F.
Hydraulic Circuit—Fourth Range (Foldout 8) • Before making the shift from third to fourth range, the TCM makes certain all of the shift valves are in the correct position, with SV1 stroked and SV2 and SV3 de-stroked. • PCS1 is energized, opening the PCS1 signal pressure to exhaust which allows the PCV1 to de-stroke and C3 clutch pressure is exhausted. PCS2 is energized, raising the PCS2 signal and PCS2 pressures. The PCS2 pressure is directed through SV1, SV3, SV2 and the Manual Selector Valve to C2 clutch, applying the clutch. Main pressure continues to flow through SV3 and the Manual Selector Valve to C1 clutch, keeping C1 clutch applied. The TCM supplies current to PCS2, which controls the rate at which PCV2 supplies pressure to C2 clutch, and current to PCS1, which controls the rate at which PCV1 exhausts C3 clutch, assuring a smooth transition to fourth range. • The combination of C1 and C2 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 SV3, stroking the valve. In its stroked position, main pressure is redirected through SV2 and the Manual Selector Valve to C2 clutch, keeping C2 clutch applied. The flow from PCV2 to SV3 is directed through the Manual Selector Valve to C1 clutch, keeping C1 clutch applied. • PS3 turns on and PS1 remains on, providing feedback that the valves are stroked. PS2 remains off, providing feedback that SV2 is in its de-stroked position. • If electrical power is interrupted while the transmission is in fourth range, PCS1, PCS2, and TCC solenoids, and SS1 and SS3 are deenergized. Main pressure continues to flow
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Copyright © 2005 General Motors Corp.
through SV3 and SV2 and the Manual Selector Valve to C2 clutch, keeping C2 clutch applied. When de-energized, normally open PCS2 exhausts the PCS2 signal pressure, allowing PCV2 to de-stroke and C1 clutch exhausts. After SV1 de-strokes, the C1 clutch exhausts to exhaust backfill. Normally closed PCS1 blocks the exhaust of PCS1 signal pressure, allowing the PCS1 signal and PCS1 pressures to rise. PCV1 directs full pressure through SV2 to C3 clutch, applying the clutch. The combination of C2 and C3 clutches 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, C2 clutch exhausts through the Manual Selector Valve to exhaust backfill, releasing C2 clutch. C3 clutch remains applied. With only one clutch applied, the transmission goes 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, C2 clutch exhausts through the Manual Selector Valve, releasing the clutch. C3 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 (refer to paragraph A—Neutral).
1000 and 2000 Product Families Principles of Operation—May 2005
