Allison - Automatic Transmission
Road Test
Note: The Road Test Procedure should be performed only as part of the Functional Test Procedure. Refer to Functional Test (Functional Test).
The following test provides a method of evaluating the condition of the automatic transmission. The test is structured so that most driving conditions would be achieved. The test is divided into the following parts:
* Electrical Function Check
* Upshift Control and Torque Converter Clutch (TCC) Apply
* Part Throttle Detent Downshifts
* Full Throttle Detent Downshifts
* Manual Downshifts
* Coasting Downshifts
* Manual Range Selection
- REVERSE
- Manual FIRST
Note: Complete the test in the sequence given. Incomplete testing cannot guarantee an accurate evaluation.
Before the road test, ensure the following conditions are met:
* The engine is performing properly.
* Transmission fluid level is correct.
* Tire pressure is correct.
During the road test:
* Perform the test only when traffic conditions permit.
* Operate the vehicle in a controlled, safe manner.
* Observe all traffic regulations.
* View the scan tool data while conducting this test.
Take along qualified help in order to operate the vehicle safely.
* Observe any unusual sounds or smells.
After the road test, inspect the following conditions:
* Transmission fluid level
Refer to Transmission Fluid Level and Condition Check (Transmission Fluid Level and Condition Check).
* Diagnostic trouble codes (DTCs) that may have set during the testing
Refer to the applicable DTC.
* Scan tool data for any abnormal readings or data
Electrical Function Check
Perform this check first, in order to ensure the electronic transmission components are connected and functioning properly. If these components are not checked, a simple electrical condition could be mis-diagnosed.
1. Install the scan tool.
2. Ensure the shift selector is in PARK and set the parking brake.
3. Start the engine.
4. Verify that the following scan tool data can be obtained and is functioning properly. Refer to Control Module References (Control Module References) for scan tool information. Data that is questionable may indicate a concern.
* Engine speed
* Transmission input speed
* Transmission turbine speed
* Transmission output speed
* Vehicle speed
* TFP 1, 2, 3 and TFP 4 pressure switch states
* C, D, E and REVERSE pressure switch states
* Transmission range, engine list
* 4WD low
* Commanded range, current range
* PCS1 and PCS2 solenoid reference current
* PCS1 and PCS2 solenoid actual current
* PCS1 and PCS2 solenoid duty cycle
* Brake switch
* Engine coolant temperature
* Transmission fluid temperature
* Throttle angle
* Ignition voltage
* Shift solenoid 1
* Shift solenoid 2
* Shift solenoid 3
* Modulated main G solenoid
* TCC solenoid duty cycle
* TCC slip speed
5. Monitor the brake switch signal while depressing and releasing the brake pedal. The scan tool should display the following:
* Closed when the brake pedal is released
* Open when the brake pedal is depressed
6. Check the garage shifts.
1. Apply the brake pedal and ensure the parking brake is set.
2. Move the shift selector through the following ranges:
1. PARK to REVERSE
2. REVERSE to NEUTRAL
3. NEUTRAL to DRIVE
3. Pause 2 to 3 seconds in each selector position.
Note: Harsh or soft engagement may be caused by any of the following conditions:
* High idle speed
Compare engine idle speed to desired idle speed.
* Incorrect PCS1 or PCS2 solenoid current
Compare PCS1 and PCS2 solenoid reference current to PCS1 and PCS2 solenoid actual current.
* Slow moving or sticking logic valves
* Shift is not fully adapted
* Low fluid level
* Cold transmission fluid
Inspect for low transmission fluid temperature.
4. Verify the range engagements are immediate and not harsh.
7. Monitor the transmission range on the scan tool engine list.
1. Apply the brake pedal and ensure the parking brake is set.
2. Move the shift selector through all ranges.
3. Pause 2 to 3 seconds in each range.
4. Return the shift selector to PARK.
5. Verify that all of the selector positions match the scan tool display.
8. Inspect the throttle angle input.
1. Apply the brake pedal and ensure the parking brake is set.
2. Ensure the shift selector is in PARK.
3. Monitor the throttle angle while increasing and decreasing the engine speed with the throttle pedal. The scan tool throttle angle should increase and decrease with the engine speed.
If any of the above checks do not perform properly, record the result for reference after the completion of the Road Test Procedure.
Upshift Control and Torque Converter Clutch (TCC) Apply
The transmission control module (TCM) calculates the upshift points based on the throttle angle and the engine, turbine and output speed. When the TCM determines that conditions are met for a shift to occur, the TCM commands the shift, and controls PCS1 and PCS2 solenoid current to proper control clutch pressures during the shift.
Perform the following steps:
1. Choose a throttle position of 10 percent, 25 percent or 50 percent. All throttle angles shown should be tested to cover the normal driving range.
2. Monitor the following scan tool parameters:
* Throttle angle
* Vehicle speed
* Engine speed
* Turbine speed
* Output shaft speed
* Commanded range
* Slip speed
* Solenoid states
3. Place the shift selector in DRIVE.
4. Using the chosen throttle angle, accelerate the vehicle. Hold the throttle steady.
5. As the transmission upshifts, note the vehicle speed when the shift occurs for each range change. There should be a noticeable shift feel or engine speed change within 1 to 2 seconds of the commanded range change.
6. Shift speeds may vary slightly due to transmission fluid temperature or hydraulic delays in responding to the electronic controls.
* Note any harsh, soft or delayed shifts or slipping.
* Note any noise or vibration.
7. Repeat steps 1-6 to complete all throttle angles.
8. Inspect for TCC apply in SECOND, THIRD, FOURTH, FIFTH and SIXTH range. Note the TCC apply point. When the TCC applies there should be a noticeable drop in engine speed and a drop in slip speed to below 100 RPM. If the TCC apply can not be detected inspect for DTCs. Refer to Torque Converter Diagnosis (Torque Converter Diagnosis).
Part Throttle Detent Downshift
1. Place the shift selector in DRIVE.
2. Accelerate the vehicle to a speed just above the FIFTH to SIXTH shift point, using less than 50 percent throttle.
3. Quickly increase throttle angle to greater than 63 percent.
4. Verify the transmission downshifts immediately to FIFTH range.
Manual Downshifts
1. Place the shift selector in DRIVE.
2. Accelerate the vehicle to obtain SIXTH range.
3. Place the shift selector in RANGE SELECTION MODE (M).
4. By pressing the "+/-" button on the shift selector select the desired preselect range.
5. Release the throttle.
6. Verify the following conditions:
* The transmission downshifts immediately to the preselected range. Downshifts will occur in sequence to the preselect range.
* The engine slows the vehicle.
Manual 2-1 Downshift
1. Place the shift selector in DRIVE.
2. Accelerate the vehicle until the 1-2 shift occurs.
3. Go to 8 km/h (5 mph) above the 1-2 shift point.
4. Release the throttle while moving the shift selector to FIRST.
5. Verify the following conditions:
* The transmission immediately downshifts to FIRST range.
* The engine slows the vehicle.
Coasting Downshifts
1. Place the shift selector in DRIVE.
2. Accelerate the vehicle to SIXTH range with the TCC applied.
3. Release the throttle and lightly apply the brakes.
4. Verify the downshifts occur in normal sequence and the transmission returns to FIRST range before the vehicle comes to a stop.
Manual Range Selection
The shift solenoids control the upshifts in the manual ranges.
Perform the following tests, using 10-15 percent throttle angle.
REVERSE
1. With the vehicle stopped, move the shift selector to REVERSE.
2. Slowly accelerate the vehicle.
3. Verify that there is no noticeable slip, noise or vibration.