ASE Automobile (A1–A8) — All Questions

The main function of an anti-lock brake system (ABS) is to:

• a.Eliminate the need for brake pads
• b.Replace the parking brake
• c.Prevent wheel lockup and maintain steering control during hard braking✓
• d.Increase brake fluid pressure permanently

ABS pulses hydraulic pressure to keep wheels from locking so the driver retains steering control and shortens stopping distance on most surfaces. Wheel-speed sensors feed the control module, which modulates the hydraulic unit. A fault typically turns on the ABS warning lamp and disables the function.

A wheel-speed sensor signal that is missing on one wheel will most likely cause the ABS to:

• a.Lock all four wheels
• b.Increase engine power
• c.Set a code and disable ABS, reverting to normal braking✓
• d.Apply the parking brake

A lost wheel-speed signal sets a DTC and usually disables ABS, leaving conventional (non-anti-lock) braking available. The ABS warning lamp illuminates. Common causes include a damaged sensor, wiring, or a contaminated tone ring.

Brake fluid is hygroscopic, which means it:

• a.Repels all water
• b.Absorbs moisture from the air over time✓
• c.Expands when frozen
• d.Conducts electricity

Glycol-based brake fluid absorbs moisture, which lowers its boiling point and can cause corrosion and a spongy pedal from vapor under heavy braking. This is why periodic fluid replacement is recommended. Sealed containers and prompt cap replacement limit moisture uptake.

During a disc brake job, a technician should measure rotor thickness and compare it to the:

• a.Toe specification
• b.Tire pressure specification
• c.Minimum (discard) thickness stamped on the rotor✓
• d.Battery voltage

Rotors must remain above the minimum thickness (often cast or stamped on the rotor) to dissipate heat and resist warping. A rotor below spec must be replaced, not machined. Measuring with a micrometer at several points also reveals thickness variation.

Technician A says brake shoes are used in disc brakes. Technician B says brake shoes are used in drum brakes. Who is correct?

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

Drum brakes use curved shoes that press outward against the drum, while disc brakes use flat pads that clamp a rotor. Technician B is correct. Many vehicles combine front discs with rear drums or discs.

Technician A says a grinding, metal-on-metal noise during braking indicates friction material worn past its limit. Technician B says continued driving in that condition can score the rotor or drum. Who is correct?

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

When friction material wears away, the metal backing contacts the rotor or drum, producing a grinding noise, and continued driving scores the surface and raises repair cost. Both technicians are correct. Immediate pad or shoe replacement and surface inspection are required.

A rear disc parking brake that will not hold is often caused by:

• a.A misadjusted or seized parking brake mechanism/cable✓
• b.Air in the front lines
• c.Low battery voltage
• d.A failed wheel-speed sensor

Parking brake holding faults usually trace to cable stretch, misadjustment, or a seized caliper parking mechanism. Proper adjustment and lubrication restore holding force. On integral rear calipers, the internal actuator must function for both service and parking braking.

A brake caliper that sticks and does not release will most likely cause:

• a.A hard pedal at all times
• b.Dragging, overheating, and pulling to that side✓
• c.A soft pedal only
• d.Loss of all braking

A seized caliper keeps the pads applied, causing drag, excessive heat, uneven pad wear, and a pull toward that wheel. Overheated fluid can boil and reduce braking. Rebuilding or replacing the caliper and inspecting the slides and hose corrects it.

The metering valve in a combination valve is used to:

• a.Warn of ABS faults
• b.Bleed the master cylinder
• c.Increase rear brake pressure
• d.Delay front disc application so rear drums engage together✓

The metering valve holds off front disc pressure briefly so the rear drum shoes overcome their return springs and apply at nearly the same time, balancing braking. The proportioning section limits rear pressure to prevent lockup. Together these balance front-to-rear braking.

When bleeding a conventional hydraulic brake system, the general rule is to bleed:

• a.Only the front wheels
• b.All wheels at the same time
• c.In the sequence specified by the manufacturer, often longest line first✓
• d.Starting at the wheel nearest the master cylinder

Manufacturers specify a bleeding sequence, frequently starting at the wheel farthest from the master cylinder, to purge air effectively. Following the correct order and keeping the reservoir full prevents introducing more air. Some ABS units require a scan tool to bleed fully.

A proportioning valve in the brake system is designed to:

• a.Store extra brake fluid
• b.Reduce pressure to the rear brakes to prevent early lockup✓
• c.Increase pressure to the front only
• d.Operate the parking brake

Because weight shifts forward during braking, the proportioning valve limits rear brake pressure to keep the rear wheels from locking prematurely. This maintains stability during hard stops. Many vehicles now handle this function electronically through ABS/EBD.

Technician A says silicone (DOT 5) and glycol (DOT 3/4) brake fluids can be freely mixed. Technician B says brake fluid type is unimportant. Who is correct?

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

Silicone and glycol fluids are not compatible and must not be mixed, and using the wrong fluid type can damage seals and reduce performance. Both technicians are incorrect. Always use the fluid specification listed for the vehicle.

Using Ohm's law, a 12-volt circuit with 4 ohms of resistance will carry a current of:

• a.3 amps✓
• b.16 amps
• c.0.33 amps
• d.48 amps

Ohm's law states current equals voltage divided by resistance, so 12 volts divided by 4 ohms equals 3 amps. Understanding this relationship is essential for diagnosing circuit faults. Higher resistance in a circuit reduces current flow for a given voltage.

Technician A says a voltage-drop test across a battery cable can reveal unwanted resistance. Technician B says a voltage-drop test is more accurate than a visual inspection for finding poor connections. Who is correct?

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

A voltage-drop test measures the voltage lost across a connection under load, so high drop reveals corrosion or loose connections that a visual check may miss. Both technicians are correct. Acceptable drop is typically a few tenths of a volt or less.

A fully charged 12-volt lead-acid battery at rest should read approximately:

• a.13.8 volts
• b.11.8 volts
• c.10.5 volts
• d.12.6 volts✓

A healthy, fully charged 12-volt battery reads about 12.6 volts open-circuit at rest. Around 12.4 is roughly 75 percent, and 12.0 is about 25 percent charged. A surface charge should be removed before testing for accuracy.

Technician A says the charging system voltage at the battery with the engine running should typically be around 13.5 to 14.5 volts. Technician B says it should read exactly 12.6 volts while running. Who is correct?

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

With the engine running, the alternator should raise system voltage to roughly 13.5 to 14.5 volts to charge the battery and run loads. A reading of 12.6 running would indicate the charging system is not working. Technician B describes a resting, not charging, voltage.

Two 6-ohm resistors connected in parallel produce a total resistance of:

• a.6 ohms
• b.12 ohms
• c.0.5 ohms
• d.3 ohms✓

For two equal resistors in parallel, total resistance is half of one resistor, so two 6-ohm resistors equal 3 ohms. Parallel resistance is always lower than the smallest branch. This principle explains why adding parallel loads increases total current draw.

An open in a series circuit will cause:

• a.Higher voltage at the load
• b.Increased current flow
• c.No current flow in the circuit✓
• d.Reduced resistance

A series circuit has only one path, so an open anywhere stops all current and the load will not operate. Voltage will be present up to the open point when tested. Locating the open often uses a test light or voltmeter along the circuit.

A starter that cranks slowly, with the battery known good and fully charged, most likely has:

• a.A weak alternator
• b.A blown headlight fuse
• c.High resistance in the starter circuit or a failing starter✓
• d.Too little engine oil

Slow cranking with a good battery points to high resistance in the cables/connections or a worn starter, both of which limit current to the motor. A starter-circuit voltage drop test isolates the problem. Clean, tight connections are essential for full cranking current.

Power (watts) in an electrical circuit is calculated by:

• a.Voltage multiplied by current✓
• b.Voltage divided by resistance
• c.Resistance multiplied by voltage
• d.Current divided by voltage

Electrical power equals voltage times current (P = E x I). A 12-volt circuit drawing 5 amps consumes 60 watts. This relationship helps size fuses, wiring, and components for their load.

A parasitic (key-off) battery drain is measured by connecting an ammeter:

• a.In series between a battery terminal and the cable✓
• b.In parallel across the battery terminals
• c.Across a spark plug
• d.Between two ground points

Parasitic draw is measured by placing an ammeter in series in the battery circuit after modules go to sleep. Excessive draw discharges the battery overnight. Pulling fuses one at a time while watching the meter isolates the offending circuit.

In a wiring diagram, a component shown connected to ground provides:

• a.Signal amplification
• b.Fuse protection
• c.The return path for current back to the battery negative✓
• d.The source of voltage

Ground is the return path that completes the circuit back to the battery's negative terminal. A poor ground raises resistance and causes dim lights, erratic operation, or feedback. Diagrams use ground symbols to trace current return paths.

Technician A says a fuse that blows again immediately after replacement indicates a short to ground or an overload. Technician B says repeatedly replacing the fuse will fix the circuit. Who is correct?

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

A fuse that blows again immediately is protecting the circuit from a short to ground or an overload drawing excess current. Technician B is wrong because the underlying fault, not the fuse, must be repaired. Inspect the wiring for chafing and test the component.

Technician A says a diode allows current to flow in only one direction. Technician B says alternators use diodes to rectify AC into DC. Who is correct?

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

A diode conducts in one direction only, and the alternator's diode (rectifier) bridge converts the stator's AC into the DC the vehicle uses. Both statements are correct. A shorted or open diode causes low output and AC ripple on the charging system.

Excessive AC ripple voltage measured at the battery with the engine running usually indicates:

• a.One or more failed alternator diodes✓
• b.A stuck thermostat
• c.A weak starter
• d.A blown headlight bulb

Failed rectifier diodes let AC leak through, producing measurable ripple and reduced DC output. A meter set to AC volts or an oscilloscope reveals it. This often causes charging complaints and can disturb electronic modules.

Technician A says a relay lets a small control current switch a larger load. Technician B says relays protect switches and allow smaller control wiring. Who is correct?

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

A relay uses a low-current coil to close contacts that carry a high-current load, which protects switches and permits smaller control wiring. Both technicians are correct. Common uses include headlights, fuel pumps, and cooling fans.

Dim headlights that brighten when engine rpm increases most likely indicate:

• a.A shorted headlight switch
• b.A blown fuse
• c.An open ground on one lamp
• d.A weak battery or undercharging condition✓

Lights that brighten with rpm suggest the charging system is barely keeping up, so a weak battery or low alternator output is likely. A charging system test measures output under load. A high-resistance connection can also dim lights but usually affects specific circuits.

A voltmeter is connected how, relative to the component being tested?

• a.After removing the fuse
• b.Between the two battery posts only
• c.In series with the load
• d.In parallel (across) the component✓

A voltmeter is connected in parallel across the component or connection to measure the voltage difference, since it has very high internal resistance. An ammeter, by contrast, connects in series. Connecting a voltmeter in series would give an incorrect reading.

The gauge or module that displays engine coolant temperature relies on a sensor whose resistance:

• a.Changes with temperature (a thermistor)✓
• b.Produces AC voltage
• c.Stays constant regardless of temperature
• d.Only works above 200 degrees

Most coolant temperature sensors are thermistors whose resistance falls as temperature rises (negative temperature coefficient). The computer or gauge interprets this changing resistance as temperature. A faulty sensor can cause inaccurate readings and driveability or fan-control problems.

A circuit has 12 volts applied and draws 2 amps. Its total resistance is:

• a.6 ohms✓
• b.2 ohms
• c.24 ohms
• d.0.17 ohms

By Ohm's law, resistance equals voltage divided by current, so 12 volts divided by 2 amps equals 6 ohms. Rearranging Ohm's law lets a technician solve for any unknown value. Verifying calculated resistance against measured values helps confirm circuit condition.

In an automotive A/C system, the compressor's job is to:

• a.Store refrigerant
• b.Absorb moisture from the refrigerant
• c.Raise refrigerant pressure and circulate it through the system✓
• d.Condense refrigerant into a liquid

The compressor pressurizes low-pressure refrigerant vapor and pumps it through the system, raising its temperature and pressure before the condenser. It is the pump that drives the refrigeration cycle. A failed compressor clutch or internal damage stops cooling.

The component that changes high-pressure refrigerant vapor into a liquid by removing heat is the:

• a.Expansion valve
• b.Accumulator
• c.Condenser✓
• d.Evaporator

The condenser, mounted in front of the radiator, rejects heat so the high-pressure vapor condenses into a liquid. Airflow across it is essential; a blocked or dirty condenser causes high pressures and poor cooling. The evaporator, by contrast, absorbs heat inside the vehicle.

The evaporator in the passenger compartment:

• a.Rejects heat to the outside air
• b.Stores excess refrigerant
• c.Absorbs heat from cabin air, cooling it✓
• d.Compresses the refrigerant

As low-pressure liquid refrigerant boils in the evaporator, it absorbs heat from the cabin air blown across it, cooling and dehumidifying the air. A restricted or iced evaporator reduces airflow and cooling. Proper refrigerant charge and airflow keep it working correctly.

Technician A says overcharging an A/C system improves cooling. Technician B says overcharging raises system pressures and can reduce cooling and damage the compressor. Who is correct?

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

Overcharging raises high-side pressure, reduces cooling efficiency, and can damage the compressor with liquid slugging. The correct charge, measured by weight, is critical. Technician A is wrong; more refrigerant is not better.

The expansion valve or orifice tube controls:

• a.The flow of refrigerant into the evaporator, causing a pressure drop✓
• b.Compressor speed
• c.Blower motor voltage
• d.Cabin air recirculation

The metering device drops the refrigerant pressure and controls flow into the evaporator, allowing it to boil and absorb heat. A restricted orifice or stuck valve causes poor cooling and abnormal pressures. It separates the high side from the low side of the system.

The desiccant in a receiver-drier or accumulator is used to:

• a.Add oil to the system
• b.Absorb moisture from the refrigerant✓
• c.Increase refrigerant pressure
• d.Cool the condenser

The desiccant removes moisture that would otherwise form acids and ice, protecting the system. It should be replaced whenever the system is opened for major service. Saturated desiccant can break down and contaminate the system.

Technician A says a low refrigerant charge typically shows low readings on both gauges with poor cooling. Technician B says the leak should be repaired before recharging to the correct weight. Who is correct?

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

An undercharge shows low readings on both gauges with weak cooling and rapid cycling, and any leak must be repaired before recharging by weight. Both technicians are correct. Dye or an electronic detector locates the leak source.

Technician A says cabin heat comes from engine coolant flowing through the heater core. Technician B says a leaking heater core can fog the windshield and leave a sweet smell. Who is correct?

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

The heater core transfers heat from hot engine coolant to cabin air, and a leaking core lets coolant fog the glass and produce a sweet odor. Both technicians are correct. A clogged core or low coolant reduces heat output.

Technician A says a stuck-closed blend-air door can cause no heat even with a good heater core. Technician B says a failed blower motor can cause no airflow from the vents. Who is correct?

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

A blend door controls how much air passes over the heater core, so a stuck door can cause no heat, and a failed blower stops airflow entirely. Both technicians are correct. Actuator and door faults are common causes of temperature-control complaints.

Before servicing an A/C system, refrigerant must be:

• a.Mixed with fresh oil
• b.Vented outdoors quickly
• c.Recovered with approved equipment, not vented to the atmosphere✓
• d.Frozen in the condenser

Regulations require recovering refrigerant with certified equipment rather than releasing it, because it is a controlled substance. Recovery, recycling, and recharging equipment protects the environment and allows accurate recharging. Technicians handling refrigerant must be certified.

An A/C compressor clutch that will not engage could be caused by all of the following EXCEPT:

• a.A low-refrigerant lockout from the pressure switch
• b.A clogged cabin air filter✓
• c.A blown clutch fuse or relay
• d.An open clutch coil

The clutch may fail to engage due to a low-charge lockout, electrical faults, or an open coil, but a dirty cabin filter only reduces airflow, not clutch engagement. Diagnosis checks power, ground, and the pressure switches. A cabin filter affects volume, not the refrigerant cycle.

Higher-than-normal readings on both the high and low sides of an A/C system, with poor cooling, could indicate:

• a.A stuck-open thermostat
• b.An overcharge or a condenser airflow/cooling problem✓
• c.An open blower resistor
• d.A low refrigerant charge

High readings on both gauges often point to an overcharge or inadequate condenser cooling from a blocked condenser or inoperative cooling fan. Verifying charge weight and fan operation is the next step. Correcting airflow and charge restores normal pressures.

An oxygen (O2) sensor in the exhaust provides feedback to the PCM about:

• a.Ignition timing advance
• b.Engine oil level
• c.The air-fuel ratio (rich or lean)✓
• d.Coolant temperature

The oxygen sensor measures residual oxygen in the exhaust, telling the PCM whether the mixture is rich or lean so it can adjust fuel trim. A lazy or failed sensor degrades fuel control and emissions. Wide-band sensors report the actual ratio rather than just rich/lean.

A diagnostic trouble code (DTC) of P0301 indicates:

• a.A lean condition on bank 1
• b.An EVAP leak
• c.A faulty coolant sensor
• d.A misfire detected in cylinder number 1✓

P0301 is a cylinder-specific misfire code, with the last digit identifying cylinder 1. P0300 indicates a random/multiple-cylinder misfire. Causes include ignition, fuel, or mechanical (compression) problems in that cylinder.

Technician A says a vacuum leak causes a rich condition. Technician B says a vacuum leak adds unmetered air and causes a lean condition, especially at idle. Who is correct?

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

A vacuum leak lets extra air enter after the mass airflow sensor, leaning the mixture and often causing a rough idle and positive fuel trim. Technician B is correct. Smoke testing helps locate intake leaks.

Technician A says a positive long-term fuel trim of +20 percent means the PCM is adding fuel to correct a lean condition. Technician B says positive trim means the engine is running rich. Who is correct?

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

Positive fuel trim means the computer is adding fuel to correct a lean condition from a vacuum leak, low fuel pressure, or a dirty MAF. Technician B is wrong because rich conditions produce negative trims. Comparing short- and long-term trims helps pinpoint the fault.

Technician A says a rich air-fuel mixture can raise tailpipe CO and HC. Technician B says the oxygen sensor helps the PCM keep the mixture near stoichiometric. Who is correct?

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

A rich mixture leaves excess fuel that raises carbon monoxide and hydrocarbons, and the oxygen sensor feedback lets the PCM hold the mixture near the ideal ratio. Both technicians are correct. A lazy sensor degrades fuel control and emissions.

Technician A says the MAF sensor measures the mass of air entering the engine so the PCM can meter fuel. Technician B says a dirty MAF can cause hesitation and fuel-trim errors. Who is correct?

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

The MAF sensor measures intake air mass so the PCM meters the correct fuel quantity, and a dirty or faulty MAF causes incorrect fueling, hesitation, and trim errors. Both technicians are correct. Diagnosis includes cleaning or replacing it and checking for unmetered air leaks.

A P0420 code (catalyst efficiency below threshold) most often indicates:

• a.A slipping transmission
• b.A faulty ABS sensor
• c.A degraded catalytic converter or an O2 sensor issue✓
• d.A worn wheel bearing

P0420 sets when the downstream O2 sensor signal mirrors the upstream too closely, suggesting the converter is no longer storing oxygen effectively. Causes include a worn converter, exhaust leaks, or faulty sensors. Underlying misfires or rich running can damage the converter and must be addressed first.

In a modern coil-on-plug ignition system, each coil:

• a.Stores fuel for injection
• b.Is triggered by a mechanical distributor
• c.Fires the spark plug directly on its cylinder, controlled by the PCM✓
• d.Powers all cylinders at once

Coil-on-plug systems place an individual coil at each spark plug, fired by the PCM through the ignition driver, eliminating plug wires and the distributor. This improves spark control and misfire diagnosis. A failed coil typically causes a cylinder-specific misfire code.