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