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ASE A8 practice questions

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Question 1General Engine Diagnosis

An engine uses a quart of oil every 500 miles. There are no external leaks, the spark plugs are dry, and the exhaust shows a continuous blue-gray haze at all speeds. Which is the most likely cause?

  1. A restricted PCV hose
  2. A leaking intake manifold coolant passage
  3. Worn piston rings Correct answer.
  4. Worn valve stem seals only

Explanation

Oil smoke that is present continuously at all speeds with dry plugs and no external leaks points to oil passing the piston rings into the combustion chamber. Valve stem seal leakage usually produces smoke mainly after an idle period or on startup rather than a constant haze.

Question 2General Engine Diagnosis

A compression test on a warm engine gives 95 psi on cylinder 3 while the other cylinders are 150 to 160 psi. Adding two tablespoons of oil to cylinder 3 raises its reading to 150 psi. What does this indicate?

  1. A blown head gasket
  2. A jumped timing chain
  3. A leaking exhaust valve
  4. Worn piston rings Correct answer.

Explanation

When compression rises substantially after oil is added, the oil is temporarily sealing the piston rings, which identifies the rings and cylinder wall as the source of the leak. Leakage past a valve or the head gasket is not sealed by oil added to the cylinder.

Question 3General Engine Diagnosis

An engine loses coolant with no visible external leak, and white sweet-smelling steam leaves the tailpipe. Which test most directly confirms the diagnosis?

  1. A cooling system pressure test held for 30 minutes
  2. A chemical test of the coolant for exhaust gases Correct answer.
  3. A cylinder leakage test
  4. A thermostat opening test

Explanation

A chemical block test detects combustion gases dissolved in the coolant, which confirms a breach between the combustion chamber and the cooling jacket. A pressure test only proves the system leaks somewhere and cannot tell whether combustion gases are entering it.

Question 4General Engine Diagnosis

Engine oil pressure is below specification at all speeds. The oil level and viscosity are correct and the gauge has been verified against a known-good mechanical gauge. Which is the most likely cause?

  1. A relief valve stuck closed
  2. A faulty oil temperature sensor
  3. A restricted oil filter bypass
  4. Worn crankshaft bearing clearances Correct answer.

Explanation

Low pressure at all speeds with the right oil and an accurate gauge means oil is escaping through excessive clearances inside the engine, typically at the main and rod bearings. A relief valve stuck closed would raise pressure, and a restricted filter simply opens its bypass.

Question 5General Engine Diagnosis

A rhythmic metallic ticking from under the valve cover at idle that speeds up with engine rpm is most likely caused by which condition?

  1. Excessive piston-to-wall clearance
  2. A worn main bearing
  3. A leaking exhaust manifold gasket
  4. A collapsed hydraulic lifter Correct answer.

Explanation

A rhythmic top-end tick that follows engine speed is the classic sign of excessive valve lash or a lifter that will not hold oil, letting the pushrod or rocker slap. Bearing knock is deeper and lower in the engine, and piston noise is a hollow cold-start rattle.

Question 6General Engine Diagnosis

Black smoke from the exhaust during acceleration indicates which condition?

  1. Coolant entering the cylinders
  2. A lean air/fuel ratio
  3. Oil passing the valve guides
  4. Too rich an air/fuel mixture Correct answer.

Explanation

Black smoke is soot from fuel that was not completely burned, which means the mixture is too rich for the air available. Blue smoke comes from burning oil, and white smoke or steam comes from coolant.

Question 7General Engine Diagnosis

A vehicle has a rough idle, an oil leak at the valve cover gasket, and a whistling noise from the crankcase area. Which is the most likely cause?

  1. A weak ignition coil
  2. A leaking fuel injector
  3. A clogged PCV valve Correct answer.
  4. A stuck-open thermostat

Explanation

A clogged PCV valve lets crankcase pressure build until oil is forced past seals and gaskets, and escaping pressure can whistle. The rough idle results from crankcase vapors backing up into the intake instead of being drawn out in a controlled way.

Question 8General Engine Diagnosis

A customer complains of a vibration felt through the seat and steering wheel that is worst at idle with the transmission in gear and disappears when the transmission is shifted to neutral or the engine speed is raised. Which is the most likely cause?

  1. An out-of-balance tire
  2. A worn CV joint
  3. A worn engine or transmission mount Correct answer.
  4. A bent wheel

Explanation

A vibration that exists only at idle under load and disappears in neutral is engine torque reaction that a worn mount can no longer absorb. Tire, wheel, and CV joint vibrations vary with road speed rather than with engine load at a standstill.

Question 9General Engine Diagnosis

A vacuum gauge connected to the intake manifold reads a steady average of about 16 in-Hg at idle, but the needle flutters rapidly between 10 and 19 in-Hg. Which is the most likely cause?

  1. Retarded ignition timing
  2. A leaking intake gasket
  3. Worn valve guides Correct answer.
  4. A restricted exhaust system

Explanation

A needle that flutters quickly at idle shows uneven intake airflow, which is typical of worn valve guides or sticking valves. A vacuum leak or retarded timing produces a steady low reading instead of a rapid flutter.

Question 10General Engine Diagnosis

During a cylinder leakage test on cylinder 2, air is heard escaping from the oil filler opening. Where is the leakage?

  1. The piston rings Correct answer.
  2. The head gasket
  3. The intake valve
  4. The exhaust valve

Explanation

Air reaching the crankcase and escaping at the oil filler or dipstick tube has passed the piston rings. Leakage at an intake valve is heard at the throttle body, at an exhaust valve at the tailpipe, and at the head gasket as bubbles in the cooling system.

Question 11General Engine Diagnosis

An engine takes a long time to reach operating temperature, the heater delivers lukewarm air, and the upper radiator hose stays cool while the engine warms. Which is the most likely cause?

  1. A failed water pump
  2. A leaking radiator cap
  3. A thermostat stuck closed
  4. A thermostat stuck open Correct answer.

Explanation

A thermostat stuck open lets coolant circulate through the radiator from a cold start, so the engine warms slowly and heater output stays weak. A thermostat stuck closed causes rapid overheating instead of slow warm-up.

Question 12General Engine Diagnosis

Engine oil on the dipstick appears milky and smells of coolant. Which is the most likely cause?

  1. A plugged PCV valve
  2. Extended oil change intervals
  3. A leaking transmission cooler in the radiator
  4. A failed head gasket or cracked head Correct answer.

Explanation

Milky, coolant-smelling oil means coolant is mixing with the oil, most often through a failed head gasket or a cracked casting. A transmission cooler leak inside the radiator contaminates the transmission fluid or the cooling system, not the engine oil.

Question 13General Engine Diagnosis

A deep, dull knock from the lower engine is loudest during acceleration and is accompanied by low oil pressure at idle. Which is the most likely cause?

  1. A worn rod bearing Correct answer.
  2. Piston slap
  3. A collapsed lifter
  4. A loose accessory belt

Explanation

A heavy knock from the lower engine that worsens under load and comes with low oil pressure is typical of excessive connecting rod bearing clearance. Lifter noise is a top-end tick, piston slap is a cold-start rattle, and belt noise is a squeal.

Question 14General Engine Diagnosis

A sharp, hollow knock is heard when the engine is cold and gradually fades as the engine reaches operating temperature. Which is the most likely cause?

  1. A worn timing chain tensioner
  2. Spark knock from low-octane fuel
  3. A worn main bearing
  4. Excessive piston clearance Correct answer.

Explanation

Pistons are fitted with clearance for thermal expansion, so worn or improperly fitted pistons rock in the bore and knock when cold, then quiet down as they expand. Main bearing knock does not fade with temperature and is a deeper sound.

Question 15General Engine Diagnosis

A pinging noise is heard under acceleration on an otherwise healthy engine. Which condition is the most likely cause?

  1. Fuel with too low an octane rating Correct answer.
  2. A thermostat stuck open
  3. An excessively rich air/fuel mixture
  4. Over-retarded base ignition timing

Explanation

Spark knock occurs when the air/fuel charge ignites from heat and pressure instead of the spark, and low-octane fuel resists that pressure poorly. Rich mixtures and retarded timing both tend to reduce knock rather than cause it.

Question 16General Engine Diagnosis

A vacuum gauge reads about 18 in-Hg at idle but falls steadily toward 5 in-Hg when engine speed is held at 2500 rpm. Which condition does this indicate?

  1. A vacuum leak
  2. Worn piston rings
  3. A lean misfire at high rpm
  4. A restricted exhaust system Correct answer.

Explanation

Vacuum that holds at idle but drops away as speed is held indicates rising exhaust backpressure, which prevents cylinders from filling. A vacuum leak or worn rings produces a low but steady reading that does not continue to fall with rpm.

Question 17General Engine Diagnosis

During a power balance test, disabling the injector for cylinder 4 produces no change in idle quality or engine speed, while disabling each of the other cylinders causes a noticeable drop. What does this indicate?

  1. Fuel pressure is too high
  2. Cylinder 4 is misfiring Correct answer.
  3. The PCV valve is stuck open
  4. Ignition timing is retarded

Explanation

Cancelling a cylinder that is working normally causes an rpm drop and rougher running, so no change means that cylinder was already contributing nothing. The test identifies the weak cylinder but does not by itself identify the cause.

Question 18General Engine Diagnosis

A rattle from the front of the engine is heard only for a second or two after a cold start, then disappears. Which is the most likely cause?

  1. A leaking exhaust manifold gasket
  2. A worn serpentine belt
  3. A worn timing chain tensioner Correct answer.
  4. A loose spark plug

Explanation

When the tensioner bleeds down overnight, the chain is loose for the first seconds after startup until oil pressure refills it, producing a brief rattle. A leaking exhaust gasket is a constant puff, a loose plug ticks constantly, and a belt squeals.

Question 19General Engine Diagnosis

An engine cranks at an even, normal speed but will not start. Testing shows good spark at all plugs and no fuel pressure at the service port. Which is the most likely cause?

  1. A failed fuel pump Correct answer.
  2. Low engine compression
  3. A faulty ignition coil
  4. A jumped timing chain

Explanation

Good spark at every plug with no fuel pressure places the fault in the fuel delivery side, so the pump, its relay, and its circuit are the next checks. A jumped chain or low compression would normally show up as an uneven or unusually fast cranking speed.

Question 20General Engine Diagnosis

An engine overheats in stop-and-go traffic but runs at normal temperature on the highway. Which is the most likely cause?

  1. A thermostat stuck open
  2. An inoperative electric cooling fan Correct answer.
  3. A restricted heater core
  4. A leaking head gasket

Explanation

Overheating only at low speed means radiator airflow depends on the fan, which is not running. Ram air at highway speed keeps the engine cool even with a dead fan, while a thermostat or head gasket fault would overheat at all speeds.

Question 21General Engine Diagnosis

A compression test shows 60 psi on cylinders 3 and 4, which are adjacent in the block, and 150 psi on all the other cylinders. Adding oil does not change the readings on 3 and 4. What is the most likely cause?

  1. Two collapsed lifters
  2. A head gasket leak between 3 and 4 Correct answer.
  3. A worn camshaft lobe
  4. Worn oil control rings in both cylinders

Explanation

Two adjacent cylinders with equally low compression that does not respond to added oil points to a gasket breach between them, so both cylinders share the same leak path. Ring wear would improve with oil, and cam or lifter faults usually affect only one cylinder.

Question 22General Engine Diagnosis

A cylinder leakage test on one cylinder shows 35 percent leakage, and air bubbles steadily out of the radiator with the cap removed. What does this indicate?

  1. Worn piston rings
  2. A leaking intake manifold gasket
  3. A burned exhaust valve
  4. A cracked head or head gasket Correct answer.

Explanation

Bubbles in the cooling system during a leakage test show that compressed air is being forced into the coolant jackets, which means the head gasket or a casting is breached. Ring, intake valve, and exhaust valve leakage show up at the crankcase, throttle body, and tailpipe.

Question 23General Engine Diagnosis

Used oil analysis on an engine with no reported symptoms shows elevated sodium and potassium with normal wear metals. What does this indicate?

  1. Dust ingestion through the intake
  2. Fuel dilution from short trips
  3. Coolant contamination Correct answer.
  4. Excessive bearing wear

Explanation

Sodium and potassium are used as corrosion inhibitors in coolant, so they show up in oil analysis when coolant is seeping into the crankcase. Bearing wear raises lead, copper, and tin, fuel dilution raises fuel markers, and dust shows up as silicon.

Question 24General Engine Diagnosis

A cylinder has 150 psi static compression, good spark, and a pulsing injector, yet it contributes little to power balance. A running compression test shows no increase in pressure when the throttle is snapped open. Which is the most likely cause?

  1. Worn piston rings
  2. A clogged fuel injector
  3. A faulty spark plug
  4. A worn camshaft lobe Correct answer.

Explanation

Running compression that does not rise when the throttle is snapped means the cylinder cannot take in extra air, which points to a camshaft lobe that no longer opens the valve fully. Ring, plug, and injector faults would have shown up in the static compression, spark, and injector tests.

Question 25General Engine Diagnosis

An engine has a knock that is loudest at 2000 rpm and becomes noticeably quieter when the No. 3 spark plug wire is grounded. What does this tell the technician?

  1. The noise is from an accessory drive
  2. The noise is related to cylinder 3 Correct answer.
  3. The noise is in the timing chain
  4. The noise is an exhaust leak

Explanation

Grounding a plug wire cancels that cylinder's power stroke, so a knock that changes only when one cylinder is cut is produced by that cylinder's rod, piston, or bearing. Timing chain and accessory noises do not respond to cylinder cutout.

Question 26General Engine Diagnosis

A cylinder produces 90 psi on a dry compression test. After a small amount of engine oil is squirted into the cylinder, compression rises to 140 psi. What does this result indicate?

  1. A blown head gasket
  2. Worn piston rings Correct answer.
  3. A worn camshaft lobe
  4. A leaking intake valve

Explanation

The added oil temporarily seals the gap between the rings and the cylinder wall, so a large pressure increase after oiling points to ring and cylinder wall sealing as the problem. A rise of roughly 10 to 15 percent or more over the dry reading is the usual threshold for condemning rings. Leakage past valves or the head gasket is not sealed by oil, so those faults leave the reading essentially unchanged.

Question 27General Engine Diagnosis

Technician A says all spark plugs should be removed and the throttle held wide open during a compression test. Technician B says the battery must be fully charged so the engine cranks at normal speed. Who is correct?

  1. Technician A only
  2. Both A and B Correct answer.
  3. Technician B only
  4. Neither A nor B

Explanation

Removing all plugs and propping the throttle open lets each cylinder fill with air and removes the drag of compression from the other cylinders, giving consistent, comparable readings. Cranking speed directly affects the pressure a cylinder can build, so a weak battery produces falsely low numbers. Both procedures are required for a valid test.

Question 28General Engine Diagnosis

An engine emits a puff of blue-gray smoke on the first start after sitting overnight, then runs clean with no visible smoke for the rest of the day. Which is the most likely cause?

  1. A leaking fuel injector
  2. Worn valve stem seals Correct answer.
  3. A restricted PCV valve
  4. Worn piston rings

Explanation

Oil that seeps past worn valve stem seals and guides while the engine sits collects on top of the pistons and burns off in the first few seconds of running. Once the oil is consumed, the exhaust clears and stays clear. Ring wear, by contrast, produces smoke that continues during running, especially under acceleration.

Question 29General Engine Diagnosis

On a fully warmed engine, a scan tool displays an engine coolant temperature of minus 40 degrees Fahrenheit, and long-term fuel trims are heavily positive on both banks. Which is the most likely cause?

  1. An open ECT signal circuit Correct answer.
  2. A shorted ECT signal wire
  3. High fuel pressure
  4. A thermostat stuck open

Explanation

An open in the coolant sensor signal circuit drives the reported temperature to the extreme cold end of the scale. The PCM reacts to a cold engine by enriching the mixture, which shows up as large positive fuel trims. The actual engine temperature is normal, so the reading is a circuit fault rather than a cooling problem.

Question 30General Engine Diagnosis

An engine idles smoothly but misfires under heavy acceleration and at steady highway cruise. Which condition most directly explains a misfire that appears only under load?

  1. A restricted air filter element
  2. A thermostat that opens late
  3. A knock sensor with an open circuit
  4. Excessively worn spark plug gap Correct answer.

Explanation

A gap worn wider than specification raises the voltage needed to jump the gap. Cylinder pressure rises sharply under load, which further raises the required firing voltage, so the ignition system can no longer fire the plug reliably. At idle, required voltage is low enough that the same plug still fires normally.

Question 31General Engine Diagnosis

An exhaust backpressure test is performed at the upstream oxygen sensor port, and the gauge reads 4 psi while the engine is held at 2500 rpm. What does this reading indicate?

  1. A leaking exhaust manifold gasket
  2. Normal exhaust backpressure for the engine speed
  3. A restricted catalytic converter Correct answer.
  4. An intake manifold vacuum leak

Explanation

Backpressure measured ahead of the converter should generally stay below about 1.5 psi at 2500 rpm. A reading of 4 psi signals a significant restriction downstream, most often a melted or plugged catalytic converter. The restriction also typically causes low intake manifold vacuum and reduced power.

Question 32General Engine Diagnosis

Fuel pressure is at specification at idle, but it falls below specification during a road test under heavy acceleration and then recovers. Which is the most likely cause?

  1. A defective fuel pump check valve
  2. A purge solenoid stuck open
  3. A leaking fuel injector
  4. A restricted in-line fuel filter Correct answer.

Explanation

At idle the engine uses very little fuel volume, so a restriction upstream of the rail can still hold normal pressure. Under load, volume demand rises and a restricted filter or a weak pump cannot keep up, so pressure sags. The recovery when load drops confirms a volume delivery problem rather than a regulator fault.

Question 33General Engine Diagnosis

Cranking compression, cylinder leakage, and spark all test normal on cylinder 5, but a running compression test shows cylinder 5 far below the other cylinders, and the reading does not rise when the throttle is snapped open. Which is the most likely cause?

  1. A leaking head gasket
  2. A restricted catalytic converter
  3. Worn piston rings
  4. A worn camshaft lobe Correct answer.

Explanation

Running compression measures how well the cylinder moves air while the engine operates. A reading that stays low and fails to rise on snap throttle means the valve is not opening far enough to admit air, which points to a flat cam lobe, bent pushrod, or similar valvetrain fault. Ring and head gasket faults would already show on the cranking and leakage tests.

Question 34General Engine Diagnosis

Base ignition timing is set correctly, but with a timing light the mark wanders erratically back and forth at a steady idle. Which is the most likely cause?

  1. A leaking vacuum advance unit
  2. Spark plugs gapped too wide
  3. A worn timing chain Correct answer.
  4. A clogged fuel filter

Explanation

Erratic timing scatter at a steady speed means the relationship between the crankshaft and the camshaft or distributor drive is changing. Slack in the timing chain or a worn distributor drive gear allows that relationship to shift unpredictably. A steady offset, rather than random wander, would point to a base timing or advance fault.

Question 35General Engine Diagnosis

A warm engine in closed loop has a zirconia oxygen sensor signal that switches, but the average is about 0.85 volt. What does this indicate?

  1. The sensor heater is open and the signal is not yet valid.
  2. The mixture is rich and the PCM will shorten injector pulse width. Correct answer.
  3. The mixture is lean and the PCM will lengthen injector pulse width.
  4. The mixture is at stoichiometry and the sensor is behaving normally.

Explanation

A narrowband zirconia sensor produces a voltage that rises as the exhaust gets richer; an average well above 0.45 volt means the mixture is rich overall. The PCM responds by reducing fuel delivery, which shows up as negative fuel trim.

Question 36General Engine Diagnosis

A vehicle has short term fuel trim of +22% at idle that falls to about +4% at 2,500 rpm. Which is the most likely cause?

  1. A restricted fuel filter
  2. An intake vacuum leak Correct answer.
  3. A weak ignition coil
  4. A leaking fuel injector

Explanation

A trim that is strongly positive only at idle and normalizes as airflow increases points to unmetered air entering downstream of the throttle. The leak is a large fraction of total airflow at idle and a small fraction at higher rpm.

Question 37General Engine Diagnosis

With the sensor disconnected and the key on, a sensor's 5-volt reference terminal measures 0.3 volt. What is the most likely cause?

  1. A short to voltage in the reference circuit
  2. An open in the reference circuit
  3. A short to ground in the reference circuit Correct answer.
  4. A normal unloaded reference reading

Explanation

The PCM regulates the reference to about 5.0 volts. With the sensor load removed, a reading near ground means the conductor or a shared splice is being pulled to ground.

Question 38General Engine Diagnosis

A fully warmed engine shows an ECT signal of about -40 degrees F, and the sensor circuit measures at very high resistance. What will the PCM most likely do?

  1. Command a lean mixture and advance timing
  2. Command a rich mixture and set a low temperature code Correct answer.
  3. Set a code for an overheated engine
  4. Default to a fixed 200 degrees F value and ignore the sensor

Explanation

The ECT sensor is an NTC thermistor, so high resistance is interpreted as extreme cold. The PCM then adds fuel and raises idle speed, and it will typically set a circuit or rationality code.

Question 39General Engine Diagnosis

Which statement correctly describes MAP sensor output on a speed-density engine control system?

  1. Signal voltage rises as manifold vacuum rises.
  2. Signal voltage rises as manifold absolute pressure rises. Correct answer.
  3. Signal voltage stays fixed once the key is on.
  4. Signal voltage follows engine rpm regardless of load.

Explanation

A MAP sensor measures absolute pressure in the intake manifold. Low vacuum such as wide open throttle produces high pressure and high signal voltage, while high vacuum at idle produces low voltage.

Question 40General Engine Diagnosis

A scan tool shows DTC P0300. What does this code report?

  1. Random or multiple cylinder misfire Correct answer.
  2. Oxygen sensor heater circuit fault
  3. Misfire in cylinder 1 only
  4. Catalyst efficiency below threshold

Explanation

P0300 is the generic code for a misfire that the PCM cannot attribute to a single cylinder. Codes P0301 through P0308 identify a specific cylinder.

Question 41General Engine Diagnosis

Which condition must be met before the PCM will enter closed loop fuel control?

  1. The throttle must be at wide open
  2. The fuel tank must be more than half full
  3. The oxygen sensors must switch reliably Correct answer.
  4. Coolant temperature must be below 100 degrees F

Explanation

Closed loop requires feedback the PCM can trust, which means a warmed oxygen sensor producing a usable switching signal. Until that happens the PCM runs open loop on stored tables.

Question 42General Engine Diagnosis

What is the primary job of the crankshaft position sensor?

  1. Reporting crankshaft speed and position to the PCM Correct answer.
  2. Detecting detonation in the cylinders
  3. Reporting camshaft position for sequential injection
  4. Reporting vehicle speed to the PCM

Explanation

The CKP signal tells the PCM how fast the crank is turning and where it is in rotation, which drives ignition timing, injector timing, and misfire detection.

Question 43General Engine Diagnosis

A DTC is set and the scan tool displays freeze frame data. What does this data represent?

  1. The highest and lowest values seen since the last key cycle
  2. Live data from the current drive cycle only
  3. The learned adaptive values held in keep-alive memory
  4. Operating conditions captured when the fault was stored Correct answer.

Explanation

Freeze frame stores a snapshot of parameters such as rpm, load, coolant temperature, and fuel trim at the moment the code matured. It lets a technician reproduce the conditions that triggered the fault.

Question 44General Engine Diagnosis

What information does OBD-II Mode $06 provide?

  1. Pending codes that have not yet matured
  2. The vehicle identification number
  3. Freeze frame data for stored codes
  4. Results of on-board monitor tests Correct answer.

Explanation

Mode $06 returns raw test values and limits for non-continuously monitored systems, which helps identify a monitor that is marginal but has not yet set a code.

Question 45General Engine Diagnosis

After clearing codes, a technician scans readiness monitors and finds several incomplete. What is the correct action?

  1. Disconnect the battery to speed up monitor completion
  2. Clear the codes again to force the monitors to complete
  3. Drive the vehicle through the appropriate drive cycle Correct answer.
  4. Replace the PCM because the monitors will not reset

Explanation

Clearing codes resets the readiness monitors, and each monitor only completes after its enabling conditions are met during a drive cycle. Clearing again or disconnecting the battery restarts the process instead of advancing it.

Question 46General Engine Diagnosis

After battery replacement, a vehicle idles roughly and hunts for several minutes before smoothing out. What best explains this?

  1. The fuel pump lost its prime and is cavitating
  2. The alternator is not charging at idle
  3. The PCM lost its learned idle and fuel adaptive values Correct answer.
  4. The camshaft position sensor needs replacement

Explanation

Adaptive idle and fuel values are held in keep-alive memory, which is lost when battery power is removed. The PCM must relearn them, and the engine runs poorly until it does.

Question 47General Engine Diagnosis

An injector balance test shows one injector with a much smaller pressure drop than the others. What does this indicate?

  1. That injector is restricted and flows less fuel Correct answer.
  2. The fuel pressure regulator has failed
  3. The test was invalid because pressure should rise
  4. That injector is leaking and flows more fuel

Explanation

Each injector is pulsed for the same time, so the pressure drop is proportional to the fuel delivered. A smaller drop means less fuel passed through, which points to a clogged nozzle or inlet screen.

Question 48General Engine Diagnosis

A heated oxygen sensor heater circuit fault is stored for bank 1 sensor 1. Which is the most likely effect on engine operation?

  1. Delayed closed loop entry and slower sensor response Correct answer.
  2. Immediate loss of all fuel control and a no-start
  3. A steady misfire on the affected bank
  4. A continuous rich command because the sensor reads zero

Explanation

The heater brings the sensor to operating temperature quickly, especially at idle and light load when exhaust is cool. Losing it leaves the element cold longer, which delays closed loop and slows response.

Question 49General Engine Diagnosis

An oiled aftermarket air filter contaminates the MAF sensing element. What symptom is most likely?

  1. A constant 5-volt MAF signal at idle
  2. Lean fuel trims because the sensor underreports airflow Correct answer.
  3. No effect because MAF is only used at wide open throttle
  4. Rich fuel trims because the sensor overreports airflow

Explanation

A contaminated hot-wire or hot-film element cannot shed heat correctly and typically underreports airflow. The PCM then calculates too little fuel and long term trim goes positive.

Question 50General Engine Diagnosis

On an electronic throttle vehicle, how should accelerator pedal position sensor signals 1 and 2 behave?

  1. They should both read 5 volts at closed throttle
  2. They should read identical voltages at every position
  3. They should alternate between 0 and 5 volts as the pedal moves
  4. They should track proportionally with one another Correct answer.

Explanation

Redundant APP sensors are built with different slopes or offsets so the PCM can cross-check them against each other. A disagreement outside the calibrated window forces reduced power mode.