Chevrolet Silverado / GMC Sierra. Manual — part 832
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
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
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.
Lightly tap and release the brake pedal. The TCC will release on most applications.
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 following conditions:
The TCC releases.
The transmission downshifts immediately to FIFTH range.
MANUAL DOWNSHIFTS
1. Place the shift selector in DRIVE.
2. Accelerate the vehicle to obtain SIXTH range.
IMPORTANT: The TCC will not engage until the engine is in closed loop
operation. The vehicle must be in a near cruise condition, not
accelerating or coasting, and on a level road surface.
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
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 TCC releases.
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 TCC releases.
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 following conditions:
The TCC releases.
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
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
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.
TORQUE CONVERTER DIAGNOSIS
The torque converter clutch (TCC) is applied by fluid pressure, which is controlled through the
converter flow valve by the TCC variable bleed solenoid. The converter flow valve and the TCC
variable bleed solenoid are located inside the automatic transmission assembly.
TORQUE CONVERTER STATOR
The torque converter stator assembly can have 2 different malfunctions.
The stator assembly freewheels in both directions.
The stator assembly remains locked up at all times.
POOR ACCELERATION AT LOW SPEED
If the stator is freewheeling at all times, the car tends to have poor acceleration from a standstill.
At speeds above 50-55 km/h (30-35 mph), the car may perform normally. For poor acceleration,
you should first determine that the exhaust system is not blocked, and the transmission is in
FIRST range when starting out.
If the engine freely accelerates to a high RPM in NEUTRAL, you can assume that the engine and
the exhaust system are normal. Inspect for poor performance in DRIVE and REVERSE in order
to help determine if the stator is freewheeling at all times.
POOR ACCELERATION AT HIGH SPEED
If the stator is locked up at all times, performance is normal when accelerating from a standstill.
Engine RPM and vehicle speed are limited or restricted at high speeds. Visual examination of the
converter may reveal a blue color caused by overheating.
You should be able to turn the race clockwise, but should have difficulty in moving the race
counterclockwise, or you may be unable to move the race at all.
WHINE NOISE
IMPORTANT: Do not confuse this noise with pump whine noise, which is
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
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