ASE Automobile (A1–A8) — All Questions

Torque steer, a pull under hard acceleration on a front-wheel-drive car, is most associated with:

• a.A worn brake master cylinder leaking fluid past its internal seals
• b.Unequal drive axle angles or lengths applying torque unevenly✓
• c.A dirty engine air filter restricting airflow into the intake tract
• d.A leaking A/C evaporator dripping refrigerant oil in the HVAC case

Torque steer arises when the front drive axles apply torque unevenly, often due to their differing angles or lengths, pulling the steering during acceleration. Worn mounts or suspension parts can worsen it. It is distinguished from an alignment pull by its throttle sensitivity.

Excessive positive caster on a vehicle without power steering will most noticeably increase:

• a.The vehicle's tendency to wander and drift at highway speed
• b.The likelihood that the wheels will shimmy at a specific speed
• c.Steering effort while improving straight-line stability✓
• d.Tire wear across the center of the tread on both front tires

Positive caster tilts the steering axis rearward at the top, aiding stability and return but raising effort, which is more noticeable without power assist. Too little caster causes wander instead. Caster is compared side to side during alignment.

Technician A says a worn ball joint can produce a clunk and cause a failed alignment. Technician B says a worn ball joint can wear a tire and, if it separates, cause loss of control. Who is correct?

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

A worn ball joint clunks, shifts alignment, wears tires, and can fail dangerously if it separates. Both technicians are correct. Worn joints are replaced before performing an alignment.

Technician A says correct toe is critical for even tire wear. Technician B says toe is adjustable on most vehicles. Who is correct?

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

Toe strongly affects tire wear and is adjustable on virtually all vehicles. Both technicians are correct. Toe is typically the last angle set during an alignment.

Technician A says a defective (conicity) tire can cause a pull. Technician B says swapping the front tires side to side can help confirm a tire-caused pull. Who is correct?

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

A tire with internal conicity can steer the vehicle, and swapping the tires side to side changes or moves the pull, confirming the tire. Both technicians are correct. This test isolates a tire pull from an alignment pull.

R-1234yf, used in newer vehicles instead of R-134a, is notable because it:

• a.Is chemically identical to the older R-12 refrigerant it replaced
• b.Can be freely mixed with R-134a in any proportion without a problem
• c.Requires no special handling, fittings, or recovery equipment at all
• d.Has a much lower global-warming impact and is mildly flammable✓

R-1234yf was adopted for its low global-warming potential, but it is mildly flammable and must not be mixed with other refrigerants. It uses unique fittings and equipment to prevent cross-contamination. Correct identification and handling are required.

The high-side and low-side service ports on a modern A/C system use different fitting sizes so that:

• a.Refrigerant is able to flow through the system faster
• b.Equipment cannot be connected to the wrong side✓
• c.The compressor runs at a cooler temperature under heavy load
• d.Compressor oil is added automatically

Different quick-couple sizes on the high and low sides prevent connecting the manifold set or charging equipment backward. This protects the technician and the system. The ports are also marked H and L.

A manifold gauge set connected to an A/C system is used to:

• a.Check the tread depth on each tire
• b.Test the battery's voltage and cold-cranking performance
• c.Read high- and low-side pressures for diagnosis✓
• d.Measure engine oil pressure at idle

The manifold gauges show both system pressures, which the technician interprets to judge charge level, restrictions, and component operation. It also controls evacuation and charging. Pressure readings are compared with ambient temperature.

Before recharging an A/C system that has been opened, the system should be:

• a.Pressurized with ordinary compressed shop air to check for leaks
• b.Evacuated with a vacuum pump to remove air and moisture✓
• c.Placed in a freezer overnight
• d.Filled quickly with refrigerant without pulling any vacuum

Pulling a deep vacuum removes non-condensable air and lowers the boiling point of any moisture so it evaporates and is drawn out. Moisture left inside forms acids and ice. A proper evacuation precedes charging by weight.

Using the wrong or incompatible compressor oil in an A/C system can cause:

• a.Poor lubrication and compressor damage✓
• b.A stronger and hotter cabin heater output
• c.A faster windshield defrost
• d.A noticeable increase in overall highway fuel economy

A/C compressors require the specific oil type for their refrigerant; the wrong or contaminated oil breaks down lubrication and can destroy the compressor. PAG and POE oils are matched to system requirements. The correct oil and amount are specified by the manufacturer.

The air gap on a magnetic A/C compressor clutch is important because:

• a.It controls the blower speed set on the HVAC control head
• b.Too large a gap can keep the clutch from engaging✓
• c.It cools the condenser
• d.It sets the refrigerant charge weight

The clutch engages when the coil pulls the plate across the air gap; if the gap grows too wide, the clutch slips or will not engage. The gap is measured and shimmed to spec. A worn or improperly gapped clutch causes intermittent cooling.

A low-pressure cutout switch in an A/C system protects the compressor by:

• a.Adding more refrigerant into the system automatically when low
• b.Opening the blend-air door over the core
• c.Disengaging the clutch when pressure or charge is too low✓
• d.Increasing the blower speed across the coils

If the charge drops too low, the low-pressure switch cuts the clutch so the compressor is not run without adequate refrigerant and oil circulation. This prevents damage from lack of lubrication. It is a common reason a clutch will not engage.

A high-pressure cutout switch is used to:

• a.Charge the vehicle's battery through the air conditioning system
• b.Shut off the compressor if pressure rises dangerously high✓
• c.Boost the output of the cabin heater when the engine is fully warm
• d.Regulate the flow of engine coolant through the heater core

The high-pressure switch or transducer disengages the clutch or signals the module when pressures climb too high, protecting components from a blocked condenser or overcharge. It works with the fan controls to manage pressure. Excess pressure can rupture parts if unchecked.

In an orifice tube (CCOT) A/C system, the accumulator is located:

• a.On the high-pressure liquid line, before the condenser inlet
• b.Inside the compressor housing
• c.Within the heater core assembly
• d.On the low-pressure suction side, after the evaporator✓

The accumulator sits on the suction line in orifice-tube systems to store excess refrigerant and protect the compressor from liquid slugging, and it holds desiccant. A receiver-drier, by contrast, is used on the liquid line of expansion-valve systems. Its location matches the metering device type.

The receiver-drier in a thermostatic expansion valve (TXV) system is located:

• a.Inside the blower motor housing on the passenger side of the case
• b.On the low-pressure suction line just after the evaporator outlet
• c.On the high-pressure liquid line, before the expansion valve✓
• d.Within the radiator core alongside the engine coolant passages

The receiver-drier stores liquid refrigerant and removes moisture on the high side ahead of the TXV, ensuring only liquid reaches the valve. Orifice-tube systems instead use a suction-side accumulator. Matching the component to the system type is important during service.

An evaporator that repeatedly freezes over, cutting off airflow, is often caused by:

• a.A control that fails to cycle the compressor off in time✓
• b.A leaking axle seal letting gear oil reach the brake linings
• c.A worn front wheel bearing that drones and roughens with speed
• d.A cracked engine exhaust manifold ticking loudly on a cold start

If the compressor does not cycle off as the evaporator nears freezing, condensation freezes on the fins and blocks airflow. A thermostat, temperature sensor, or pressure switch normally prevents this. Restoring proper cycling stops the icing.

A blower motor that works only on the highest speed, with lower speeds dead, most likely has:

• a.A stuck blend-air door leaving vent temperature uncontrollable
• b.A clogged orifice tube
• c.A low refrigerant charge
• d.A failed blower motor resistor or speed control module✓

The resistor pack or solid-state control sets the lower fan speeds, so its failure often leaves only high speed working, which bypasses the resistor. Replacing the resistor or module restores all speeds. A blower that does not run at all points elsewhere.

A stuck blend-air door actuator will most likely cause:

• a.A dead battery after the vehicle sits overnight
• b.A refrigerant leak from the low side that empties the system
• c.A brake pull to one side
• d.Incorrect or uncontrollable vent temperature✓

The blend door meters air across the heater core to set temperature, so a stuck actuator leaves the output stuck hot, cold, or unresponsive to the controls. Actuators can be tested and recalibrated or replaced. Clicking noises often signal a failing actuator.

A dirty or clogged cabin air filter most commonly causes:

• a.Reduced airflow from the dashboard vents✓
• b.A compressor clutch that will not release
• c.A high-side pressure spike
• d.A refrigerant overcharge

A restricted cabin filter chokes the air the blower can move, so vent output drops even though the system is otherwise fine. Replacing the filter restores airflow. It also affects both heating and cooling volume.

An A/C performance test is typically evaluated by measuring the:

• a.Engine oil pressure at idle and again at normal operating speed
• b.Battery cold-cranking amps under load with a carbon-pile tester
• c.Vent discharge air temperature plus the system pressures✓
• d.Tire tread depth at several points across each of the four tires

Technicians judge A/C performance by the temperature at the center vent, together with high- and low-side pressures at a known ambient temperature and humidity. These readings reveal charge and component problems. Manufacturer specs give the target vent temperature.

A very low low-side pressure with frost forming at the metering device inlet usually indicates:

• a.A restriction at the orifice tube or expansion valve✓
• b.A worn front wheel bearing
• c.An overcharge of refrigerant that raises both service pressures
• d.A slipping serpentine belt

A blockage at the orifice or a stuck-closed expansion valve starves the evaporator, dropping low-side pressure and causing localized frost from the pressure drop at the restriction. Cooling suffers because little refrigerant flows. Replacing the metering device or clearing the restriction restores flow.

In a system with a heater control valve, no cabin heat could be caused by the valve being:

• a.Frozen solid by the cold evaporator core mounted next to it
• b.Stuck wide open and sending too much refrigerant into the evaporator
• c.Electrically bypassed by the blower motor speed control resistor
• d.Stuck closed and blocking coolant to the heater core✓

A heater control valve regulates hot coolant to the core; if it sticks closed, no hot coolant reaches the core and there is no heat. A stuck-open valve can make heat hard to shut off. Not all vehicles use such a valve, relying on the blend door instead.

No cabin heat with the engine at normal temperature and a full cooling system is often caused by a:

• a.Low refrigerant charge
• b.Clogged heater core or a stuck blend-air door✓
• c.Worn compressor clutch that slips on its pulley
• d.Faulty high-pressure cutout switch

With the engine warm and coolant full, a lack of heat points to restricted coolant flow through the core or a blend door not directing air over it. Flushing the core or repairing the actuator restores heat. Refrigerant components affect cooling, not heating.

In an automatic climate control system, the in-car temperature sensor is used to:

• a.Measure refrigerant pressure on the high and low sides of the system
• b.Provide feedback so the system holds the set temperature✓
• c.Read the wheel speeds for traction control
• d.Sense the engine oil level

The in-car sensor tells the module the actual cabin temperature so it can adjust blend, blower, and compressor to hold the setpoint. A faulty or blocked sensor causes poor temperature control. A small aspirator fan often draws air across it.

Refrigerant leaks are commonly located using:

• a.An electronic leak detector or UV dye with a UV light✓
• b.A test light probed across the battery's positive terminal
• c.A compression tester threaded into each spark plug hole
• d.A vacuum gauge on the intake manifold

An electronic sniffer or fluorescent dye traced with a UV lamp pinpoints where refrigerant is escaping. The leak must be repaired before recharging. Soap solution can help confirm a suspected spot.

Severe internal compressor failure that spreads metal debris through the system requires:

• a.Flushing or replacing contaminated parts and adding a filter✓
• b.Replacing only the cabin air filter
• c.Only adding a larger amount of fresh refrigerant to flush it out
• d.Raising the idle to spin the new compressor faster

When a compressor comes apart, debris and acid contaminate the system, so the affected parts are flushed or replaced and an inline filter is often added to protect the new compressor. Simply installing a compressor invites repeat failure. Proper cleanup and oil balancing are essential.

The condenser cooling fan should run when the A/C is on because it:

• a.Cools the front brake rotors during repeated hard braking
• b.Charges the vehicle's battery whenever the engine runs
• c.Provides airflow so the condenser can reject heat✓
• d.Increases fuel pressure at the injectors

The condenser needs airflow to condense the refrigerant; at idle or low speed the electric fan supplies it, so a fan failure raises high-side pressure and hurts cooling. The module commands the fan based on A/C and pressure inputs. Verifying fan operation is part of A/C diagnosis.

High high-side pressure with normal or low low-side pressure and poor cooling often indicates:

• a.A worn tie rod end
• b.A low refrigerant charge reading low on both gauges
• c.A condenser airflow problem or a system overcharge✓
• d.Air trapped in a hydraulic brake line

Restricted condenser airflow, from a blocked condenser or a dead fan, or an overcharge, raises high-side pressure and reduces cooling. Verifying fan operation, condenser cleanliness, and charge weight isolates it. Correcting airflow or charge normalizes pressures.

Before recovering refrigerant from an unknown system, a technician should:

• a.Add fresh compressor oil to the system
• b.Disconnect the vehicle battery
• c.Run the engine at full throttle to warm the refrigerant first
• d.Check it with a refrigerant identifier for contamination✓

A refrigerant identifier verifies the type and purity so contaminated or mixed refrigerant is not pulled into the shop's clean recovery tank. Cross-contamination ruins equipment and refrigerant. This check protects the machine and future jobs.

An A/C compressor clutch that stays engaged and will not disengage could be caused by a:

• a.Low refrigerant charge
• b.Clogged orifice tube starving the evaporator of refrigerant
• c.Stuck (welded) clutch relay or a control-circuit fault✓
• d.Torn cabin air filter

A relay with welded contacts or a shorted control circuit can keep power on the clutch coil so it never releases. Checking the relay and control signal isolates it. A clutch that never disengages can overcool or overwork the system.

A musty or moldy smell when the A/C first turns on is most often caused by:

• a.Microbial growth on the damp evaporator, often from a blocked drain✓
• b.A refrigerant overcharge that raises pressure on both service gauges
• c.A cracked condenser leaking refrigerant into the airflow at the front
• d.A worn compressor clutch that slips under load and cannot engage

Moisture condensing on the cold evaporator can grow mold, producing a musty odor, especially if the condensate drain is blocked and water pools. Cleaning or treating the evaporator and clearing the drain helps. Running the fan to dry the core before shutdown reduces it.

Charging an A/C system by weight (the specified amount) is preferred over charging by pressure because it:

• a.Is required only on older R-12 systems
• b.Gives the exact correct charge regardless of conditions✓
• c.Lets the technician ignore the system's rated refrigerant capacity
• d.Uses far less service equipment

The manufacturer specifies an exact refrigerant weight, and charging to that weight avoids the errors of estimating by pressure, which varies with temperature and humidity. Precise charge maximizes cooling and protects the compressor. A recovery/recharge machine measures the charge accurately.

A cracked or leaking heater core will typically produce:

• a.A refrigerant leak from the low side with warm vents
• b.A sweet smell, foggy windows, and coolant loss✓
• c.A high, hard brake pedal
• d.An overcharged battery

Coolant leaking from the heater core inside the dash fogs the glass with a sweet-smelling film and slowly drops the coolant level. The core is pressure-tested and replaced. A greasy film on the windshield is a classic sign.

The mode (air distribution) doors in the HVAC case control:

• a.Whether air comes from the dash, floor, or defrost outlets✓
• b.The temperature of the engine coolant flowing to the heater core
• c.The exact refrigerant charge weight held within the A/C system
• d.The alternator output that charges the battery while driving

Mode doors direct the conditioned air to the panel, floor, defrost, or a blend of outlets as selected. A stuck mode door or actuator leaves airflow at the wrong vents. They are separate from the blend (temperature) door.

Selecting recirculation mode on the HVAC controls causes the system to:

• a.Add more refrigerant into the system to lower the vent temperature
• b.Draw air from inside the cabin rather than from outside✓
• c.Route the incoming air around the evaporator, bypassing the coil
• d.Increase the engine's idle speed to spin the compressor faster

Recirculation closes the fresh-air door and reuses cabin air, which cools faster on hot days and blocks outside odors. A stuck recirculation door can cause weak defrost or stale air. Fresh-air mode brings in outside air for ventilation and defrosting.

A blower motor that does not run at any speed, with a good fuse, most likely has a:

• a.Failed motor, connector, or control switch or module✓
• b.Stuck expansion valve starving the evaporator of refrigerant
• c.Low refrigerant charge
• d.Clogged condenser restricting airflow

No operation at any speed points to the motor itself, its wiring/connector, or the control circuit rather than the resistor, which affects only lower speeds. Power, ground, and control signal are checked at the motor. A common failure is the motor or a burned connector.

A refrigerant identifier is connected before recovery mainly to protect the shop's:

• a.Recovery machine and refrigerant supply from contamination✓
• b.Engine oil supply from being diluted by refrigerant during the process
• c.Battery charger from an electrical overload while the system runs
• d.Brake fluid reservoir from absorbing moisture out of the humid air

Identifying the refrigerant first prevents pulling sealants, air, or mixed refrigerants into the clean recovery tank and machine. Contamination can ruin the equipment and the recovered supply. It is a quick check that safeguards costly gear.

Technician A says an overcharged A/C system can raise high-side pressure and reduce cooling. Technician B says inadequate condenser airflow can do the same. Who is correct?

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

Both an overcharge and poor condenser airflow drive up high-side pressure and hurt cooling. Both technicians are correct. Verifying charge weight and fan operation separates the two causes.

Technician A says refrigerant must be recovered rather than vented. Technician B says a technician handling refrigerant must be certified. Who is correct?

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

Regulations require recovering refrigerant with approved equipment and having certified personnel handle it. Both technicians are correct. This protects the environment and ensures proper service.

Technician A says a low refrigerant charge shows low readings on both gauges. Technician B says any leak should be repaired before recharging. Who is correct?

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

An undercharge reads low on both sides with weak cooling, and the leak must be fixed before recharging by weight. Both technicians are correct. Dye or an electronic detector locates the leak.

A spark plug removed from one cylinder is dry and coated with dry, black soot, while the others are tan. This most directly indicates that cylinder is running:

• a.lean, with excess air scrubbing the insulator clean
• b.cooler than the others because coolant leaked into it
• c.rich, with more fuel than can be fully burned✓
• d.exactly at the stoichiometric ratio

Dry, black, sooty carbon on the insulator points to an over-rich mixture in that cylinder, such as a leaking injector or a fault pulling fuel trim positive there. A tan or light-gray insulator is normal. Wet black deposits instead suggest oil, and white blistering suggests overheating.

The heat range of a spark plug refers to how quickly the plug:

• a.can produce a spark once the ignition module has energized the coil
• b.raises the temperature of the incoming air-fuel charge before ignition
• c.develops secondary voltage across its electrode gap under heavy load
• d.transfers combustion heat away from its firing tip to the cylinder head✓

Heat range describes the plug's ability to conduct heat from the tip into the head. A colder plug sheds heat faster and resists pre-ignition in hot engines, while a hotter plug runs the tip warmer to burn off deposits. Using the specified heat range prevents fouling or detonation.

Spark knock (detonation) heard as a metallic pinging under acceleration can be caused by all of the following EXCEPT:

• a.carbon deposits that raise effective compression
• b.a spark plug gap set slightly wider than specification✓
• c.excessive ignition timing advanced too far for the fuel
• d.fuel with an octane rating below what the engine requires

Detonation is uncontrolled combustion after the spark, driven by too much timing, low octane, carbon buildup, overheating, or a lean mixture. A slightly wide plug gap affects spark, not the pressure-and-temperature conditions that cause knock. The knock sensor retards timing to protect the engine.

An ignition coil steps 12 volts up to the tens of thousands of volts needed to fire the plug primarily because of:

• a.the resistance built into the spark plug wire
• b.the frequency at which the crank sensor triggers the module
• c.the turns ratio between its primary and secondary windings✓
• d.the size of the spark plug electrode gap

A coil is a transformer: the large turns ratio between the many secondary windings and the few primary windings multiplies the induced voltage when the primary field collapses. This produces the high secondary voltage that jumps the plug gap. Weak primary current lowers available secondary voltage.

In a port fuel-injection system, the quantity of fuel delivered by each injector is controlled mainly by the:

• a.diameter of the fuel return line carrying excess fuel to the tank
• b.length of time (pulse width) the PCM holds the injector open✓
• c.spring pressure inside the fuel pressure regulator
• d.resistance printed on the injector's connector

With fuel pressure held relatively constant, the PCM meters fuel by varying injector on-time, called pulse width. Longer pulse width delivers more fuel for acceleration or enrichment. Fuel trims adjust pulse width to keep the mixture near stoichiometric.

Technician A says a clogged or restricted fuel injector can cause a lean misfire on that cylinder. Technician B says a leaking injector can cause a rich condition and hard starting. Who is correct?

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

A restricted injector starves its cylinder and causes a lean misfire, while a leaking injector adds extra fuel that riches the mixture and can flood a cylinder on start-up. Both technicians are correct. An injector balance test compares delivery among cylinders.

The theoretically ideal (stoichiometric) air-fuel ratio for a gasoline engine is approximately:

• a.14.7 parts air to 1 part fuel by weight✓
• b.stoichiometry applies only to diesel engines
• c.1 part air to 14.7 parts fuel by weight
• d.about 9.0 parts air to 1 part fuel

Stoichiometric combustion of gasoline occurs near 14.7:1 air to fuel by mass, the ratio at which the three-way catalyst works most efficiently. The PCM uses oxygen-sensor feedback to hold the average close to this value. Richer or leaner operation is used only for specific conditions.

When the engine is cold at start-up, the PCM operates in open loop, meaning it:

• a.shuts off all of the fuel injectors completely until the engine warms up
• b.doubles the ignition timing advance in order to speed up the warm-up
• c.relies only on the downstream oxygen sensor to control the fuel mixture
• d.ignores the oxygen sensor and uses programmed values to set fuel delivery✓

In open loop the oxygen sensors are not yet at operating temperature, so the PCM meters fuel from stored maps based on coolant temperature, load, and rpm. Once the sensors are hot and the engine is warm, it enters closed loop and trims fuel from sensor feedback.

Short-term fuel trim (STFT) differs from long-term fuel trim (LTFT) in that STFT:

• a.controls ignition timing advance and retard rather than fuel delivery
• b.makes rapid, moment-to-moment corrections from oxygen-sensor feedback✓
• c.is calculated only from the mass airflow reading with no feedback loop
• d.is a permanent stored value that can only be cleared with a scan tool

Short-term fuel trim reacts instantly to oxygen-sensor switching, while long-term fuel trim is a learned, slower average that offsets persistent deviations. Reading both together helps distinguish momentary from ongoing mixture problems. Large positive trims indicate the PCM is adding fuel to correct lean operation.

A manifold absolute pressure (MAP) sensor provides the PCM with information about:

• a.engine load, based on intake manifold pressure and vacuum✓
• b.the mass of air flowing past a heated sensing element in the intake
• c.the rotational position of the camshaft
• d.the oxygen left in the exhaust

A MAP sensor reports manifold pressure, which reflects engine load in a speed-density fuel strategy. High vacuum (low pressure) indicates light load, while low vacuum (near atmospheric) indicates heavy load. A faulty MAP signal skews fuel and timing calculations.