ASE H3 Drive Train (Transit Bus)

On a transit bus equipped with an Allison B-series automatic transmission, what is the primary function of the torque converter?

• ATo multiply engine torque hydraulically during acceleration and provide a fluid coupling
• BTo lock the engine directly to the output shaft at idle
• CTo engage the parking pawl when the bus is stopped
• DTo cool the transmission fluid before it returns to the sump

Technician A says the torque converter lockup clutch eliminates converter slip to improve fuel economy at cruising speed. Technician B says the lockup clutch should engage at or near stall for maximum torque multiplication. Who is correct?

• ATechnician B only
• BTechnician A only
• CBoth A and B
• DNeither A nor B

A transit bus automatic transmission uses planetary gearsets. Which component arrangement allows a single gearset to provide reduction, direct drive, or reverse depending on which member is held or driven?

• APressure plate, clutch disc, and flywheel
• BInput shaft, lay shaft, and synchronizer
• CSun gear, planet pinions/carrier, and ring gear
• DPinion gear, ring gear, and spider gears

On an Allison electronically controlled transit transmission, which device commands shift solenoids and clutch apply based on inputs such as throttle position, output speed, and range selection?

• AThe retarder modulation valve
• BThe output speed sensor reluctor ring
• CThe torque converter stator
• DThe transmission control module (TCM/ECU)

A transit bus shows a transmission fluid that is dark brown and smells burnt. What does this most likely indicate?

• AOverheated fluid with degraded friction-clutch material
• BNormal new-fluid color for synthetic transmission fluid
• CCoolant contamination from a failed heat exchanger
• DExcessive fluid level causing aeration

What is the correct procedure for checking the fluid level on most Allison transit bus transmissions equipped with a dipstick?

• ACheck cold immediately after a road test with the engine off
• BCheck with the fluid at operating temperature, engine idling, transmission in neutral or…
• CCheck with the engine off after the bus has sat overnight only
• DCheck at full throttle with the wheels chocked

Technician A says many heavy-duty transit transmissions specify a TES-certified synthetic transmission fluid for extended drain intervals. Technician B says any universal automatic transmission fluid is acceptable as long as the level is correct. Who is correct?

• ABoth A and B
• BTechnician B only
• CTechnician A only
• DNeither A nor B

A transit bus transmission goes into a fault mode and limits operation to a single forward range after logging a code. This protective behavior is best described as:

• AAdaptive shift learning
• BTorque converter stall test
• CNeutral lockout
• DLimp-home / do-not-shift mode

During a stall test on a transit bus automatic transmission, engine RPM is far below the specified stall speed. This most likely indicates:

• AEngine performance problem or stator one-way clutch slipping
• BA slipping forward clutch pack
• CExcessive line pressure
• DA stuck-on lockup clutch only at idle

What is the purpose of an integral hydraulic retarder in a transit bus automatic transmission?

• ATo increase engine output torque on grades
• BTo provide supplemental, brake-saving deceleration by absorbing energy in fluid
• CTo lubricate the planetary gearsets at high speed
• DTo replace the service brakes entirely during normal stops

A transit bus transmission overheats only when the integral retarder is used heavily on a long downgrade. The most likely cause is:

• ALow engine oil level
• BWorn driveshaft U-joints
• CRestricted transmission cooler or heat-exchanger flow
• DA faulty range selector switch

On an electronically controlled transit transmission, the turbine speed sensor signal is lost. The TCM will most likely:

• AIncrease line pressure to maximum permanently
• BEngage the parking pawl while driving
• CDisable the engine entirely
• DSet a fault code and use default or alternate shift logic, possibly limiting shifting

Which of the following best describes a clutch-to-clutch shift in a modern transit automatic transmission?

• AOne clutch releases as another applies, with overlap controlled electronically
• BA shift made by synchronizing two manual gears
• CA shift that uses a single band only
• DA shift performed only by the torque converter lockup clutch

A transit bus exhibits a delayed, harsh 1-2 upshift after a clutch overhaul. Diagnostics show the transmission has not relearned its shift adapts. The correct next step is to:

• AReplace the torque converter
• BPerform the TCM adaptive/clutch-fill relearn procedure
• CIncrease the fluid level above the full mark
• DDisconnect the output speed sensor

The transmission fluid temperature on a transit bus reaches the TCM's high-temperature threshold. A typical protective response is to:

• ADisable the speedometer
• BIncrease converter slip to generate more heat
• CApply the lockup clutch earlier and/or restrict range to reduce heat
• DOpen the parking pawl

What is the function of the stator in a transit bus torque converter?

• ATo drive the transmission input shaft directly
• BTo filter the transmission fluid
• CTo engage the parking pawl
• DTo redirect fluid returning from the turbine back to the impeller for torque multiplicati…

A transit bus has no upshift past first range and the malfunction lamp is on. A scan tool shows an output speed sensor circuit fault. Technician A says the TCM may inhibit upshifts because it cannot confirm vehicle speed. Technician B says this fault has no effect on shifting. Who is correct?

• ATechnician A only
• BTechnician B only
• CBoth A and B
• DNeither A nor B

During a hydraulic pressure test on a transit automatic transmission, main (line) pressure is low at all ranges. The most likely cause is:

• AA misadjusted parking pawl
• BA worn or aerated pump, internal leakage, or low fluid
• CWorn driveshaft slip yoke
• DA loose wheel bearing

A transit bus automatic transmission slips only in a specific range while other ranges are normal. The most likely cause is:

• ALow fluid level affecting all ranges equally
• BA worn universal joint
• CA failing clutch pack or seal in the circuit applied for that specific range
• DAn open transmission temperature sensor

What is the recommended action before condemning a transit bus transmission for a no-move condition in all ranges?

• AReplace the entire transmission immediately
• BRemove the rear drive axle
• CReplace only the driveshaft
• DVerify fluid level/condition, check for stored codes, and perform pressure and stall tests

A transit bus transmission produces a milky, pinkish fluid. This most likely indicates:

• ACoolant intrusion from a failed transmission oil cooler/heat exchanger
• BNormal aerated condition that clears with driving
• CCorrect synthetic fluid color
• DExcess additive package separation

On a transit bus, the transmission shifts erratically and the scan tool shows an intermittent throttle position input. The most appropriate diagnostic step is to:

• AReplace the torque converter
• BInspect wiring/connectors and verify the throttle/load signal source the TCM uses
• CReplace the drive axle
• DAdd fluid above the full line

Which statement about transit bus transmission prognostics features is correct?

• AThey predict the engine's fuel economy only
• BThey disable the bus after a set mileage
• CThey monitor fluid life, filter life, and clutch wear to schedule maintenance before fail…
• DThey replace the need for any fluid analysis

A transit bus transmission filter prognostic alert is active. The correct technician response is to:

• AIgnore it until the next annual service
• BReplace the drive axle seals
• CReplace the torque converter
• DInspect and replace the transmission filter and verify fluid condition

What is the most accurate way to verify transmission fluid temperature on a modern electronic transit transmission?

• AReading the transmission oil temperature parameter with a scan tool
• BTouching the transmission case by hand
• CEstimating from engine coolant temperature
• DChecking the color of the dipstick fluid

A transit bus will not move in forward ranges but reverse works normally. This points to a fault in:

• AThe output speed sensor
• BThe clutch/circuit common to forward ranges only
• CThe driveshaft center bearing
• DThe differential carrier bearings

Technician A says converter lockup clutch shudder can be caused by degraded or incorrect transmission fluid. Technician B says lockup shudder is always a failed torque converter that must be replaced first. Who is correct?

• ABoth A and B
• BTechnician B only
• CTechnician A only
• DNeither A nor B

During preventive maintenance on a transit bus, the technician finds the transmission breather/vent plugged. The likely consequence is:

• AImproved fluid filtration
• BLower fluid temperature
• CFaster lockup engagement
• DPressurized case causing seal leaks and possible fluid expulsion

A transit transmission exhibits a flared (engine RPM rises momentarily) 2-3 shift. The most likely cause is:

• ALate apply of the on-coming clutch (clutch fill/adapt or low circuit pressure)
• BA bent driveshaft
• CA worn pinion seal
• DA loose wheel lug

What does a transmission 'do-not-shift' light combined with a stored solenoid circuit code most likely indicate?

• ANormal operation with no required action
• BAn electrical fault in a shift-control solenoid circuit forcing a protective mode
• CLow engine oil pressure
• DA flat tire

On a transit bus automatic, which input does the TCM use to detect torque converter slip across the lockup clutch?

• AWheel speed only
• BCoolant temperature
• CThe difference between engine (impeller) speed and turbine speed
• DBrake pedal position only

A transit bus transmission has correct fluid level but the fluid is foamy on the dipstick. The most likely cause is:

• AA misaligned driveshaft
• BA worn ring gear
• CA failed U-joint
• DAir being drawn in at a loose suction-side connection or wrong fluid level history

When performing a hydraulic pressure test, the technician should always:

• AUse a gauge of correct range and follow the manufacturer's test points and procedure
• BUse any available gauge regardless of range
• CTest only with the engine off
• DDisable the speed sensors first

A transit bus has a complaint of harsh engagement when shifted from neutral to drive while parked. A likely cause is:

• AA worn driveshaft slip joint
• BExcessively high clutch apply pressure or stale neutral-to-drive adapt
• CA leaking axle breather
• DA loose wheel bearing

Technician A says a transmission oil cooler (heat exchanger) leak can allow transmission fluid to enter the engine cooling system. Technician B says it can also allow coolant into the transmission. Who is correct?

• ATechnician A only
• BTechnician B only
• CBoth A and B
• DNeither A nor B

A transit transmission shows the correct hot fluid level when checked, but customers report a low-fluid warning intermittently. The best diagnostic step is to:

• AAdd a quart of fluid regardless
• BReplace the differential
• CReplace the driveshaft
• DUse the scan tool oil level sensor data and verify level at the specified temperature and…

What is the correct interpretation of a transmission oil life prognostic reaching 0%?

• ARecommended fluid service interval has been reached based on monitored duty cycle
• BThe transmission has failed and must be replaced
• CThe torque converter is locked on
• DThe engine must be replaced

A transit bus loses all forward and reverse movement and the scan tool shows extremely low main pressure. After confirming proper fluid level, the next likely cause to investigate is:

• AA worn U-joint
• BThe transmission charging pump or pressure regulator valve
• CA bent axle shaft
• DA loose lug nut

On a transit bus, the retarder applies weakly and slowly even at full request. With no stored codes, a likely mechanical cause is:

• AA worn ring and pinion
• BA bad output speed sensor
• CLow transmission fluid or restricted retarder accumulator/charge circuit
• DAn open brake light switch

Which condition would most likely cause a transit transmission to default to a fixed range and illuminate the warning lamp immediately at start-up?

• AA normal cold start
• BA clean air filter
• CSlightly low tire pressure
• DA range selector or shift-selector circuit fault detected on power-up

A transit bus customer reports the transmission upshifts too early under load, causing sluggish acceleration. With normal fluid, the technician should first:

• AVerify the throttle/load signal and shift schedule data with a scan tool
• BReplace the transmission
• CReplace the driveshaft
• DReplace the wheel bearings

What is the main risk of operating a transit bus transmission with the fluid level significantly below the full mark?

• AImproved cooling
• BPump cavitation, aeration, slipping clutches, and overheating
• CFaster lockup engagement
• DLower line pressure is harmless

A transit transmission has a chronic high fluid temperature even in moderate service with no retarder use. After verifying correct fluid level and type, the technician should inspect:

• AThe axle vent
• BThe driveshaft balance weights
• CThe cooler circuit flow, heat exchanger condition, and coolant system
• DThe wheel seal

Technician A says clearing transmission diagnostic codes without repairing the cause will permanently fix the problem. Technician B says codes should be diagnosed and the root cause corrected before clearing. Who is correct?

• ATechnician A only
• BNeither A nor B
• CBoth A and B
• DTechnician B only

A transit bus exhibits a neutral condition (engine revs, no drive) only when the transmission fluid is hot. The most likely cause is:

• AA clutch or seal that loses sealing/capacity as fluid thins with heat
• BA cold-start enrichment fault
• CA loose battery terminal
• DA worn brake shoe

During a transmission service on a transit bus, why is it important to replace the internal filter and clean any magnets?

• ATo increase fluid temperature
• BTo remove accumulated wear debris and maintain proper filtration and fluid health
• CTo disable the prognostics
• DTo increase converter slip

A transit bus has a delayed forward engagement (several seconds) after sitting overnight, then operates normally. The most likely cause is:

• AA worn driveshaft
• BA bad output speed sensor
• CFluid draining back from the circuit/converter, plus a leaking check or seal allowing slo…
• DA misadjusted parking brake