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ASE G1 practice questions

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Question 1Engine Systems

An engine's coolant temperature gauge reads lower than normal after 20 minutes of highway driving, and the heater blows only warm air. Which condition best explains these symptoms?

  1. A radiator cap with a weak pressure spring
  2. A restricted heater core
  3. A coolant level that is too low
  4. A thermostat stuck open Correct answer.

Explanation

A thermostat that stays open lets coolant circulate through the radiator continuously, so the engine never reaches normal operating temperature and heater output stays weak. Coolant temperature that is too low after extended driving is the classic signature of this failure.

Question 2Engine Systems

In a multigrade oil labeled 5W-30, what does the 5W designate?

  1. The oil's viscosity grade at operating temperature
  2. The oil's recommended drain interval
  3. The oil's low-temperature flow rating Correct answer.
  4. The oil's API service classification

Explanation

The W in a multigrade oil stands for winter, and the number preceding it rates how the oil flows when cold. The number after the W describes viscosity at operating temperature, which in this case is the 30 grade.

Question 3Engine Systems

A restricted engine air filter most directly causes which condition?

  1. An excessively lean mixture at idle speed
  2. Over-advanced ignition timing under load
  3. Reduced airflow at high engine speed Correct answer.
  4. Higher-than-normal engine oil pressure at idle

Explanation

The air filter's job is to supply the engine with unrestricted air, so a clogged element limits airflow most noticeably when demand is highest, such as at high engine speed. The result is reduced power and sometimes a richer mixture under load.

Question 4Engine Systems

A spark plug removed from one cylinder is black and wet with oil. Which condition is the most likely cause?

  1. An ignition timing advance that is too great
  2. A spark plug heat range that is too hot
  3. Worn valve guides or piston rings Correct answer.
  4. An intake manifold vacuum leak at that runner

Explanation

Wet, oily deposits mean oil is entering the combustion chamber and not burning cleanly. Worn valve guides or worn rings are the usual sources of that oil, and further testing such as a wet compression test can separate them.

Question 5Engine Systems

A high-pitched squeal from the accessory drive that is loudest right after a cold start and then fades most likely indicates:

  1. A glazed or slipping drive belt Correct answer.
  2. A restricted PCV valve
  3. A worn timing chain tensioner
  4. A faulty coolant temperature sensor

Explanation

A belt whose friction surface is glazed or that is improperly tensioned slips under the load of the alternator and other accessories, producing a squeal that is worst on a cold start. Proper belt tension and pulley alignment are the first checks.

Question 6Engine Systems

What is the primary purpose of the positive crankcase ventilation (PCV) system?

  1. To relieve excess pressure from the cooling system
  2. To recirculate a portion of exhaust gas into the intake
  3. To add oil mist to the intake charge for upper-cylinder lubrication
  4. To route crankcase vapors into the intake to be burned Correct answer.

Explanation

Blowby gases that collect in the crankcase contain unburned hydrocarbons, and the PCV system meters them back into the intake so they are consumed in combustion. This also prevents pressure from building and pushing oil past seals.

Question 7Engine Systems

During a compression test, holding the throttle wide open while cranking mainly serves to:

  1. Prevent the ignition coil from firing
  2. Allow maximum air into the cylinder Correct answer.
  3. Raise engine oil pressure during cranking
  4. Keep the fuel injectors from firing

Explanation

Compression readings depend on how much air is trapped in the cylinder, so the throttle plate must be open to admit a full charge. Restricting the intake would lower every reading and give a false impression of mechanical wear.

Question 8Engine Systems

Why is a 50/50 mix of antifreeze and water normally used instead of pure antifreeze?

  1. Pure antifreeze transfers heat out of the engine better than water does
  2. Water carries heat better; antifreeze adds freeze and corrosion protection Correct answer.
  3. Water alone provides all the corrosion protection an aluminum engine needs
  4. Pure antifreeze has a lower freezing point than any water and antifreeze blend

Explanation

Water is a superior heat-transfer fluid, but it freezes at a high temperature and promotes corrosion. Ethylene glycol lowers the freezing point and contains inhibitors, and the 50/50 blend balances heat transfer with protection.

Question 9Engine Systems

While a cylinder leak-down test is being performed, air bubbles continuously rise in the radiator. What does this indicate?

  1. A leaking intake valve in that cylinder
  2. A leaking head gasket or a crack into the water jacket Correct answer.
  3. Worn piston rings in the cylinder being tested
  4. A restricted radiator core

Explanation

The leak-down tester pressurizes the cylinder with the valves closed, so escaping air is traced by where it appears. Bubbles in the cooling system mean the pressurized air has found a path into a water jacket, which points to the head gasket or a cracked casting.

Question 10Engine Systems

An engine overheats while idling in traffic with the A/C on but stays normal at highway speed, and the electric cooling fan never runs. Which is the most likely cause?

  1. A leaking heater core
  2. An open circuit or failed fan motor Correct answer.
  3. A radiator cap with a weak spring
  4. A thermostat stuck in the open position

Explanation

At highway speed ram air moves enough air through the radiator, but at a standstill the electric fan must do that job. Overheating only when stopped, combined with a fan that never runs, points to the fan circuit or motor.

Question 11Engine Systems

An oil pressure warning light flickers at a hot idle and goes out above 1500 rpm; the oil level is correct. What is the most likely cause?

  1. An oil viscosity that is too high
  2. A restricted engine air filter element
  3. A stuck-open engine thermostat
  4. Worn bearings or a weak oil pump Correct answer.

Explanation

Oil pressure falls as clearances open up and as pump output drops, and low pressure first becomes visible at idle when pump speed is lowest. Pressure that recovers as rpm rises is typical of excessive bearing clearance or a worn pump.

Question 12Engine Systems

Fuel pressure is within specification at idle but drops below specification under heavy load, and the vehicle loses power. Which is the most likely cause?

  1. A restricted fuel filter Correct answer.
  2. A clogged air filter element
  3. A failing ignition coil
  4. A leaking intake manifold gasket

Explanation

When fuel demand rises under load, a restricted filter or a weak pump cannot keep volume up, so pressure falls and the engine runs lean and loses power. Pressure that is normal at idle but drops under demand is the key clue.

Question 13Engine Systems

A P0302 misfire code follows cylinder 2. After the coil from cylinder 2 is moved to cylinder 4, the misfire moves to cylinder 4. What is indicated?

  1. A leaking fuel injector in cylinder 2
  2. A mechanical fault in cylinder 2
  3. A faulty ignition coil Correct answer.
  4. A faulty spark plug in cylinder 2

Explanation

The misfire followed the part that was moved, which is the definition of a part-specific failure. Because the coil was the component swapped, the coil is the cause.

Question 14Engine Systems

A spark plug with a heat range that is too hot for the application can cause:

  1. A lower-than-normal tip temperature
  2. Heavy carbon fouling of the spark plug insulator
  3. Pre-ignition and electrode burning Correct answer.
  4. Oil fouling of the electrodes

Explanation

A hot plug conducts less heat away from the tip, so it runs above its designed temperature and can glow hot enough to ignite the mixture before the spark occurs. The result is pre-ignition, blistered insulators and burned electrodes.

Question 15Engine Systems

A vacuum gauge on the intake manifold reads normal at idle but drops steadily while the engine is held at 2500 rpm. Which condition is most likely?

  1. A cracked spark plug insulator
  2. A worn timing chain
  3. A restricted exhaust system Correct answer.
  4. A lean fuel mixture

Explanation

As exhaust flow increases with engine speed, a restricted converter or crushed pipe causes backpressure to build and manifold vacuum to fall. A vacuum reading that is normal at idle and declines with speed is a classic indicator of exhaust restriction.

Question 16Engine Systems

A ticking noise from the top of the engine that is loudest at startup and quiets once oil pressure builds most likely indicates:

  1. An exhaust manifold gasket leak
  2. A collapsed lifter Correct answer.
  3. A worn connecting rod bearing
  4. A loose spark plug

Explanation

Hydraulic lifters rely on oil pressure to maintain zero lash, so one that bleeds down overnight ticks until it refills. Noise that disappears as pressure builds is the characteristic pattern of a weak or collapsed lifter.

Question 17Engine Systems

After a coolant drain and refill, the engine overheats and the heater stays cold. Which is the most likely cause?

  1. A thermostat that opens too early
  2. Air trapped in the cooling system Correct answer.
  3. An antifreeze concentration that is too high
  4. A radiator cap rated too low

Explanation

Air pockets block coolant circulation, so the water pump cannot move liquid through the heater core or past the temperature sensor, and the engine overheats while the heater blows cold. The system must be bled at the specified points after a refill.

Question 18Engine Systems

On an interference engine, a timing belt that breaks while the engine is running will most likely cause:

  1. Valve-to-piston contact and major damage Correct answer.
  2. A coolant leak at the water pump
  3. An engine stall with no internal damage
  4. A blown head gasket only

Explanation

In an interference design the valves and pistons occupy the same space at different points in the cycle, and only the belt keeps them synchronized. Losing the belt lets pistons strike open valves, bending stems and often damaging guides and piston crowns.

Question 19Engine Systems

A vacuum gauge connected to the intake manifold reads a steady 10 in-Hg at idle, where specification is 18 to 22 in-Hg. Which is the most likely cause?

  1. A vacuum leak or retarded valve timing Correct answer.
  2. A glazed drive belt
  3. A weak battery
  4. A restricted exhaust system

Explanation

Manifold vacuum depends on the throttle restriction and on how efficiently the cylinders pump air. A leak admits unmetered air and late valve timing reduces pumping, so either condition produces a steady low reading.

Question 20Engine Systems

What is the purpose of the pressure rating marked on a radiator cap?

  1. It sets the maximum coolant temperature
  2. It controls when the thermostat opens
  3. It raises the coolant boiling point Correct answer.
  4. It limits coolant flow through the heater core

Explanation

Coolant boils at a higher temperature when the system is held under pressure, so the cap's spring rating determines the pressure the system maintains. A higher-rated cap raises the boiling point, allowing the engine to run hotter without boiling over.

Question 21Engine Systems

The fluid in a combustion gas (block) tester turns from blue to yellow while the engine is running. What does this indicate?

  1. The thermostat is stuck open
  2. Combustion gases are entering the cooling system Correct answer.
  3. The coolant is diluted with too much water
  4. The cooling system has an external leak

Explanation

The test fluid changes color when it contacts carbon dioxide, which is present in combustion gas but not normally in the cooling system. A color change confirms that cylinder pressure is escaping past the head gasket or through a crack into a water jacket.

Question 22Engine Systems

A cylinder produces 120 psi on a dry compression test and 165 psi after oil is added. What does this indicate?

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

Explanation

Oil temporarily seals the gap between rings and cylinder walls, so a large jump in the wet reading shows that pressure was escaping past the rings. Valve or gasket leaks do not seal appreciably when oil is added.

Question 23Engine Systems

During a cylinder balance test, disabling the injector for cylinder 3 causes no measurable drop in engine speed. What does this indicate?

  1. The overall fuel mixture is too lean
  2. Cylinder 3 is producing too much power
  3. The ignition timing is retarded
  4. Cylinder 3 is not producing power Correct answer.

Explanation

Each working cylinder contributes a share of engine power, so cutting its fuel should cause a noticeable rpm drop. When there is no change, that cylinder was already contributing nothing because of a spark, fuel or mechanical fault.

Question 24Engine Systems

Long-term fuel trim is +28% on both banks at idle and returns to near 0% at 2500 rpm. Which is the most likely cause?

  1. Low fuel pump pressure
  2. A vacuum leak in the intake Correct answer.
  3. Leaking fuel injectors
  4. A restricted exhaust system

Explanation

Unmetered air entering the intake has its greatest effect at idle, when the metered air charge is small, so the PCM adds fuel to compensate. When the leak becomes a smaller fraction of total airflow at higher rpm, the correction returns toward normal.

Question 25Engine Systems

A vehicle sets a P0016 camshaft/crankshaft correlation code and runs poorly. Which is the most likely cause?

  1. A weak ignition coil
  2. A clogged fuel filter
  3. A slow-responding oxygen sensor
  4. A stretched timing chain Correct answer.

Explanation

The code is set when the camshaft position no longer agrees with the crankshaft position within the expected window. Wear or stretch in the timing chain, or a jumped tooth, shifts cam timing and is the most common mechanical cause.

Question 26Automatic Transmission and Transaxle

Which statement describes the primary job of the torque converter?

  1. It locks the engine to the driveline whenever the throttle closes
  2. It changes the gear ratio at each shift point
  3. It multiplies torque at low speed and lets the engine idle in gear Correct answer.
  4. It provides engine braking in every forward gear

Explanation

The converter is a fluid coupling: the impeller throws oil into the turbine to move the car, and the stator redirects the returning oil so torque is multiplied at low speed. Because the coupling is fluid, the engine can idle while the car is held stationary in gear. Gear ratio changes are made by the planetary gearsets, not the converter.

Question 27Automatic Transmission and Transaxle

When is automatic transmission fluid level normally checked on a vehicle with a dipstick?

  1. Engine off, fluid cold, vehicle on a lift
  2. Engine idling in park, fluid hot, vehicle level Correct answer.
  3. Engine idling in drive, wheels blocked, fluid cold
  4. Engine off, fluid hot, after a 20-minute soak

Explanation

Most dipstick-equipped units are checked with the engine running so the pump keeps the converter and cooler full, with fluid at operating temperature and the car on a level surface. Checking with the engine off or cold gives a false reading because fluid drains back from the converter and cooler.

Question 28Automatic Transmission and Transaxle

What keeps the vehicle from rolling when Park is selected?

  1. A sprag holding the planetary carrier
  2. Line pressure applied to the forward clutch
  3. A band tightened around the output drum
  4. A pawl engaged in a toothed gear on the output shaft Correct answer.

Explanation

Park engages a spring-loaded parking pawl into notches on a park gear that is splined to the transmission output shaft, mechanically locking the driveline. The pawl is released by the manual valve linkage when the shifter leaves Park. No hydraulic apply device is used to hold the car in Park.

Question 29Automatic Transmission and Transaxle

Why does the torque converter clutch engage at steady cruise?

  1. To remove converter slip and improve fuel economy Correct answer.
  2. To cushion the driveline on wide-open-throttle shifts
  3. To let the engine idle without dragging the car
  4. To multiply engine torque during acceleration

Explanation

Above a calibrated speed and load, the converter clutch locks the turbine to the impeller so there is no slip, cutting heat and fuel use. Torque multiplication is the stator's job during acceleration, not something the clutch provides.

Question 30Automatic Transmission and Transaxle

How does a belt-drive CVT change its drive ratio?

  1. It engages different planetary gearsets
  2. It varies the working diameter of the two pulleys Correct answer.
  3. It slips a wet clutch to a controlled degree
  4. It switches between two fixed final-drive ratios

Explanation

In a belt or chain CVT, hydraulic pressure moves the halves of each pulley together or apart, changing the radius the belt rides on and therefore the ratio. Ratio change is stepless and continuous rather than a series of fixed steps.

Question 31Automatic Transmission and Transaxle

Which of these is an overdrive ratio?

  1. 1.00:1
  2. 3.20:1
  3. 0.70:1 Correct answer.
  4. 2.50:1

Explanation

An overdrive ratio is numerically less than 1.00:1, meaning the output shaft turns faster than the input. Ratios greater than 1.00:1 are reductions, and 1.00:1 is direct drive.

Question 32Automatic Transmission and Transaxle

What is the job of the manual valve?

  1. It routes line pressure to the circuits chosen by the shift lever Correct answer.
  2. It controls how fast a clutch applies during a shift
  3. It regulates line pressure according to engine load
  4. It locks the converter clutch at highway speed

Explanation

The manual valve is a spool moved by the shift lever through the cable or linkage. It does not regulate pressure; it simply sends line pressure to the circuits for the range the driver selected.

Question 33Automatic Transmission and Transaxle

Why is transmission fluid circulated through a cooler?

  1. To raise pressure before the fluid reaches the valve body
  2. To carry away heat made by the converter and clutches Correct answer.
  3. To separate air from the fluid before it returns to the pan
  4. To thicken the fluid so clutches hold better

Explanation

The converter and slipping clutches generate a lot of heat, and fluid temperature must be kept in a safe range to protect friction material and seals. The cooler, often inside the radiator plus an auxiliary unit, transfers that heat out.

Question 34Automatic Transmission and Transaxle

Stall speed is above specification in both Drive and Reverse. What does this most likely mean?

  1. The stator one-way clutch is slipping
  2. The converter clutch is stuck on
  3. Line pressure is low or an apply device is slipping Correct answer.
  4. The engine is down on power

Explanation

A stall test loads the engine against a held output. High stall speed in all ranges means the transmission cannot hold the engine, typically from low line pressure or slipping apply devices common to all ranges. Low stall speed, by contrast, points to an engine or stator problem.

Question 35Automatic Transmission and Transaxle

Line pressure reads low at idle in every range. Which is the most likely cause?

  1. A faulty pressure regulator valve or EPC solenoid Correct answer.
  2. A worn stator one-way clutch in the torque converter
  3. A leaking forward clutch piston seal inside the drum
  4. A misadjusted shift cable at the manual valve

Explanation

Line pressure is set by the pressure regulator and trimmed by the electronic pressure control solenoid. If pressure is low in every range, the fault is in a component that affects all circuits, such as the regulator, the EPC solenoid, or the pump. Range-specific leaks or linkage problems would not lower pressure everywhere.

Question 36Automatic Transmission and Transaxle

During an upshift, engine rpm rises briefly before the next gear takes hold. What is this condition and what does it mean?

  1. Flare, caused by a slipping or slow apply device Correct answer.
  2. Hunting, caused by a faulty shift solenoid
  3. Harsh engagement, caused by excessive line pressure
  4. Shudder, caused by converter clutch chatter at lockup

Explanation

Flare is a momentary loss of drive during a shift, seen as engine rpm climbing before the next ratio engages. It means the oncoming apply device is not holding full torque in time, from worn friction, a leaking seal, or low apply pressure.

Question 37Automatic Transmission and Transaxle

What does an accumulator do in a hydraulic valve body?

  1. It multiplies line pressure on wide-open-throttle shifts
  2. It vents excess pressure to the pan when fluid is cold
  3. It keeps the converter filled when the engine is off
  4. It cushions clutch apply to soften the shift Correct answer.

Explanation

An accumulator is a spring-loaded piston that absorbs part of the apply oil as a clutch fills, slowing the pressure rise and softening the shift. Once the piston bottoms, full apply pressure reaches the clutch.

Question 38Automatic Transmission and Transaxle

A simple planetary set has a 30-tooth sun gear and a 60-tooth ring gear. The ring gear is held, the sun gear is driven, and the carrier is the output. What is the ratio?

  1. 2.00:1
  2. 4.00:1
  3. 3.00:1 Correct answer.
  4. 1.50:1

Explanation

With the ring held and the sun driven, reduction equals 1 + (ring teeth / sun teeth). Here that is 1 + 60/30 = 3.00:1, so the carrier turns one revolution for every three input revolutions.

Question 39Automatic Transmission and Transaxle

A vehicle shudders as the converter clutch engages during light-throttle cruise. What is the most likely cause?

  1. A leaking output shaft seal
  2. A worn stator one-way clutch
  3. A slipping forward band
  4. Degraded fluid or a contaminated clutch facing Correct answer.

Explanation

Shudder during lockup comes from the clutch grabbing and releasing instead of applying smoothly. Degraded fluid, friction modifier depletion, or a contaminated converter clutch facing are the usual causes.

Question 40Automatic Transmission and Transaxle

Which solenoid sends fluid to the shift valves to change gears?

  1. The shift solenoid Correct answer.
  2. The line pressure switch
  3. The converter clutch solenoid
  4. The electronic pressure control solenoid

Explanation

Shift solenoids are turned on and off by the control module to direct or release fluid at the shift valves, which then apply and release the clutches and bands. The converter clutch solenoid and the EPC solenoid control different circuits.

Question 41Automatic Transmission and Transaxle

The owner's manual calls for a specific ATF, but the shop only stocks a universal fluid. What should be done?

  1. Use engine oil of the same viscosity until the correct fluid arrives
  2. Mix two different ATFs to approximate the required specification
  3. Use the universal fluid, since all ATFs are interchangeable
  4. Use a fluid meeting the manufacturer's specification Correct answer.

Explanation

Friction characteristics and seal compatibility are engineered for each unit, so the fluid must meet the published specification. A fluid that carries the correct approval is acceptable even if it is sold as a multi-vehicle product; an unapproved fluid is not.

Question 42Automatic Transmission and Transaxle

What is the usual procedure for adjusting an automatic transmission band?

  1. Adjust until the band drags heavily on the drum
  2. Tighten to the specified torque, then back off the specified turns Correct answer.
  3. Tighten the screw fully and lock it with the jam nut
  4. Back the screw out fully and let line pressure seat the band

Explanation

Band adjustment sets a specific clearance between band lining and drum. The adjusting screw is torqued to seat the band, then backed off a stated number of turns to establish that clearance before the locknut is tightened.

Question 43Automatic Transmission and Transaxle

ATF is leaking at the left front wheel area of a front-drive transaxle. What is the most likely source?

  1. A leaking transmission pan gasket
  2. A worn differential axle output shaft seal Correct answer.
  3. A failed torque converter hub seal
  4. A cracked transmission cooler line

Explanation

On a transaxle, the halfshaft passes through a seal at the differential output; a worn seal or a damaged joint boot area lets ATF escape at the wheel. Converter and pan leaks show up at the bellhousing and pan, not out at the wheel.

Question 44Automatic Transmission and Transaxle

A car's engine will start with the shifter in Drive as well as in Park and Neutral. What is the most likely cause?

  1. A bad brake pedal switch
  2. A shorted ignition switch
  3. A faulty starter motor
  4. A misadjusted or faulty transmission range sensor Correct answer.

Explanation

The range sensor tells the control module which range is selected and enables cranking only in Park and Neutral. If it reports Park/Neutral while the lever is in Drive, the starter will crank in gear.

Question 45Automatic Transmission and Transaxle

What does the stator do in a torque converter?

  1. Locks the turbine to the impeller at cruise speed
  2. Absorbs engine torsional vibration at idle
  3. Drives the transmission oil pump through the hub
  4. Redirects turbine oil back to the pump to multiply torque Correct answer.

Explanation

The stator sits on a one-way clutch between the turbine and impeller. At low speed it stays stationary and redirects oil leaving the turbine so it assists impeller rotation, which multiplies torque; at coupling speed it freewheels.

Question 46Automatic Transmission and Transaxle

The fluid on the dipstick is dark and smells burnt. What does this indicate and what should be done?

  1. Normal fluid life; top off and return the car
  2. Correct fluid for a CVT; no action needed
  3. Too much fluid; drain to the full mark and release
  4. Overheated fluid; find the cause and repair as needed Correct answer.

Explanation

A burnt smell and dark color mean the fluid has been overheated, which usually comes from slipping apply devices, a restricted cooler, or heavy loading. The cause must be found, since new fluid alone will overheat again.

Question 47Automatic Transmission and Transaxle

A planetary set has a 24-tooth sun gear and a 72-tooth ring gear. The sun is held, the ring is driven, and the carrier is the output. What is the ratio?

  1. 0.75:1 Correct answer.
  2. 1.33:1
  3. 4.00:1
  4. 3.00:1

Explanation

With the sun held and the ring driven, the ratio is ring teeth divided by the sum of ring and sun teeth: 72 / (72 + 24) = 0.75:1. A result below 1.00:1 is overdrive, so the carrier turns faster than the ring.

Question 48Automatic Transmission and Transaxle

A transaxle moves normally in Reverse but will not move in any forward range. What is the most likely cause?

  1. A faulty converter clutch solenoid
  2. A failed forward clutch or forward one-way clutch Correct answer.
  3. A worn stator one-way clutch
  4. A failed low/reverse band

Explanation

A component common to all forward ranges but not used in Reverse is the likely fault, and the forward clutch and its one-way clutch fit that description. Reverse still works because it uses the low/reverse band and a different torque path.

Question 49Automatic Transmission and Transaxle

What does raising throttle valve (modulator) pressure accomplish?

  1. Raises line pressure and delays upshifts under load Correct answer.
  2. Applies the converter clutch sooner at cruise
  3. Lowers line pressure to soften light-throttle shifts
  4. Lowers governor pressure to advance the shift points

Explanation

Throttle pressure rises with engine load and acts on the pressure regulator and shift valves. Higher throttle pressure raises line pressure for greater holding force and raises the speed at which upshifts occur.

Question 50Automatic Transmission and Transaxle

An engine stalls as the car comes to a stop in Drive, then restarts and drives fine. What is the most likely cause?

  1. A low/reverse band that is dragging badly
  2. A worn transmission oil pump
  3. The transmission has entered limp-home mode
  4. A converter clutch that stays applied Correct answer.

Explanation

If the converter clutch does not release as the vehicle slows, the engine is mechanically tied to the driveline and is dragged to a stall at a stop. Releasing the brake or shifting to neutral restores idle, which matches the complaint.