ASNT NDT Level II Radiographic Testing (RT)

Correct: High line pressure and harsh shifting often result from the Electronic Pressure Control (EPC) system failing to regulate pressure downward. If the filter screen for the EPC solenoid is restricted, the solenoid cannot effectively bleed off pressure to the sump, causing the pressure regulator valve to default to maximum line pressure as a fail-safe measure to prevent clutch slippage.

Incorrect: Focusing on the torque converter clutch solenoid is incorrect because a TCC solenoid stuck on typically causes the engine to stall when coming to a stop in gear, rather than causing high line pressure or harsh upshifts. The strategy of blaming a leaking input shaft seal is flawed because internal leaks generally lead to low pressure, slipping, or delayed engagement, which is the opposite of the high-pressure, harsh-shift symptom described. Attributing the issue to a worn planetary gear set is unlikely because mechanical gear wear usually manifests as noise, vibration, or a complete loss of a specific gear ratio, not a systemic increase in hydraulic line pressure across all forward gears.

Takeaway: Restricted EPC solenoid filters often cause high default line pressure, leading to harsh shifts without necessarily triggering electronic fault codes.

Correct: Worn or broken transmission or engine mounts allow the powertrain to rotate excessively under torque. This movement causes the clunking noise as the assembly hits its travel limit or contacts the vehicle frame. Loading the drivetrain while holding the brakes allows a technician to safely observe this movement and identify which specific mount has failed or separated.

Incorrect: Focusing only on hydraulic line pressure ignores the physical movement observed during the torque test. The strategy of checking U-joints addresses driveline noise but does not explain the excessive engine and transmission lift seen in the engine bay. Choosing to re-index the torque converter is an attempt to fix a rotational vibration issue rather than a mounting-related clunk or physical displacement.

Takeaway: Excessive powertrain movement during gear engagement typically indicates a failed mount that has lost its ability to isolate torque and movement.

Correct: The stator is positioned between the impeller and the turbine. During acceleration, when there is a large difference in speed between the impeller and turbine, the stator’s one-way clutch locks it to a stationary reaction shaft. This allows the stator vanes to redirect the fluid returning from the turbine so that it strikes the impeller vanes in the direction of engine rotation, which multiplies the torque produced by the engine.

Incorrect: Suggesting the turbine increases its speed relative to the input shaft is incorrect because the turbine is mechanically splined to the transmission input shaft and must rotate at the same speed. The strategy of the impeller bypassing the stator assembly is physically impossible in a standard torque converter design, as fluid must pass through the stator to return to the impeller. Opting for the lock-up clutch as the source of torque multiplication is a common misconception, as the lock-up clutch actually eliminates slip and torque multiplication to provide a direct 1:1 mechanical drive for better fuel efficiency.

Takeaway: The stator multiplies torque by redirecting fluid flow back to the impeller while held stationary by its one-way clutch.

Correct: When a torque converter fails to achieve a full mechanical lock-up despite being commanded to do so, the difference in speed between the impeller and turbine results in slip. This slip generates significant internal friction within the transmission fluid, converting power into heat rather than mechanical work. This process reduces the overall efficiency of the powertrain and causes the transmission fluid to oxidize more rapidly due to the elevated temperatures.

Incorrect: The idea that slip provides beneficial torque multiplication at highway speeds is incorrect because torque multiplication is only significant at high stall ratios and diminishes as the turbine speed nears the impeller speed. Suggesting that slip improves cooling efficiency is a fundamental misunderstanding of thermodynamics, as the slip itself is the primary source of heat generation. Attributing the slip to a necessary dampening effect for the gear sets ignores the fact that the lock-up clutch is specifically engineered to eliminate slip at cruising speeds to meet fuel economy standards.

Takeaway: Unintended torque converter slip at cruising speeds causes parasitic energy loss as heat, leading to decreased fuel efficiency and fluid breakdown.

Correct: When the Transmission Control Module (TCM) detects a failure in a critical input sensor such as the Throttle Position Sensor (TPS) or Mass Air Flow (MAF) sensor, it can no longer accurately calculate engine load. To protect the internal friction elements from slipping and burning, the TCM defaults to a fail-safe mode. In many systems, this involves commanding the EPC solenoid to a state that results in maximum line pressure, which manifests as a fixed, non-varying duty cycle on the scan tool and results in noticeably harsh shifts.

Incorrect: Attributing the fixed duty cycle to a high-temperature condition is incorrect because the TCM would typically increase cooling flow or alter shift points rather than fixing the pressure at a single fail-safe value. Suggesting that a torque converter clutch solenoid failure would lock line pressure at a minimum value is inaccurate, as TCC faults generally affect engine stalling or vibration rather than overriding the primary pressure control logic. The strategy of assuming a mechanically stuck shift solenoid would cause a fixed EPC duty cycle is also flawed, as the TCM monitors electrical circuits and would likely set a specific shift solenoid code without necessarily defaulting the entire pressure control system to a fixed output unless a total limp-in mode was triggered.

Takeaway: A fixed EPC solenoid duty cycle during varying load conditions typically indicates the TCM has entered a high-pressure fail-safe mode due to lost inputs.

Correct: In many common automatic transmission architectures used in the United States, a specific brake band is utilized to hold a drum stationary to achieve both second and fourth gear ratios. If the friction material on this band is worn beyond limits or if the hydraulic servo piston seals are leaking, the band will not apply with enough force to hold the drum, leading to slipping specifically in those two gear ranges while leaving others unaffected.

Incorrect: Attributing the slipping to a failed stator one-way clutch is incorrect because a stator failure typically results in poor acceleration from a stop due to a lack of torque multiplication but does not cause gear-specific slipping. Suggesting excessive clearance in the forward clutch pack is inaccurate because the forward clutch is generally applied in all forward gears; a failure here would typically cause slipping in first gear or a total loss of forward movement. Focusing on a restricted oil cooler line is misplaced as this condition usually leads to transmission overheating and fluid foaming rather than the failure of specific gear ratios.

Takeaway: Slipping that occurs only in specific gear pairs often indicates a failure of a shared mechanical component like a band or servo.

Correct: In a standard high-speed CAN bus system, two 120-ohm termination resistors are wired in parallel at the ends of the bus, resulting in a total circuit resistance of 60 ohms. Measuring this resistance at the Data Link Connector (typically pins 6 and 14) with the battery disconnected allows the technician to verify that the wiring and resistors are physically intact without electrical interference.

Incorrect: Searching for full battery voltage on communication lines is an incorrect diagnostic approach because CAN bus systems operate on a low-voltage differential signal, usually biased at 2.5 volts. Focusing on hydraulic pressure tests is inappropriate for addressing ‘U’ series codes, which specifically indicate electronic communication failures rather than mechanical or hydraulic issues. The strategy of jumping communication wires together is dangerous and can lead to short circuits that destroy multiple control modules across the vehicle network.

Takeaway: Measuring 60 ohms of resistance across the CAN bus pins at the DLC verifies the physical integrity of the network wiring and resistors.

Correct: Inboard CV joints, which are typically tripod designs, allow for the linear movement or plunge of the axle as the suspension travels. When the internal housing or rollers of an inboard joint become worn, the torque applied during acceleration forces the rollers into worn pockets, creating a side-to-side shudder or vibration that ceases once the load is removed.

Incorrect: Focusing on the outboard Rzeppa joint is generally incorrect for this symptom because those joints typically manifest failure through a distinct clicking noise during sharp turns rather than a shudder under straight-line acceleration. Attributing the vibration to a seized intermediate shaft bearing is less likely as bearing failures usually produce a constant growl or whining noise that varies with vehicle speed regardless of engine load. The strategy of blaming an out-of-balance tire is flawed because tire-related vibrations are speed-sensitive and would persist even when coasting or during deceleration.

Takeaway: Inboard CV joints typically cause vibrations under acceleration, whereas outboard CV joints cause clicking noises during tight turns.

Correct: When a TCM detects a major electrical failure, it typically de-energizes the shift solenoids, which causes the transmission to default to a specific gear, such as second or third, depending on the design. Additionally, the pressure control solenoid defaults to a position that provides maximum line pressure to ensure that the friction elements are fully applied and do not slip under load.

Incorrect: Suggesting the transmission defaults to neutral is incorrect because the primary purpose of a limp-in mode is to allow the driver to move the vehicle to a safe location or service facility. Proposing that the torque converter clutch stays engaged is inaccurate because the TCM usually disables lock-up functions during fail-safe operation to prevent the engine from stalling when the vehicle comes to a stop. Assuming the system uses a mechanical governor is wrong because modern electronically controlled transmissions rely on electronic speed sensors and software logic rather than backup mechanical components for shifting.

Takeaway: Fail-safe mode protects the transmission by providing a fixed gear and maximum hydraulic pressure when electronic control is lost or compromised.

Correct: The Ravigneaux gear set is a specific compound planetary arrangement that features two sun gears of different sizes and a single common ring gear. This design is unique because it uses a single planet carrier to house two different sets of planet pinions, allowing for multiple gear ratios in a very compact space.

Correct: The stator is designed to redirect fluid flow back to the impeller to multiply torque during the stall and acceleration phases. For this to occur, the stator one-way clutch must lock to prevent the stator from rotating backwards. If the clutch slips or fails to lock, torque multiplication cannot happen, resulting in poor low-speed acceleration and a lower-than-normal stall speed.

Incorrect: The strategy of blaming a permanently engaged lock-up clutch is incorrect because this would typically cause the engine to stall when the vehicle comes to a stop, similar to a manual transmission car left in gear. Attributing the issue to stripped turbine splines is inaccurate as this would generally result in a complete loss of power transfer to the input shaft in all scenarios. Focusing on impeller cavitation due to low fluid levels is also incorrect because while it causes performance issues, it usually results in a higher-than-normal stall speed and slipping across the entire power band rather than just during initial acceleration.

Takeaway: A stator one-way clutch that fails to lock prevents torque multiplication, causing poor off-the-line acceleration and low stall speeds.

Correct: In most automatic transaxle hydraulic circuits, the fluid used for lubrication and cooling is sourced from the return side of the torque converter and the external oil cooler. If the cooler or its return line is restricted, the volume of oil reaching critical bushings and the final drive is severely diminished, even if the main line pressure remains at the specified level. This restriction also prevents heat from being dissipated from the torque converter, leading to the overheating symptoms described.

Incorrect: Focusing only on the main pressure regulator valve is incorrect because a fault in this component would typically manifest as high or low line pressure readings during the initial gauge test. Attributing the failure to a worn oil pump rotor set is unlikely since a pump with excessive clearance would generally fail to maintain adequate line pressure, especially when the fluid is hot. The strategy of inspecting the forward clutch piston seal is misplaced because a leak in that specific circuit would cause engagement issues or slippage in forward gears rather than a systemic lubrication and cooling failure.

Takeaway: Lubrication and cooling flow often depend on the integrity of the cooler circuit rather than just the main line pressure.

Correct: The scan tool data indicates that the electronic control side is functioning because the module is recognizing the need for a shift and sending the command. By performing a bidirectional actuator test, the technician can bypass the normal operating logic to directly trigger the solenoids. This allows for the isolation of the problem to either a faulty solenoid, a hydraulic leak in the valve body, or a mechanical failure within the clutch pack by observing how the system responds to a direct command.

Incorrect: The strategy of replacing the control module is premature because the live data confirms the module is successfully processing inputs and generating the correct output commands. Simply clearing adaptive learning values is unlikely to resolve a multi-second delay, as these values are intended for fine-tuning shift feel rather than correcting major timing discrepancies. Focusing only on engine sensors like the throttle or coolant temperature is unnecessary in this scenario because the data stream has already confirmed that the transmission controller is receiving the necessary information to initiate the shift command at the appropriate time.

Takeaway: When a control module commands an action that does not occur, use bidirectional tests to isolate hydraulic or mechanical failures from electronic commands.

Correct: Proper phasing involves aligning the yokes at each end of the shaft in the same plane. This configuration ensures that the non-uniform velocity produced by the first universal joint is cancelled out by the second universal joint, preventing harmonic driveline vibrations.

Incorrect: Relying on the orientation of grease fittings for balance is incorrect as fittings are typically positioned for accessibility rather than primary rotational balancing. The strategy of fully seating the slip yoke against the transmission seal is dangerous because it leaves no room for the driveshaft to move as the suspension compresses. Choosing to apply grease to the external surface of the slip yoke is unnecessary and can attract road debris, which may damage the output shaft seal over time.

Takeaway: Proper driveshaft phasing ensures that velocity changes in one universal joint are cancelled by the other, preventing harmonic vibrations.

Correct: A leaking or hardened piston lip seal allows hydraulic fluid to escape the apply circuit, which prevents the piston from exerting full clamping force on the clutch pack. This insufficient pressure leads to friction disc slippage during torque transfer, creating the extreme heat necessary to glaze the friction material and discolor the steel plates.

Incorrect: Attributing the damage to a restricted oil cooler is incorrect because this would typically cause generalized overheating and fluid degradation rather than damage isolated to a single clutch pack. The strategy of blaming an incorrectly installed one-way sprag clutch is flawed as this would usually result in a complete loss of specific gears or mechanical binding rather than gradual slipping. Relying on a faulty engine coolant temperature sensor as the primary cause is unlikely because the transmission control module would generally default to maximum line pressure in the event of a sensor failure to protect the clutches.

Correct: The Input Speed Sensor (ISS), or turbine speed sensor, is vital for the TCM to calculate torque converter slip and verify gear ratios. When the ISS signal is lost, the TCM can no longer accurately monitor clutch application or slippage. To prevent catastrophic failure of the friction elements, the TCM typically defaults to a fail-safe mode that commands maximum line pressure to ensure firm clutch engagement and disables the torque converter clutch (TCC) to prevent engine stalling or erratic operation.

Incorrect: The strategy of using engine coolant temperature as a substitute is incorrect because temperature data cannot provide the rotational speed information required to calculate gear ratios or slip. Focusing only on lowering line pressure is a dangerous misconception; low pressure during a sensor failure would lead to rapid clutch slippage and burnt friction material rather than protection. Choosing to shift the transmission into neutral is not a standard fail-safe strategy for speed sensor loss, as manufacturers design these systems to allow the vehicle to be driven to a repair facility in a specific ‘limp’ gear.

Takeaway: Loss of the Input Speed Sensor signal typically triggers a high-pressure fail-safe mode to prevent clutch slippage and internal damage.

Correct: Back-probing the connector while the circuit is active allows the technician to perform a voltage drop test, which is the most effective way to identify high resistance or circuit failures under actual load. This method ensures that the TCM is successfully completing the circuit and that the wiring can support the necessary current flow to actuate the solenoid, confirming the electrical path is functional.

Incorrect: Measuring resistance while the ignition is ON or the circuit is powered can lead to incorrect readings and may damage the multimeter. Relying on a test light connected to battery positive to probe TCM drivers is risky because the current draw of the bulb might exceed the rating of the solid-state drivers in the module. Checking for continuity to ground during engine cranking is an inappropriate diagnostic step that does not simulate the actual operating conditions of the shift solenoid and provides no useful data regarding its performance.

Takeaway: Dynamic voltage drop testing while the circuit is under load is the most reliable method for identifying electrical faults in transmission solenoids.

Correct: A mechanical line pressure test is the definitive diagnostic procedure to verify if the hydraulic system is generating and regulating pressure according to manufacturer specifications. This test confirms whether the pump and regulator valve are responding correctly to increased engine load, ensuring there is sufficient clamping force on the clutches and bands to prevent slippage during high-torque conditions.

Incorrect: Choosing to replace the electronic pressure control solenoid without testing is an inefficient diagnostic practice that may not address a mechanical pump failure or internal leak. The strategy of resetting adaptive memory only modifies software-learned values and cannot compensate for a physical loss of hydraulic pressure. Focusing only on the wiring harness assumes an electrical fault exists when the problem could be a mechanical wear issue in the pump or regulator valve.

Takeaway: Mechanical line pressure testing is the primary diagnostic step for identifying hydraulic regulation issues that cause clutch slippage under load.

Correct: To achieve a reverse gear ratio in a simple planetary gear set, one member must be the input, one must be the output, and one must be held stationary. When the sun gear is the input and the planetary carrier is held stationary, the planet gears act as idlers, causing the ring gear to rotate in the opposite direction of the sun gear, which provides the reverse direction.

Incorrect: The strategy of holding the ring gear stationary while the sun gear is the input results in a forward gear reduction rather than reverse. Locking two members of the gear set together results in a direct drive ratio of 1:1 where the entire assembly rotates as a single unit in the same direction. Choosing to use the planetary carrier as the input while holding the sun gear stationary results in a forward overdrive ratio.

Takeaway: Holding the planetary carrier stationary in a simple planetary gear set creates a reverse gear output when the sun gear is driven as the input member.

Correct: In modern electronically controlled AWD systems, the transfer case uses a clutch pack to distribute torque between the front and rear axles. During tight turns, the front and rear axles must rotate at different speeds to prevent driveline wind-up. The control module should monitor inputs like the steering angle sensor and vehicle speed to reduce the duty cycle (pulse-width modulation) to the clutch solenoid, allowing the plates to slip. If the module maintains a high duty cycle, the axles stay locked together, causing the binding sensation described.

Incorrect: The theory regarding a viscous coupling fluid leak is incorrect because a loss of silicone fluid typically results in a lack of torque transfer to the secondary axle rather than a locked condition. Suggesting a sheared sun gear is inaccurate as this mechanical failure would generally cause a complete loss of drive or significant noise rather than binding during turns. Attributing the issue to the main transaxle forward clutch is a misunderstanding of the system architecture, as that clutch manages the connection between the engine and the gear train, not the speed differential between the front and rear axles.

Takeaway: AWD binding during tight turns usually indicates the transfer case is failing to allow the necessary speed differential between axles during maneuvers.