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Chevrolet Silverado / GMC Sierra. Manual - part 1003
THIRD RANGE
Before making the shift from second to third range, the transmission control module (TCM)
makes certain all of the shift valves are in the correct position with shift valve 1, shift valve 2, and
shift valve 3 de-stroked.
Pressure control solenoid 2 (PCS2) is de-energized, exhausting PCS2 signal pressure which
allows the pressure control valve 2 to de-stroke, exhausting the 2-6 clutch. PCS1 is de-energized,
raising PCS1 signal and PCS1 pressures. The PCS1 pressure is directed through shift valve 2 to
the 3rd, 5th, and reverse clutch. The TCM reduces current to PCS1, which controls the rate at
which the pressure control valve 1 supplies pressure to the 3rd, 5th, and reverse clutch, and
reduces current to PCS2, which controls the rate at which pressure control valve 2 exhausts the 2-
6 clutch, assuring a smooth transition to third range. Main pressure continues to flow through shift
solenoid 3 (SS3) and the manual selector valve to the 1-2-3-4 clutch, keeping the clutch applied.
The combination of the 1-2-3-4 clutch and the 3rd, 5th, and reverse clutch application produces
third range operation.
After the shift into third range is complete, SS1 is energized and directs control main pressure to
the top of shift valve 1, stroking the valve. With shift valve 1 in the stroked position, the 2-6
clutch feed is exhausted through shift valve 1 to exhaust backfill keeping the 2-6 clutch released
and the 4-5-6 clutch has an exhaust path through shift valve 1 to pressure control valve 2, keeping
the 4-5-6 clutch released.
Pressure switch 1 turns ON, providing feedback that shift valve 1 is stroked. Pressure switch 2
and pressure switch 3 remain OFF, providing feedback that shift valve 2 and shift valve 3 are in
the de-stroked position.
If electrical power is interrupted while the transmission is in third range, SS1 and the torque
converter clutch (TCC) solenoid (if TCC is applied) are de-energized. Shift valve 1 de-strokes,
changing the exhaust path of the 4-5-6 clutch to exhaust backfill and the exhaust path of the 2-6
clutch to pressure control valve 2. Normally closed PCS1 continues to block the exhaust of the
PCS1 signal pressure (signal remains control main). The signal pressure on top of pressure control
valve 1 produces maximum PCS1 pressure, which is routed through shift valve 2 to the 3rd, 5th,
and reverse clutch, keeping the clutch applied. With the manual selector valve in a forward
position, main pressure continues to feed the 1-2-3-4 clutch through shift valve 3 and the manual
selector valve. The combination of the 1-2-3-4 clutch and the 3rd, 5th, and reverse clutch applied
keeps the transmission in third range for limp home capability. If the TCC is applied, the TCC
solenoid de-energizes, causing the TCC valve to de-stroke, exhausting pressure from the top of
the converter flow valve. The converter flow valve de-strokes, redirecting main overage to
converter in and converter out to the cooler. The TCC is now released.
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
If electrical power is interrupted while the transmission is in third range, and the manual selector
valve is moved to Neutral (N), the 1-2-3-4 clutch exhausts through the manual selector valve to
exhaust backfill. The 3rd, 5th, and reverse clutch remains applied. With only one clutch applied,
the transmission goes to Neutral (N).
If electrical power is interrupted while the transmission is in third range and the manual selector
valve is moved to the Reverse (R) position, the 1-2-3-4 clutch exhausts through the manual
selector valve which releases the clutch. Main pressure goes through shift valve 3, the manual
selector valve and shift valve 2 to the low and reverse clutch, applying the clutch. The
combination of the 3rd, 5th, and reverse clutch and the low and reverse clutch application
produces Reverse (R) range for limp home capability.
Fig. 526: Identifying Hydraulic Circuits Used In Third Range
Courtesy of GENERAL MOTORS CORP.
FOURTH RANGE
Before making the shift from third to fourth range, the transmission control module (TCM) makes
certain all of the shift valves are in the correct position, with shift valve 1 stroked and shift valve
2 and shift valve 3 de-stroked.
Pressure control solenoid 1 (PCS1) is energized, opening the PCS1 signal pressure to exhaust
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
which allows the pressure control valve 1 to de-stroke and the 3rd, 5th, and reverse clutch
pressure is exhausted. PCS2 is energized, raising the PCS2 signal and PCS2 pressures. The PCS2
pressure is directed through shift valve 1, shift valve 3, shift valve 2, and the manual selector
valve to the 4-5-6 clutch, applying the clutch. Main pressure continues to flow through shift valve
3 and the manual selector valve to the 1-2-3-4 clutch, keeping the 1-2-3-4 clutch applied. The
TCM supplies current to PCS2, which controls the rate at which pressure control valve 2 supplies
pressure to the 4-5-6 clutch, and current to PCS1, which controls the rate at which pressure
control valve 1 exhausts the 3rd, 5th, and reverse clutch, assuring a smooth transition to fourth
range.
The combination of the 1-2-3-4 clutch and the 4-5-6 clutch application produces fourth range
operation.
After the shift to fourth range is completed, SS3 is energized, directing control main pressure to
the top of shift valve 3, stroking the valve. In the stroked position, main pressure is redirected
through shift valve 2 and the manual selector valve to the 4-5-6 clutch, keeping the 4-5-6 clutch
applied. The flow from pressure control valve 2 to shift valve 3 is directed through the manual
selector valve to the 1-2-3-4 clutch, keeping the 1-2-3-4 clutch applied.
Pressure switch 3 turns ON and pressure switch 1 remains ON, providing feedback that the valves
are stroked. Pressure switch 2 remains OFF, providing feedback that shift valve 2 is in the de-
stroked position.
If electrical power is interrupted while the transmission is in fourth range, PCS1, PCS2, the
torque converter clutch (TCC) solenoid, SS1, and SS3 are de-energized. Main pressure continues
to flow through shift valve 3 and shift valve 2 and the manual selector valve to the 4-5-6 clutch,
keeping the 4-5-6 clutch applied. When de-energized, normally open PCS2 exhausts the PCS2
signal pressure, allowing pressure control valve 2 to de-stroke and the 1-2-3-4 clutch exhausts.
After shift valve 1 de-strokes, the 1-2-3-4 clutch exhausts to exhaust backfill. Normally closed
PCS1 blocks the exhaust of PCS1 signal pressure, allowing the PCS1 signal and PCS1 pressures
to rise. Pressure control valve 1 directs full pressure through shift valve 2 to the 3rd, 5th, and
reverse clutch, applying the clutch. The combination of the 4-5-6 clutch and the 3rd, 5th, and
reverse clutch applied produces fifth range operation for a limp home capability. If the TCC is
applied, de-energizing the TCC solenoid causes the TCC valve to de-stroke, exhausting pressure
from the top of the converter flow valve. The converter flow valve de-strokes, redirecting main
overage to converter in and converter out to the cooler. The TCC is now released.
If electrical power is interrupted while the transmission is in fourth range (causing fifth range
converter operation) and the manual selector valve is moved to Neutral (N), the 4-5-6 clutch
exhausts through the manual selector valve to exhaust backfill, releasing the 4-5-6 clutch. The
3rd, 5th, and reverse clutch remains applied. With only one clutch applied, the transmission goes
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
to neutral.
If electrical power is interrupted while the transmission is in fourth range (causing fifth range
converter operation) and the manual selector valve is moved to Reverse (R), the 4-5-6 clutch
exhausts through the manual selector valve, releasing the clutch. The 3rd, 5th, and reverse clutch
remains applied. With only one clutch applied, the transmission goes to neutral.
If electrical power is interrupted with the transmission in fourth range, resulting in only fifth
range and neutral operation, the engine may be shut down and restarted to attain neutral, third,
and reverse operation.
Fig. 527: Identifying Hydraulic Circuits Used In Fourth Range
Courtesy of GENERAL MOTORS CORP.
FIFTH RANGE
Before making a shift from fourth to fifth range, the transmission control module (TCM) makes
certain all of the shift valves are in the correct position with shift valve 1 and shift valve 3 stroked
and shift valve 2 de-stroked.
Pressure control solenoid 2 (PCS2) is de-energized, exhausting PCS2 signal pressure and pressure
control valve 2 de-strokes, which allows the 1-2-3-4 clutch to exhaust through the manual selector
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &
Silverado
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