ASE Practice Test (A2: Automatic Transmission/Transaxle) 2 — Questions and Answers

Question 1: A customer complains that their automatic transmission slips only when cold and shifts normally once at operating temperature. What is the MOST likely cause?

Worn clutch packs throughout the transmission
Low transmission fluid level
Worn or swollen sealing rings on a clutch drum (Correct answer)
Faulty transmission range sensor

Correct answer: Worn or swollen sealing rings on a clutch drum

Sealing rings on clutch drums can shrink when cold, allowing hydraulic pressure to leak past them. As the transmission warms up, the rings expand and seal properly, eliminating the slip. This is a classic symptom of worn or hardened sealing rings.

Automatic transmissions use hydraulic pressure to apply clutch packs and bands that determine which gear is engaged. Sealing rings, typically made of cast iron, Teflon, or nylon, are used on rotating clutch drum hubs to maintain hydraulic pressure in the apply circuits. When sealing rings wear, they lose their ability to maintain a proper seal. This is especially problematic when cold because metal contracts in cold temperatures, widening any gaps. Additionally, transmission fluid is thicker (higher viscosity) when cold, but if sealing rings are worn enough, cold fluid cannot build sufficient pressure quickly enough to fully apply the clutch pack. As the transmission reaches operating temperature, the sealing rings expand with heat, improving their sealing ability. At the same time, fluid thins out and flows more freely, allowing the apply circuits to pressurize more quickly. Together, these factors restore normal clutch application and eliminate the slip. Other cold-specific issues include stuck check balls in the valve body or cold-hardened accumulator seals, but sealing rings are the most common cause of cold-only slip. Low fluid would cause slipping in all temperatures. Worn clutch packs would worsen with heat, not improve. A range sensor fault would typically cause incorrect gear selection or engagement issues, not slip.

Question 2: During a line pressure test on an automatic transmission, the technician finds pressure is within specifications in all ranges except Reverse, where it is very low. What area should be inspected first?

The main pressure regulator valve
The reverse clutch pack and its apply circuit (Correct answer)
The torque converter clutch solenoid
The transmission oil pump

Correct answer: The reverse clutch pack and its apply circuit

When line pressure is correct in all forward ranges but low only in Reverse, the problem is isolated to the reverse-specific hydraulic circuit. The reverse clutch pack, its seals, or the hydraulic passages feeding it are the primary suspect.

Transmission line pressure testing involves connecting a pressure gauge to test ports in the transmission case and measuring hydraulic pressure at specified RPM and load conditions. This test differentiates between problems in the transmission's hydraulic pump/regulator circuit versus problems in specific gear-apply circuits. Normal line pressure in all forward ranges confirms the main pump, pressure regulator valve, and main hydraulic circuit are functioning properly. Low pressure only in Reverse means the pressure is being lost somewhere in the reverse-specific hydraulic path. The reverse gear hydraulic circuit includes the reverse clutch pack seals (piston seal and drum seals), the reverse clutch apply passage in the case, and the related valve body passages. A leak in any of these areas will drop pressure in Reverse without affecting forward gear circuits. Common causes include a torn reverse clutch piston seal, worn sealing rings on the reverse drum, or a damaged or missing checkball in the reverse apply passage of the valve body. A main pump or regulator problem would affect all ranges equally. The torque converter clutch solenoid controls lockup in higher gears and would not affect reverse line pressure.

Question 3: A technician is performing a stall test on a vehicle with an automatic transmission. The stall speed is 200 RPM HIGHER than the manufacturer's specification. What does this indicate?

The torque converter is faulty and the stator is freewheeling
The transmission has a slipping clutch pack or band (Correct answer)
The engine is producing too much power
The transmission fluid is overheating

Correct answer: The transmission has a slipping clutch pack or band

During a stall test, a higher-than-specified stall RPM indicates that the transmission is slipping internally. The engine can rev higher than normal because the transmission clutches or bands are not holding the load, preventing the torque converter from being properly loaded.

The stall test is performed by applying firm pressure to both the brake and accelerator pedals simultaneously with the transmission in Drive (or Reverse), holding wide-open throttle for no more than 5 seconds, and recording the maximum RPM reached. This tests the holding capacity of the transmission's applied clutch/band and the torque converter's stator function. Normal stall speed (typically 1,800-2,500 RPM depending on the vehicle) represents the RPM at which the torque converter impeller's hydraulic force is exactly balanced by the resistance of the stalled output. When the transmission clutches or bands slip, the output shaft is not truly held stationary — it creeps or slips. This reduces the hydraulic load on the torque converter, allowing the engine to rev higher than intended. A stall speed 200 RPM above specification in Drive points to a slipping forward clutch pack or forward band. In Reverse, a high stall would point to the reverse clutch or low-reverse band/clutch. Conversely, a stall speed LOWER than specification indicates a weak engine (insufficient power to overcome the converter load at spec RPM) or a faulty torque converter stator that is freewheeling rather than redirecting fluid. Always observe the 5-second maximum test time to prevent overheating the fluid and always allow the vehicle to idle in Neutral for one minute between tests.

Question 4: What is the function of the torque converter stator?

To directly connect the engine and transmission at highway speeds
To redirect fluid from the turbine back to the impeller to multiply torque (Correct answer)
To regulate hydraulic line pressure within the torque converter
To prevent the torque converter from spinning in the wrong direction

Correct answer: To redirect fluid from the turbine back to the impeller to multiply torque

The stator is positioned between the impeller and turbine inside the torque converter. It redirects transmission fluid exiting the turbine back in the same direction as the impeller rotation, allowing the converter to multiply engine torque during low-speed acceleration.

A torque converter consists of three main rotating elements: the impeller (pump), the turbine, and the stator. The impeller is attached to the engine, the turbine to the transmission input shaft, and the stator is mounted on a one-way clutch attached to the transmission case (it cannot rotate backward). At low speeds when there is a large speed difference between the impeller and turbine (high slip), fluid exiting the turbine is moving in a direction opposite to impeller rotation. Without the stator, this fluid would return to the impeller and partially oppose its rotation, reducing efficiency. The stator's curved vanes catch this returning fluid and redirect it so it re-enters the impeller in the same rotational direction. This adds to the force driving the impeller, effectively multiplying the torque being transmitted to the turbine. Torque multiplication ratios of 2:1 to 2.5:1 are common at stall. As vehicle speed increases and converter slip decreases, the fluid exiting the turbine changes direction. At the coupling point (approximately 85-90% of stall speed), the stator's one-way clutch begins to freewheel, as continuing to redirect fluid would cause efficiency losses. The converter then functions as a simple fluid coupling. The torque converter clutch (TCC) mechanically locks the impeller and turbine together for maximum efficiency at cruise speeds.

Question 5: An automatic transmission exhibits harsh engagement when shifting from Park to Drive or Reverse while cold. The condition improves when warm. What is the MOST likely cause?

Worn front pump seal
Contaminated transmission fluid causing sticky valve body valves
Accumulator piston issues affecting shift cushioning (Correct answer)
Faulty vehicle speed sensor

Correct answer: Accumulator piston issues affecting shift cushioning

Accumulators cushion gear engagement by providing a temporary fluid volume that absorbs initial apply pressure spikes. Worn or hardened accumulator piston seals are less effective when cold, allowing harsh initial engagement that smooths out as seals become more pliable at operating temperature.

Accumulators are hydraulic shock absorbers within the transmission's hydraulic control system. Each major clutch pack typically has an associated accumulator consisting of a piston and spring in a bore. When the clutch apply circuit is pressurized, some fluid initially fills the accumulator cavity, momentarily slowing the pressure rise to the clutch. This gradual pressure buildup results in a smooth, progressive clutch engagement rather than a sudden jolt. Accumulator pistons are sealed with O-rings or lip seals. When these seals wear or become hard (particularly in cold conditions), they may not properly seal the accumulator bore. If the accumulator cannot fill quickly enough due to seal leakage, the full apply pressure reaches the clutch pack without the cushioning effect, resulting in harsh engagement. This condition being worse when cold and improving with heat is explained by seal materials becoming more pliable as they warm up, better conforming to the accumulator bore and restoring some cushioning function. Additionally, cold fluid is thicker and flows more slowly into the accumulator, further affecting the timing of cushioning. Contaminated fluid can cause sticky valve body valves that result in delayed or erratic shifts, not specifically harsh cold engagement. A faulty vehicle speed sensor would cause shift point problems, not engagement harshness. Front pump seal leaks cause external fluid loss.

Question 6: A technician notices that transmission fluid on the dipstick appears dark brown/black and has a burnt smell. What does this indicate?

The fluid has been contaminated with engine coolant
Normal fluid color for high-mileage transmissions
Overheating has occurred, causing clutch material to burn and contaminate the fluid (Correct answer)
The fluid additive package has separated and is normal

Correct answer: Overheating has occurred, causing clutch material to burn and contaminate the fluid

Dark brown/black transmission fluid with a burnt smell indicates the fluid has overheated and clutch friction material has been burned. This is a serious condition that contaminates the fluid, damages clutch material, and may have caused permanent valve body and bearing damage.

Automatic transmission fluid (ATF) is normally a bright red color and has a slightly sweet smell when new. The fluid serves as a hydraulic medium, lubricant, and coolant for the transmission. Evaluating fluid condition during service provides valuable diagnostic information. Dark brown or black fluid with a burnt odor indicates thermal degradation of both the fluid itself and the friction (clutch) material. When a transmission overheats — due to towing heavy loads without a transmission cooler, low fluid level causing slippage and heat, or mechanical failure causing extended clutch slippage — the fluid breaks down. Oxidation turns the fluid dark and causes the additive package to deplete. More critically, the clutch friction material (bonded to the steel clutch plates) burns and sheds carbon particles into the fluid. These particles contaminate the entire hydraulic system, clogging the filter, scoring valve bores, wearing pump components, and further degrading any remaining friction surfaces. When this condition is found, simply changing the fluid is insufficient — the transmission requires a complete overhaul, including replacement of all friction elements, cleaning or replacement of the valve body, and flushing all fluid passages. The cause of overheating must also be corrected. Pink/milky fluid indicates coolant contamination from a failed cooler in the radiator. Normal aged fluid is typically orange or light brown without a burnt odor.

ASE Practice Test (A2: Automatic Transmission/Transaxle) 2

A customer complains that their automatic transmission slips only when cold and shifts normally once at operating temperature.
What is the MOST likely cause?