ASE Automobile (A1–A8) — All Questions

A knock sensor allows the PCM to:

• a.Read vehicle speed
• b.Control the fuel pump
• c.Measure exhaust oxygen
• d.Detect detonation and retard ignition timing to protect the engine✓

The knock sensor detects the vibration of detonation so the PCM can retard timing and prevent engine damage. Persistent knock can come from low-octane fuel, carbon buildup, or overheating. A faulty sensor may cause reduced performance or a code.

The EVAP system is designed to:

• a.Increase fuel pressure
• b.Cool the intake charge
• c.Filter engine oil
• d.Capture and burn fuel vapors from the tank rather than venting them✓

The evaporative emission system stores fuel vapors in a charcoal canister and later purges them into the intake to be burned, preventing release to the atmosphere. A loose or faulty gas cap is a common cause of small-leak codes. It is tested for leaks during OBD-II monitors.

A loose or missing fuel cap most commonly sets which type of code?

• a.A coolant temperature code
• b.An ABS code
• c.An EVAP system leak code (such as P0455 or P0457)✓
• d.A misfire code

A poorly sealing fuel cap lets vapors escape and triggers an EVAP leak code, often the first thing to check for such faults. Tightening or replacing the cap and clearing the code frequently resolves it. Smoke testing finds larger leaks in the system.

Technician A says low fuel pressure can cause a lean misfire and hesitation. Technician B says a clogged fuel filter or weak pump can lower fuel pressure. Who is correct?

• a.Both A and B✓
• b.Technician A only
• c.Neither A nor B
• d.Technician B only

Insufficient fuel pressure leans the mixture, causing misfire, hesitation, and lack of power, and a restricted filter or failing pump is a common cause. Both technicians are correct. A fuel-pressure test and volume check confirm delivery problems.

The throttle position sensor (TPS) informs the PCM about:

• a.Battery voltage
• b.Coolant level
• c.Exhaust temperature
• d.Throttle plate angle (driver demand)✓

The TPS reports how far the throttle is open so the PCM can adjust fuel, timing, and transmission strategy. A faulty or dead-spot TPS causes hesitation, surging, or erratic shifts. Its signal is checked with a scan tool or by watching voltage sweep.

A vehicle fails an emissions test for high hydrocarbons (HC). This is most commonly associated with:

• a.A worn wheel bearing
• b.Excessive coolant
• c.Low tire pressure
• d.Unburned fuel from misfire, ignition, or rich-condition problems✓

High HC indicates unburned fuel escaping into the exhaust, typically from misfires, ignition faults, or an overly rich mixture. Diagnosing the misfire or fuel-control fault reduces HC. A failing catalytic converter can also raise tailpipe HC.

The PCM uses the crankshaft position sensor primarily to:

• a.Measure intake air temperature
• b.Detect wheel slip
• c.Read exhaust oxygen
• d.Determine engine speed and piston position for ignition and fuel timing✓

The crankshaft position sensor tells the PCM engine rpm and crank position so it can time spark and injection. Loss of this signal usually prevents the engine from starting. A cam/crank correlation code indicates timing has slipped between the two.

On an OBD-II vehicle, the data link connector (DLC) used to retrieve codes is standardized as a:

• a.9-pin round plug under the hood
• b.4-pin trailer connector
• c.16-pin connector, usually under the dash✓
• d.2-pin connector at the battery

OBD-II mandates a standardized 16-pin DLC, typically located under the driver's side dash, for scan-tool access. This standard allows generic tools to read codes and data across manufacturers. Certain pins carry power, ground, and communication signals.

The exhaust gas recirculation (EGR) system reduces which emission by lowering combustion temperature?

• a.Oxides of nitrogen (NOx)✓
• b.Carbon monoxide (CO)
• c.Carbon dioxide (CO2)
• d.Hydrocarbons (HC)

EGR routes inert exhaust gas back into the intake to lower peak combustion temperature, reducing the formation of NOx. A clogged EGR passage can cause knock and high NOx, while a stuck-open valve causes rough idle. Its operation is monitored by OBD-II.

A no-start with no spark and no injector pulse, but a good battery and cranking, most likely points to:

• a.A worn water pump
• b.A leaking A/C condenser
• c.A failed crankshaft position sensor or PCM/power issue✓
• d.A clogged cabin filter

When both spark and injector pulse are absent during cranking, a shared input such as the crankshaft position sensor or a PCM power/ground problem is a prime suspect. Scan-tool rpm during cranking helps confirm the crank signal. Systematic checks of power, ground, and reference sensors isolate the cause.

An outside micrometer is used to measure:

• a.Coolant temperature
• b.Precise outside dimensions such as shaft or rotor thickness✓
• c.Electrical resistance
• d.Torque on a fastener

An outside micrometer measures external dimensions to a thousandth of an inch or finer, such as a rotor or crankshaft journal. The reading combines the sleeve and thimble scales. Proper technique and calibration are essential for accuracy.

A torque wrench is used to:

• a.Measure bore diameter
• b.Tighten fasteners to a specified value✓
• c.Check tire tread depth
• d.Test battery voltage

A torque wrench applies a controlled, specified amount of tightening force so fasteners are neither loose nor overtightened. Proper torque is critical for head bolts, wheels, and many other parts. The wrench should be set back to its lowest setting when stored to preserve calibration.

Technician A says wheel lug nuts can be tightened in any order. Technician B says they should be tightened in a crisscross (star) pattern to the specified torque. Who is correct?

• a.Both A and B
• b.Neither A nor B
• c.Technician B only✓
• d.Technician A only

Lug nuts must be tightened gradually in a crisscross pattern to seat the wheel evenly and prevent rotor distortion. Uneven or over-tightening can warp rotors and damage studs. Technician A is incorrect.

Technician A says a vehicle should be supported at the manufacturer's designated lift points. Technician B says rated jack stands should support a vehicle before working underneath it. Who is correct?

• a.Both A and B✓
• b.Technician A only
• c.Technician B only
• d.Neither A nor B

Vehicles must be supported at designated lift points and secured on rated jack stands, never held only by a hydraulic jack. Both technicians are correct. Following these practices prevents damage and serious injury.

Technician A says a dial indicator measures runout, endplay, and gear backlash. Technician B says it must be set up perpendicular to the surface for an accurate reading. Who is correct?

• a.Both A and B✓
• b.Neither A nor B
• c.Technician B only
• d.Technician A only

A dial indicator measures small linear movements such as rotor runout, crankshaft endplay, and backlash, and the plunger must contact the surface perpendicularly for accuracy. Both technicians are correct. It reads deflection in thousandths of an inch.

A vehicle's service information (repair manual) is the best source for:

• a.Fuel prices
• b.Torque specifications, procedures, and wiring diagrams✓
• c.The owner's phone number
• d.Weather forecasts

Service information provides the manufacturer's specifications, step-by-step procedures, wiring diagrams, and fluid capacities needed for correct repairs. Using accurate data prevents mistakes and comebacks. Technicians should verify specs rather than rely on memory.

If a bolt must be torqued to 90 foot-pounds and the specification then calls for an additional 90-degree turn, this method is known as:

• a.Static balancing
• b.Preloading only
• c.Cross-torquing
• d.Torque-to-yield (torque-plus-angle)✓

Torque-plus-angle (torque-to-yield) tightens the fastener to a base torque and then a specified angle, stretching it for consistent clamp load. It is common on head bolts and other critical fasteners. A torque-angle gauge or electronic tool measures the additional rotation.

Proper personal protective equipment when grinding or working with the battery includes:

• a.Only gloves
• b.Only a hat
• c.Eye protection and appropriate gloves✓
• d.No protection needed

Eye protection guards against flying particles and battery acid, and gloves protect the hands from sharp edges and corrosive chemicals. Battery work also warrants care because of explosive hydrogen gas and acid. Safety equipment reduces the risk of injury.

Converting a measurement, a technician knows there are 25.4 millimeters in one inch. A 2-inch dimension equals approximately:

• a.50.8 mm✓
• b.254 mm
• c.12.7 mm
• d.2.54 mm

Multiplying 2 inches by 25.4 mm/inch gives 50.8 millimeters. Being comfortable converting between metric and standard units is important because vehicles use both. Measuring tools and specifications may be given in either system.

A feeler gauge is used to measure:

• a.The gap or clearance between two parts✓
• b.Tire pressure
• c.Electrical current
• d.Engine vacuum

A feeler gauge consists of thin metal blades of known thickness used to measure small gaps, such as valve lash or spark plug gap. The correct blade slides through the gap with a slight drag. It is a simple but precise clearance-measuring tool.

A valve spring is checked for squareness and free length. A spring shorter than spec or leaning against a square should be:

• a.Reinstalled as-is because free length rarely affects performance
• b.Replaced, because it has lost tension and may allow valve float✓
• c.Restored by heating the spring and re-tempering the metal
• d.Corrected by installing a thicker retainer and keeper set

A spring that has lost free length or is no longer square has weakened and can allow valve float at high rpm, so it must be replaced. Weak springs cause power loss and can let valves bounce off their seats. Both free length and load-at-height are compared to specification.

Blue smoke on startup that clears after a few seconds, with good compression, most often points to:

• a.A stuck-open thermostat that keeps the engine running cold
• b.A leaking fuel injector that floods the cylinder with fuel
• c.A cracked cylinder block allowing coolant into a cylinder
• d.Worn valve stem seals or valve guides letting oil seep in✓

Oil that seeps past worn valve guide seals while the engine sits gets burned at startup, producing brief blue smoke that clears as the guides drain. Compression stays normal because the rings are still sealing. Replacing the valve stem seals usually corrects it.

During a compression test, a low cylinder rises noticeably after squirting oil into it. This indicates the cause is:

• a.A burned or leaking valve that oil cannot seal at all
• b.A cracked piston crown venting compression to the crankcase
• c.A blown head gasket letting pressure escape to coolant
• d.Worn piston rings or cylinder walls that oil temporarily seals✓

Oil temporarily seals worn rings, so a reading that jumps up on the wet test points to ring or cylinder wear rather than a valve. If the reading stays low wet, the leak is at a valve or head gasket. This wet/dry comparison localizes the cause before teardown.

During a cylinder leak-down test, air escapes from the radiator or coolant reservoir. This indicates a leak at the:

• a.Exhaust valve, heard as air hissing from the tailpipe
• b.Head gasket or a cracked head or block✓
• c.Piston rings
• d.Intake valve

Air heard bubbling in the cooling system during leak-down means combustion pressure is reaching a coolant passage, pointing to a failed head gasket or crack. Air from the intake indicates an intake valve, from the exhaust an exhaust valve, and from the oil filler indicates rings. Where the air escapes tells you where the leak is.

One cylinder is weak and a worn camshaft lobe is suspected. Lobe wear reduces that cylinder's power because it:

• a.Increases oil pressure to that cylinder head
• b.Raises the compression ratio far above the other cylinders
• c.Decreases valve lift and duration on that cylinder✓
• d.Advances the ignition timing only on the affected cylinder

A rounded-off cam lobe opens its valve less far and for less time, reducing airflow and power on that cylinder. Flat-tappet cams are especially prone to lobe wear. Measuring valve lift at the retainer or comparing lobes confirms it.

Technician A says a noisy hydraulic lifter can be caused by low oil pressure or aerated oil. Technician B says a collapsed lifter can hold a valve open and cause a misfire. Who is correct?

• a.Technician B only
• b.Technician A only
• c.Neither A nor B
• d.Both A and B✓

Hydraulic lifters rely on clean, pressurized oil, so low pressure or air makes them clatter, and a lifter that bleeds down can affect valve action and cause a misfire. Both technicians are correct. Clean oil at the correct level and pressure keeps lifters quiet.

When installing a cylinder head, the head bolts should be tightened:

• a.Only by feel with an impact gun rather than a torque wrench
• b.From one corner straight across to the opposite corner in a single pass
• c.To full final torque in random order to save time on the job
• d.Gradually in the specified sequence, usually center outward✓

Tightening in the manufacturer's sequence, typically working outward from the center in stages, distributes clamp load evenly and prevents warping the head or crushing the gasket. Skipping the sequence causes leaks. Many heads use a torque-plus-angle procedure with new bolts.

An engine overheats only at idle or in slow traffic but cools at highway speed. The MOST likely cause is:

• a.A stuck-closed thermostat
• b.A worn timing chain
• c.An inoperative cooling fan or fan clutch✓
• d.A collapsed lower radiator hose starving the pump

At speed, ram air cools the radiator, but at idle the electric fan or fan clutch must move the air; if it fails, the engine overheats when stopped. A stuck thermostat overheats at all speeds. Verifying fan operation is the first check for this pattern.

Coolant dripping from the weep hole under the water pump, with a bearing whine, indicates:

• a.A failing water pump seal and bearing✓
• b.A cracked overflow bottle losing coolant onto the ground
• c.A bad radiator cap
• d.A leaking heater core

The weep hole is designed to leak when the internal pump seal fails, protecting the bearing from coolant; leakage plus noise means the pump is worn out. Continued use risks pump seizure and belt or timing damage. Replacing the pump and inspecting the belt corrects it.

A serpentine belt that squeals on acceleration and shows a glazed underside most likely needs:

• a.A permanent coating of belt dressing to quiet the squeal
• b.A belt one size wider than specified
• c.The tensioner removed entirely
• d.A new belt plus inspection of the automatic tensioner✓

Glazing and squeal indicate belt wear or a weak tensioner that no longer maintains proper tension, so the belt should be replaced and the tensioner checked. A worn tensioner spring lets the belt slip. Belt dressing only masks the problem temporarily.

A 50/50 mix of antifreeze and water is used instead of straight antifreeze mainly because the mix provides:

• a.Extra lubrication for the water pump
• b.A higher freezing point than a mixture containing water
• c.Better heat transfer with freeze and boil protection✓
• d.A lower material cost

Water transfers heat better than pure antifreeze, so a balanced mix cools effectively while still protecting against freezing, boiling, and corrosion. Straight antifreeze actually transfers heat poorly and can raise operating temperature. The correct ratio and coolant type matter for protection.

All of the following can cause an engine to overheat EXCEPT:

• a.A thermostat stuck closed
• b.A low coolant level or an airlock
• c.A radiator restricted or clogged with scale, debris, or bugs
• d.An overcharged air conditioning refrigerant system✓

Overheating comes from anything that blocks heat rejection or coolant flow, such as a stuck thermostat, low coolant, or a clogged radiator; an A/C overcharge does not directly overheat the engine coolant. Diagnosis follows coolant flow and airflow. The A/C system is a separate refrigerant circuit.

The bypass valve built into or around an oil filter is designed to:

• a.Drain oil out of the filter when the engine is shut off and cools
• b.Permanently increase oil pressure at operating speed
• c.Regulate coolant temperature by routing oil to the cooler
• d.Let oil bypass a clogged filter so parts still get oil✓

If the filter media becomes plugged, the bypass valve opens so unfiltered oil still reaches the bearings rather than starving them. Dirty oil is better than none for short-term protection. Regular oil changes prevent the filter from clogging in the first place.

In the oil rating 5W-30, the '5W' refers to the oil's:

• a.Detergent and dispersant strength
• b.Percentage of the additive package
• c.Cold-temperature (winter) flow characteristics✓
• d.Operating oil pressure the engine develops at idle

In a multi-viscosity oil, the number before the W describes flow when cold for easier starting, while the second number describes viscosity at operating temperature. A lower W number flows better in the cold. Using the specified grade protects the engine across the temperature range.

Crankshaft endplay is measured with a dial indicator by prying the crank fore and aft. Excessive endplay indicates a worn:

• a.Main bearing
• b.Thrust bearing✓
• c.Camshaft bearing
• d.Connecting-rod bearing

The thrust bearing controls the crankshaft's front-to-back movement, so excessive endplay points to thrust bearing wear. Too much endplay can cause a knock and disturb the crank sensor or converter. It is checked with a dial indicator against the crank snout.

A deep knock present at idle that worsens with load, following recent low oil pressure, most likely indicates:

• a.A slipping accessory drive belt riding on a seized pulley
• b.A worn crankshaft bearing damaged by oil starvation✓
• c.A sticking EGR valve
• d.A loose spark plug

Loss of oil film from low pressure damages the crankshaft bearings, producing a load-sensitive knock. A rod bearing knock is often quieted by disabling that cylinder, while a main bearing knock is a heavier, lower thump. Confirming oil pressure and inspecting bearings is required.

When installing piston rings, the ring end gaps should be:

• a.Aligned directly over the wrist pin so the gaps share a common axis
• b.Staggered around the piston, not aligned with each other✓
• c.Positioned all together on the thrust side of the piston skirt
• d.Butted tightly together with essentially zero end-gap clearance

Staggering the end gaps keeps combustion pressure from blowing straight down through aligned gaps, reducing blow-by and oil consumption. The correct end gap clearance is also checked in the bore with a feeler gauge. Aligned gaps cause smoking and pressure loss.

A light knocking or slapping noise loudest on a cold start that quiets as the engine warms most likely indicates:

• a.A leaking head gasket letting gases into the cooling system
• b.A clogged catalytic converter
• c.Piston slap from excessive piston-to-wall clearance✓
• d.A worn water pump bearing that is noisy only once warm

Piston slap occurs when a worn piston rocks in the bore while cold, and it quiets as the piston expands with heat. It is usually not immediately harmful but indicates cylinder wear. A cracked piston skirt can produce a similar cold noise.

A ticking noise loudest when the engine is cold that diminishes as it warms, near the exhaust, often indicates:

• a.A slipping timing chain that has jumped teeth on the sprocket
• b.A cracked exhaust manifold or a leaking manifold gasket✓
• c.A worn crankshaft main bearing
• d.A failing oil pump

A cracked manifold or leaking gasket ticks when cold because the gap is largest before the metal expands and closes it with heat. The sound is a rhythmic exhaust tick. Inspection and a leak test confirm the crack.

A vacuum gauge on the intake shows a steady but low reading (about 12 in-Hg) at idle. This most commonly indicates:

• a.A single burned valve, which drops the needle rhythmically
• b.Excessive oil pressure transmitted through the intake manifold
• c.Retarded ignition or valve timing, or a vacuum leak✓
• d.A perfectly healthy engine

A steady low vacuum reading points to late timing or a general leak rather than a single-cylinder fault, which would make the needle drop rhythmically. Vacuum testing is a quick way to gauge engine condition. Comparing the pattern to known signatures guides diagnosis.

A core (freeze) plug leaking coolant on the side of the block should be:

• a.Replaced with a new plug and sealer✓
• b.Ground off flush with the block and left open
• c.Sealed temporarily with tape
• d.Left alone if the leak is small and slow

A corroded or pushed-out core plug leaks coolant and must be replaced, since it is a sealed opening left from casting. Coolant loss leads to overheating. The new plug is installed with sealer and driven in squarely.

On an interference engine, a broken timing belt will most likely cause:

• a.A sudden increase in oil pressure as the camshaft stops
• b.A slipping clutch
• c.Only a no-start with no internal damage
• d.Valve-to-piston contact and internal engine damage✓

In an interference design the valves and pistons share the same space at different times, so a broken belt lets them collide, bending valves or worse. This is why timing belts have strict replacement intervals. A non-interference engine simply stops without contact.

Valve lash adjusted too tight (too little clearance) on a solid-lifter engine can cause:

• a.Increased oil consumption from oil pulled past the guides
• b.A burned valve from being held slightly off its seat✓
• c.Higher oil pressure because the lifters bleed down slowly
• d.Excessive valvetrain noise

Too little clearance can hold a valve off its seat as the engine heats and parts expand, preventing the valve from cooling through the seat and burning it. Too much lash instead causes noise. Correct lash allows full seating and heat transfer.

Cylinder head flatness (warp) is checked with a:

• a.Compression tester
• b.Vacuum gauge
• c.Dial bore gauge set to each cylinder's diameter
• d.Straightedge and feeler gauge across the deck✓

A precision straightedge laid across the head with a feeler gauge slipped underneath reveals warp beyond the flatness limit. Excess warp requires resurfacing. This check is done in several directions across the deck.

With a rocker arm ratio of 1.6:1 and a cam lobe lift of 0.300 inch, the valve lift is approximately:

• a.1.600 inch
• b.0.300 inch
• c.0.188 inch
• d.0.480 inch✓

Rocker arm ratio multiplies lobe lift, so 0.300 inch times 1.6 equals 0.480 inch of valve lift. The rocker acts as a lever to increase lift at the valve. Understanding the ratio matters when comparing cam specs and valve movement.

A voltmeter with one lead in the coolant and one on the battery negative reads a high DC voltage. This indicates:

• a.A perfectly normal cooling system with fresh coolant inside
• b.Electrolysis that can corrode cooling-system metals✓
• c.A thermostat stuck closed
• d.A weak battery needing replacement

Stray current through the coolant, often from a poor engine ground, creates electrolysis that eats away radiators, heater cores, and pump parts. Fresh coolant with intact inhibitors and good grounds keep it low. A high reading calls for finding the ground fault.

A chemical block tester (combustion leak test) checks for a head gasket leak by detecting combustion gases in the:

• a.Coolant, shown by a color change in the test fluid✓
• b.Intake manifold, measured as a change in idle vacuum
• c.Exhaust stream, as a rise in backpressure
• d.Engine oil, measured by comparing hot and cold viscosity

The block tester draws air from the coolant reservoir through a blue fluid that turns yellow if combustion gases are present, confirming a head gasket or crack. It detects hydrocarbons that should never reach the coolant. It is a quick, non-invasive test.

Detonation (spark knock) differs from pre-ignition in that detonation is:

• a.A condition caused only by an excessively rich air-fuel mixture
• b.Uncontrolled combustion after the spark collides with the flame✓
• c.Combustion that begins before the spark plug fires from a hot spot
• d.A completely normal combustion event that occurs at every idle

Detonation is a secondary autoignition after the plug fires, whose pressure spikes collide with the normal flame and cause the knock, while pre-ignition ignites before the spark from a hot spot. Both can damage pistons. Low octane, carbon, lean mixtures, and overheating promote knock.

Thick, dark sludge found throughout an engine is most commonly the result of:

• a.Frequent long highway trips
• b.Neglected oil changes and extended drain intervals✓
• c.Installing a fresh oil filter at every scheduled service
• d.Using a full-synthetic oil

Sludge forms when oil oxidizes and collects contaminants because it was not changed on schedule, clogging passages and starving parts. Short trips and skipped services accelerate it. Regular changes with the correct oil prevent sludge.

The oil pressure relief valve in the lubrication system:

• a.Cools the oil by routing it through a heat exchanger in the pan
• b.Limits peak oil pressure by returning excess oil to the pan✓
• c.Increases oil pressure without limit as engine speed keeps rising
• d.Filters contaminants out of the oil before it reaches the bearings

The relief valve opens when pressure exceeds a set point, bleeding oil back to the sump so the system is not over-pressurized. A stuck valve can cause abnormally high or low pressure. It protects seals, the filter, and galleries.