying the same hot grade.

Question 4Engine and Drivetrain Systems

A turbocharged petrol engine keeps exceeding its target boost and the ECU stores an overboost fault. Which component most directly limits peak boost by routing exhaust gas around the turbine?

  1. The throttle body
  2. The wastegate actuator and flap Correct answer.
  3. The intercooler bypass flap
  4. The blow-off valve on the intake side

Explanation

The wastegate is a flap in the turbine housing that opens to bypass part of the exhaust flow around the turbine wheel, capping turbine speed and therefore compressor boost. A blow-off valve only vents intake pressure spikes when the throttle closes and cannot control steady-state boost.

Question 5Engine and Drivetrain Systems

A manual-transmission car accelerates in third gear; engine speed climbs sharply while road speed rises only slowly, and a hot friction smell is noticed. Which fault best fits these symptoms?

  1. The clutch cable has too much free play
  2. The release bearing is seized and holds the clutch disengaged
  3. The gearbox synchromesh rings are worn
  4. The clutch disc is worn and slipping Correct answer.

Explanation

Engine rpm rising without a matching rise in road speed is the classic sign of clutch slip, because the friction disc can no longer transmit full engine torque. A seized release bearing or excessive cable free play causes poor disengagement or dragging, not slip under load.

Question 6Engine and Drivetrain Systems

On a front-wheel-drive car, a rhythmic clicking noise comes from the front hub area when the steering is held on full lock at low speed. Which component is the most likely cause?

  1. The clutch release bearing
  2. The front wheel bearing
  3. The gearbox input shaft bearing
  4. The outer CV joint Correct answer.

Explanation

Outer constant-velocity joints work through large steering angles, and worn balls or races produce a rhythmic clicking that is loudest on full lock. A wheel bearing normally drones with road speed and changes with cornering load, while a release bearing is heard only when the clutch pedal is operated.

Question 7Engine and Drivetrain Systems

In cold weather a car's coolant never reaches normal operating temperature, the cabin heater stays lukewarm and fuel consumption is high. What is the most likely cause?

  1. A radiator cap holding too much pressure
  2. A coolant temperature sensor reading too high
  3. A thermostat stuck open Correct answer.
  4. An airlock in the heater matrix only

Explanation

A thermostat stuck open lets coolant circulate through the radiator from a cold start, so the engine warms very slowly and the heater receives little heat. The ECU then keeps cold-start enrichment active for longer, which raises fuel consumption.

Question 8Engine and Drivetrain Systems

What is the purpose of the synchromesh (baulk ring) assembly in a manual gearbox?

  1. To match gear and shaft speeds before the dog teeth engage Correct answer.
  2. To transmit full engine torque through the selected gear
  3. To lock the gear lever in neutral when the clutch is engaged
  4. To prevent the gearbox from being shifted into reverse while moving forward

Explanation

The baulk ring rubs on the cone of the gear being selected and brings its speed close to the shaft speed before the sliding sleeve's dog teeth engage. The driving torque is then carried by the engaged dog teeth and gear teeth, not by the friction ring.

Question 9Engine and Drivetrain Systems

A diesel car used mainly for short urban trips has a repeatedly lit DPF warning lamp, a rising oil level and a smell of diesel in the oil. Which explanation fits these symptoms best?

  1. The DPF has been cleaned by a successful regeneration and the oil level is overfilled
  2. The EGR valve is stuck closed, so soot loading is falling
  3. The turbocharger seals are leaking oil into the exhaust
  4. Interrupted regenerations have washed diesel into the sump Correct answer.

Explanation

Active regeneration injects extra fuel to raise exhaust temperature, and repeated short trips can interrupt the cycle before it finishes. Unburnt diesel then reaches the cylinder walls and drains into the sump, raising the oil level and diluting the lubricant; continued use without completing a regeneration eventually chokes the filter.

Question 10Engine and Drivetrain Systems

A torque converter is fitted with a lock-up clutch. Why is that clutch engaged at a steady cruising speed?

  1. To multiply engine torque at low road speed
  2. To provide engine braking on long descents
  3. To cool the transmission fluid under load
  4. To eliminate slip at cruise and save fuel Correct answer.

Explanation

Above a defined speed the control system locks the converter clutch, mechanically joining impeller and turbine so no hydraulic slip remains. This removes the slip losses, reduces heat generation and improves fuel consumption; the clutch releases again at low speed or under heavy load to avoid stalling or harshness.

Question 11Engine and Drivetrain Systems

A light vehicle's cooling system uses a spring-loaded pressure cap on the expansion tank. What is the main purpose of that pressure cap?

  1. It filters suspended rust particles before coolant returns to the radiator.
  2. It opens the thermostat at a lower temperature when pressure rises.
  3. It raises the coolant boiling point by holding system pressure above atmospheric. Correct answer.
  4. It prevents coolant from expanding into the expansion tank when hot.

Explanation

The pressure cap holds a specified pressure in the cooling system, typically around 1 bar. Raising the pressure raises the boiling point of the coolant, so the engine can run hotter without boiling. The cap also allows coolant to pass to the expansion tank as it heats and to return as it cools, but that is a secondary function rather than the reason for pressurising the system.

Question 12Engine and Drivetrain Systems

A manual-transmission car is stationary with the engine running. The driver presses the clutch pedal and selects first gear. Which component directly pushes the pressure plate to disengage the clutch?

  1. The input shaft front bearing
  2. The clutch release bearing Correct answer.
  3. The differential carrier bearing
  4. The gearbox output shaft bearing

Explanation

When the clutch pedal is pressed, the release bearing pushes the diaphragm spring or pressure plate fingers. That movement releases the clamping force on the friction disc, so drive from the engine stops. The release bearing is therefore the part that acts directly on the pressure plate during disengagement.

Question 13Engine and Drivetrain Systems

A light vehicle has a camshaft driven by a timing belt. Which action best prevents an unexpected belt failure?

  1. Retension the belt only after a squeal becomes noticeable.
  2. Replace the belt and tensioner at the specified interval. Correct answer.
  3. Clean the belt with solvent at every oil change.
  4. Apply silicone dressing to the belt to stop a squeal at idle.

Explanation

Timing belts are consumable and can fail without warning. The specified replacement interval usually includes the tensioner and sometimes idler pulleys because bearing wear can also cause belt failure. Following the maker's interval prevents valve and piston damage on interference engines.

Question 14Engine and Drivetrain Systems

A petrol engine has a steady misfire on one cylinder. A compression test shows low pressure, but when a small amount of oil is added to the cylinder the compression rises noticeably. What does this most likely indicate?

  1. A worn camshaft lobe
  2. A burnt exhaust valve
  3. Worn piston rings and cylinder bores Correct answer.
  4. A leaking head gasket

Explanation

If compression rises when oil is added, the oil is temporarily sealing the piston rings. That points to worn rings, worn bores or both. A leaking valve or head gasket would not be sealed by added oil, so the wet result would stay low.

Question 15Engine and Drivetrain Systems

A scan tool shows a lean fault on bank 1 of a petrol engine. A smoke test finds a cracked intake boot between the mass air flow meter and the throttle body. How does the engine control unit respond to this unmetered air?

  1. It removes fuel, producing a negative long-term fuel trim.
  2. It retards ignition timing to reduce intake vacuum.
  3. It adds fuel, producing a positive long-term fuel trim. Correct answer.
  4. It commands the turbo wastegate to close fully.

Explanation

A crack after the mass air flow meter lets unmetered air into the intake. The oxygen sensor then reports a lean mixture, and the ECU adds fuel, which shows as a positive long-term fuel trim. If the leak is large enough, a lean fault code is stored.

Question 16Engine and Drivetrain Systems

A diesel car is hard to start when cold, runs roughly for the first minute and emits white smoke. The injection system and compression are known to be good. Which test is most appropriate for the suspected circuit?

  1. Check each glow plug's resistance and current draw. Correct answer.
  2. Measure the alternator charge voltage at 2000 rpm.
  3. Disconnect the crankshaft position sensor and crank the engine.
  4. Replace all injectors before testing the glow circuit.

Explanation

Cold diesel starting depends on glow plugs heating the combustion chambers. A failed plug can cause a cold misfire, white smoke and a hard start. Testing resistance and current draw identifies open or weak plugs before parts are replaced.

Question 17Engine and Drivetrain Systems

A four-wheel-drive light vehicle shudders and feels bound up when turned sharply on dry tarmac. The transfer case is a part-time type with no centre differential. What is the most likely cause?

  1. Part-time 4WD is engaged on dry tarmac with no centre differential. Correct answer.
  2. The front axle half-shafts are both broken.
  3. The ABS is applying the rear brakes continuously.
  4. The centre differential is locked and the driver must release it before turning.

Explanation

A part-time transfer case has no centre differential, so the front and rear axles must turn at the same average speed. On dry tarmac, tight turns force the tyres to scrub and the driveline to wind up. The correct action is to select two-wheel drive on high-grip surfaces.

Question 18Engine and Drivetrain Systems

A petrol engine pings under acceleration, and the knock sensor signal confirms abnormal combustion. What is the ECU's normal immediate response?

  1. Switch off the fuel pump to protect the catalyst.
  2. Open the EGR valve fully to cool the charge.
  3. Advance ignition timing until the knock stops.
  4. Retard ignition timing to stop the knock. Correct answer.

Explanation

The knock sensor detects abnormal combustion vibration in the block. The ECU responds by retarding ignition timing until the knock stops, then gradually advances it again. This protects the engine while keeping performance close to the knock limit.

Question 19Engine and Drivetrain Systems

A manual gearbox repeatedly jumps out of fourth gear when the car is accelerating or on overrun. Which inspection area is most relevant?

  1. Worn selector detent springs or gear engagement teeth Correct answer.
  2. A worn synchroniser ring that no longer matches shaft speed
  3. Too much lubricant in the gearbox
  4. A misadjusted clutch cable

Explanation

A gearbox that jumps out of gear under load or overrun usually has worn detent springs, a worn selector mechanism or worn engagement teeth. The detent holds the selector in position, and the teeth must stay fully engaged. A worn synchroniser ring would more typically cause a crunch when selecting the gear.

Question 20Engine and Drivetrain Systems

A vehicle has a top gear ratio of 0.80:1, a final drive ratio of 4.11:1 and tyres with a rolling circumference of 2.0 m. At an engine speed of 3000 rpm, what road speed does this give, to the nearest whole km/h?

  1. 95 km/h
  2. 88 km/h
  3. 137 km/h
  4. 110 km/h Correct answer.

Explanation

Wheel speed is engine speed divided by the product of gear ratio and final drive: 3000 / (0.80 × 4.11) ≈ 912 rpm. Multiply by the 2.0 m rolling circumference to get about 1825 m/min, which is about 109.5 km/h, rounded to 110 km/h.

Question 21Engine and Drivetrain Systems

On a spark-ignition engine, what is the main purpose of the positive crankcase ventilation (PCV) valve?

  1. To hold a positive pressure in the crankcase so the seals stay seated.
  2. To increase the idle air flow whenever the throttle is closed.
  3. To meter blow-by gases from the crankcase into the intake. Correct answer.
  4. To separate oil mist from fuel vapour inside the sump.

Explanation

The PCV valve controls the flow of crankcase blow-by gases into the intake so they are burned in the cylinders. It also keeps crankcase pressure slightly negative, which helps prevent oil seal leaks and oil mist escape. It is a metered ventilation path, not a pressure-holding device.

Question 22Engine and Drivetrain Systems

In a vehicle with a manual gearbox, what is the primary function of the engine flywheel?

  1. It synchronises the gearbox gears during each gear change.
  2. It multiplies engine torque before it reaches the gearbox input shaft.
  3. It drives the engine oil pump through the timing gears.
  4. It gives the clutch a friction surface and smooths torque pulses. Correct answer.

Explanation

The flywheel is bolted to the crankshaft and carries the clutch friction surface. Its mass absorbs torque pulses between combustion events, giving smoother idle and less driveline shock during gear changes. It does not multiply torque or synchronise gears.

Question 23Engine and Drivetrain Systems

In a rear-wheel-drive light vehicle, what is the main job of the final drive gear set?

  1. To let the two rear wheels rotate at different speeds during a turn.
  2. To connect and disconnect drive between the engine and gearbox.
  3. To vary the drive ratio continuously as road speed changes.
  4. To provide a fixed speed reduction and torque multiplication to the wheels. Correct answer.

Explanation

The final drive is a fixed gear pair, usually a crown wheel and pinion, that gives a permanent speed reduction. This multiplies engine torque before it reaches the driven wheels and also turns the drive through 90 degrees on a rear-wheel-drive axle. It does not allow wheel speed difference; that is the differential.

Question 24Engine and Drivetrain Systems

A coil-on-plug petrol engine misfires under heavy load. The spark plugs have been regapped much wider than specification and all coils are known good. What is the most likely reason for the misfire?

  1. The wider gap reduces the voltage needed, so the spark is too weak.
  2. The wider gap raises the voltage needed, so the coil may fail to fire. Correct answer.
  3. The wider gap lowers compression pressure and prevents ignition.
  4. The wider gap advances the ignition timing beyond the knock limit.

Explanation

A larger spark plug gap needs a higher voltage to break down the air-fuel mixture. Under heavy load the cylinder pressure is higher, so the voltage demand rises further and a marginal coil may fail to produce a spark. The result is a load-dependent misfire even though the coils test good at light load.

Question 25Engine and Drivetrain Systems

A petrol engine shows a long-term fuel trim of about -18% at both idle and cruise. Which condition best explains this reading?

  1. A leaking injector is adding unmetered fuel. Correct answer.
  2. The oxygen sensor is stuck at a lean voltage and the ECU is adding fuel.
  3. The fuel pump is delivering less pressure than the regulator specification.
  4. Unmetered air is entering the intake after the mass air flow sensor.

Explanation

A negative long-term fuel trim means the ECU is reducing injector pulse width because the exhaust oxygen sensor reports a rich mixture. A leaking injector adds fuel that is not accounted for by the air measurement, so the ECU trims fuel out at both idle and cruise. Unmetered air or low fuel pressure would create positive trim.

Question 26Engine and Drivetrain Systems

A light vehicle overheats when stationary in traffic but runs at normal temperature once road speed rises. The coolant level is correct and the radiator is not blocked. What is the most likely cause?

  1. The water pump impeller is slipping at all engine speeds.
  2. The electric radiator fan is not running when it should. Correct answer.
  3. The thermostat is stuck fully open.
  4. The pressure cap is releasing at too low a pressure.

Explanation

At idle there is little ram air through the radiator, so the electric fan must pull air through the core. If the fan does not run, coolant temperature climbs in traffic but falls once vehicle speed provides airflow. A stuck-open thermostat would normally cause overcooling, not idle-only overheating.

Question 27Engine and Drivetrain Systems

A rear-wheel-drive vehicle develops a vibration that rises with road speed and is felt through the floor around 80 km/h. It is not present when the vehicle is stationary and revved. Which area should be inspected first?

  1. The front wheel bearings and brake discs.
  2. The propeller shaft universal joints and balance weights. Correct answer.
  3. The engine mounts and exhaust downpipe.
  4. The clutch release bearing and fork.

Explanation

A vibration that tracks road speed and is felt through the floor is typical of rotating driveline components. The propeller shaft universal joints, centre bearing and balance weights are the first items to check on a rear-wheel-drive vehicle. Engine-related vibration would also appear when stationary and revving.

Question 28Engine and Drivetrain Systems

During a torque converter stall test, the engine speed is well above the manufacturer's specification in both D and R. Fluid level and linkage are correct. What does this most likely indicate?

  1. The engine is producing more torque than the transmission can handle.
  2. The forward and reverse clutches or bands are slipping. Correct answer.
  3. The transmission line pressure is higher than specification.
  4. The torque converter stator is locked and multiplying torque normally.

Explanation

In a stall test the engine is held at full throttle with the output shaft stationary, so the converter reaches its stall speed. A stall speed higher than specification in all ranges usually means the transmission is not holding the engine torque, typically because of slipping clutches or bands or low line pressure. A restricted converter or low engine power would give a lower stall speed.

Question 29Engine and Drivetrain Systems

A four-cylinder engine has a bore of 86 mm and a stroke of 86 mm. Using π = 3.142, what is the approximate total swept volume in litres?

  1. 3.0 litres
  2. 1.6 litres
  3. 2.0 litres Correct answer.
  4. 2.4 litres

Explanation

Swept volume of one cylinder is π × (bore/2)² × stroke. With an 86 mm bore and 86 mm stroke this is 3.142 × 4.3² × 8.6 ≈ 500 cm³. Four cylinders give about 2000 cm³, or 2.0 litres.

Question 30Engine and Drivetrain Systems

A manual gearbox rumbles in neutral while the engine idles with the clutch pedal released. The noise stops when the clutch pedal is pressed to the floor. Which component is most likely worn?

  1. The clutch release bearing
  2. The gearbox output shaft bearing
  3. The gearbox input shaft bearing Correct answer.
  4. The clutch pilot bearing in the crankshaft

Explanation

With the clutch pedal released in neutral, the engine still drives the gearbox input shaft, so a worn input shaft bearing rumbles. Pressing the clutch disconnects the engine and the input shaft stops turning, which makes the noise disappear. A release bearing normally makes noise when the pedal is pressed.

Question 31Engine and Drivetrain Systems

A light vehicle's oil pressure warning lamp flickers at hot idle and goes out when engine speed is raised. The oil level is correct and the engine has no abnormal knocking. Which condition most directly explains this symptom?

  1. A thermostat stuck open keeping the engine too cool
  2. Worn engine bearings lowering hot-idle oil pressure Correct answer.
  3. A fuel injector leaking extra fuel at idle speed
  4. A clutch disc slipping during acceleration

Explanation

Hot oil is thinner, so worn main and connecting-rod bearings allow excessive leakage and the pump cannot maintain pressure at idle. Raising engine speed increases pump output and the lamp goes out. The oil level being correct rules out a simple shortage.

Question 32Engine and Drivetrain Systems

A light vehicle has an automatic transmission with a dipstick. Which procedure is normally correct for checking the fluid level?

  1. Check immediately after shutdown with fluid hot and circulating
  2. Check with engine idling, fluid warm and selector in Park Correct answer.
  3. Check with the engine off and the transmission cold overnight
  4. Check with the engine idling and the selector in Drive

Explanation

Most dipstick-equipped automatic transmissions are checked with the engine idling, the fluid at normal operating temperature and the selector in Park. This fills the converter and hydraulic circuits so the dipstick reads the true level. Checking cold or with the engine off gives a misleading reading.

Question 33Engine and Drivetrain Systems

A front-wheel-drive light vehicle makes a rhythmic clicking noise from one side when turning sharply at low speed under acceleration. The noise is loudest on full lock. Which component is the most likely cause?

  1. A worn front wheel bearing
  2. A worn outer CV joint Correct answer.
  3. A collapsed engine mount
  4. A warped front brake disc

Explanation

An outer CV joint wears most in the straight-ahead position and clicks when forced to articulate on full lock under torque. The clicking is rhythmic with wheel rotation and is characteristic of a dry or pitted joint. Wheel bearings normally hum or growl rather than click on turns.

Question 34Engine and Drivetrain Systems

A light vehicle's engine warms up slowly, the heater remains lukewarm, and fuel consumption has risen slightly. The coolant level is correct and the radiator fans do not run continuously. Which fault best fits these symptoms?

  1. A leaking head gasket
  2. A thermostat stuck closed
  3. A failed water pump impeller
  4. A thermostat stuck open Correct answer.

Explanation

A thermostat stuck open lets coolant circulate through the radiator from cold start, so the engine takes too long to reach normal temperature. The heater stays lukewarm because the coolant is below the intended operating range, and the ECU may add fuel for cold running. A stuck-closed thermostat would cause rapid overheating instead.

Question 35Engine and Drivetrain Systems

A spark plug taken from a light petrol engine has a blistered insulator nose and eroded electrodes. The plug is one heat range hotter than the manufacturer specifies. Which conclusion is most justified?

  1. The plug is overheating and risks pre-ignition Correct answer.
  2. The plug is fouled by a rich fuel mixture
  3. The plug gap has closed because of detonation
  4. The ignition timing is retarded at idle speed

Explanation

A blistered insulator nose and eroded electrodes are signs of excessive plug temperature. A plug one heat range too hot cannot shed heat quickly enough and can become a glow source, leading to pre-ignition. Correct heat range and torque are essential.

Question 36Engine and Drivetrain Systems

A turbocharged diesel light vehicle sets an overboost fault and derates under hard acceleration. The wastegate actuator is seized in the fully closed position. What is the most direct result?

  1. Exhaust cannot bypass the turbine, raising boost above target Correct answer.
  2. The intercooler is bypassed and intake air temperature falls
  3. All exhaust gas bypasses the turbine and boost falls to zero
  4. The compressor wheel stops turning and intake airflow is blocked

Explanation

The wastegate is the exhaust bypass around the turbine. If the actuator holds it closed, all exhaust flow drives the turbine and compressor speed rises until boost exceeds the ECU target. The ECU then cuts fuel or limits boost to protect the engine.

Question 37Engine and Drivetrain Systems

A manual-transmission light vehicle's engine speed rises sharply when accelerating in third gear, but road speed increases only slowly. The clutch pedal has normal free play. Which fault best explains this?

  1. A worn clutch disc Correct answer.
  2. A noisy clutch release bearing
  3. A worn outer CV joint
  4. A worn gearbox synchromesh ring

Explanation

Engine speed rising without a matching rise in road speed means the clutch is slipping under torque. A worn or oil-contaminated friction disc cannot transmit the full engine torque, so slip increases in higher gears. Normal pedal free play makes a misadjusted release mechanism less likely.

Question 38Engine and Drivetrain Systems

A rear-wheel-drive light vehicle has a whine from the rear axle that is loudest on light acceleration and quieter on overrun. Which inspection area is most appropriate?

  1. Differential ring-and-pinion backlash and oil Correct answer.
  2. Engine mount alignment and exhaust hanger clearance
  3. Front wheel bearing preload and grease condition
  4. Transmission input shaft bearing end float

Explanation

A whine that changes between acceleration and overrun is typical of final-drive gear wear or incorrect ring-and-pinion backlash. Checking the rear axle oil for metallic particles and measuring backlash and contact pattern is the correct next step. Front bearings and engine mounts would not produce a rear-axle whine tied to drive torque.

Question 39Engine and Drivetrain Systems

A petrol engine stores a camshaft timing over-advanced fault on bank 1. The oil has been changed irregularly, and the variable valve timing solenoid screen is partly blocked with sludge. Which mechanism best explains the fault?

  1. A sticking fuel injector raises fuel pressure and advances cam timing
  2. Restricted oil flow stops the phaser returning to base timing Correct answer.
  3. Long ignition coil dwell overheats the spark plug and advances cam timing
  4. A slow knock sensor retards ignition timing and advances the camshaft

Explanation

Variable valve timing phasers are moved by engine oil pressure controlled through the solenoid. A blocked solenoid screen reduces oil flow, so the phaser can stick in an advanced position and the camshaft position no longer matches the commanded target. Cleaning or replacing the solenoid and correcting the oil condition is the repair path.

Question 40Engine and Drivetrain Systems

A high-mileage gasoline direct-injection engine has rough idle, misfires and reduced power. Intake valve carbon deposits are found. Which design characteristic best explains why this occurs more than in port-injection engines?

  1. The intake valves are cooled by fuel spray in direct-injection engines
  2. Direct injection uses a richer mixture at all times, which leaves carbon
  3. Fuel is injected into the cylinder, not onto the intake valves Correct answer.
  4. The PCV system is deleted on direct-injection engines

Explanation

In a port-injection engine, petrol is sprayed upstream of the intake valve and its solvent action helps keep the valve back clean. With direct injection, only air passes the intake valve, so crankcase vapours and oil mist can bake onto the hot valve. This promotes carbon buildup, rough idle and misfire.

Question 41Electrical and Electronic Systems

Which battery rating specifies the current a 12 V battery can deliver for 30 seconds at -18 °C while maintaining at least 7.2 V?

  1. Cold cranking amps (CCA) Correct answer.
  2. Cranking amps (CA)
  3. Ampere-hour capacity (Ah)
  4. Reserve capacity (RC)

Explanation

CCA is defined by a cold-temperature cranking test: 30 seconds at -18 °C with the battery held at or above 7.2 V. Reserve capacity measures how long the battery can supply a small load before voltage falls, and ampere-hour capacity describes charge storage rather than cold cranking performance.

Question 42Electrical and Electronic Systems

A 15 A blade fuse protecting a lighting circuit has blown. Which replacement fuse is correct?

  1. A 20 A fuse of the same physical size
  2. A 30 A fuse if the lighting load has been upgraded
  3. A 15 A fuse with the same interrupt rating Correct answer.
  4. A 10 A fuse to provide extra protection

Explanation

A fuse must be replaced with the same current rating and a voltage and interrupt rating suitable for the circuit. Installing a higher-rated fuse allows excessive current to flow before the fuse opens, while a lower-rated fuse may blow under normal load.

Question 43Electrical and Electronic Systems

To measure the voltage available at a headlamp connector while the lamp is switched on, how should a digital multimeter be connected?

  1. Between the lamp positive terminal and battery negative, with the lamp disconnected
  2. Between the two headlamp terminals after removing the lamp from the circuit
  3. Across the lamp positive and ground terminals with the lamp operating Correct answer.
  4. In series with the lamp, with the lamp removed

Explanation

Voltage is measured in parallel with the circuit while the circuit is loaded. Backprobing the positive and ground terminals with the lamp connected and operating reveals the actual voltage delivered under load, which is more useful than an unloaded reading.

Question 44Electrical and Electronic Systems

During a starter voltage-drop test, the voltmeter reads 0.9 V across the positive cable from battery to starter while cranking. What does this indicate?

  1. Normal cable resistance; continue the test
  2. Excessive cable or connection resistance Correct answer.
  3. An open circuit in the starter control circuit
  4. A battery that is overcharged

Explanation

Voltage drop is measured across a conductor while current flows, and excessive drop means the conductor or its connections are resisting current. A reading of 0.9 V on a starter positive cable is well above typical limits and points to high resistance in the cable, terminals, or connections.

Question 45Electrical and Electronic Systems

A charging system has normal DC output voltage but excessive AC voltage when measured at the battery with the engine running. Which alternator component is most likely faulty?

  1. The drive belt tensioner
  2. The rotor slip rings
  3. The voltage regulator
  4. A rectifier diode Correct answer.

Explanation

The alternator produces AC that the rectifier converts to DC, and a failed diode allows excessive AC ripple to appear at the battery. Normal DC output with high AC voltage therefore points to the rectifier rather than to the regulator or belt drive.

Question 46Electrical and Electronic Systems

On a standard ISO 4-pin automotive relay, which pair of terminals is connected to the electromagnetic coil?

  1. Terminals 85 and 86 Correct answer.
  2. Terminals 30 and 86
  3. Terminals 87 and 87a
  4. Terminals 30 and 87

Explanation

In the standard ISO relay numbering, terminals 85 and 86 are the coil circuit that creates the magnetic field. Terminal 30 is the common contact, 87 is the normally open contact, and 87a is the normally closed contact.

Question 47Electrical and Electronic Systems

With the ignition off, a CAN bus measures 60 Ω between CAN High and CAN Low. What is the correct interpretation?

  1. One terminating resistor is open
  2. Both 120 Ω terminators are connected in parallel Correct answer.
  3. The bus is shorted to ground
  4. The bus is shorted together, so communication cannot occur

Explanation

A CAN bus normally has two 120 Ω terminating resistors, one near each end of the bus, and they appear in parallel when measured across CAN High and CAN Low. Two 120 Ω resistors in parallel produce approximately 60 Ω, so this reading is normal.

Question 48Electrical and Electronic Systems

A three-wire sensor shares a 5 V reference with other sensors. With the sensor disconnected and ignition on, the reference circuit measures 0.4 V. What is the most likely cause?

  1. The PCM has commanded a low reference voltage
  2. The 5 V reference circuit is shorted to ground Correct answer.
  3. The reference circuit has excessive resistance to the PCM
  4. The sensor is producing a normal signal

Explanation

With the sensor disconnected, the 5 V reference circuit should measure close to 5 V because the meter draws almost no current. A reading of 0.4 V indicates that the reference line is being pulled down, most commonly by a short to ground or another sensor loading the shared reference.

Question 49Electrical and Electronic Systems

After all modules have entered sleep, a parasitic draw test shows 35 mA on a vehicle with a 60 Ah battery. What is the most appropriate next step?

  1. Compare the reading with the manufacturer's specified maximum draw Correct answer.
  2. Replace the battery because any draw above 20 mA is unacceptable
  3. Begin removing fuses one at a time until the draw falls to zero
  4. Install a battery with a higher ampere-hour rating

Explanation

Acceptable parasitic draw varies by vehicle and by how long the modules have been asleep, and many manufacturers allow a small sleep current in the tens of milliamperes. The measured value should be compared with the vehicle-specific specification before parts are replaced or circuits are disturbed.

Question 50Electrical and Electronic Systems

A Hall-effect crankshaft position sensor receives 5 V reference and ground. With the sensor connected and the engine cranking, the signal wire remains at a steady 5 V. Technician A says the signal circuit may be open. Technician B says the sensor may be internally open. Who is correct?

  1. Technician A only; an open signal circuit is the only cause
  2. Neither technician; the PCM reference is faulty
  3. Both Technician A and Technician B Correct answer.
  4. Technician B only; an open sensor is the only cause

Explanation

A Hall-effect signal circuit is typically pulled up to a high voltage and switched low by the sensor. An open signal circuit or a sensor that cannot pull the signal low can both leave the signal stuck at 5 V, so both technicians are describing possible causes.