GM Service Manual Online
For 1990-2009 cars only

Before making a shift from fifth to sixth range, the transmission control module (TCM) makes certain that all shift valves are in the correct position. Shift solenoid 1 (SS1) and SS2 are electrically off and shift valve 1 and shift valve 2 are in the de-stroked position. SS3 is electrically on and shift valve  3 is in the stroked position.

Pressure control solenoid 1 (PCS1) is energized, opening PCS1 pressure to exhaust, which allows pressure control valve 3 to de-stroke, exhausting the 3rd, 5th, and reverse clutch pressure and releasing the 3rd, 5th, and reverse clutch. PCS2 is energized, raising the PCS2 signal and PCS2 pressure. PCS2 pressure is directed through shift valve 1, shift valve 3, shift valve 2, and again through shift valve 3 to the 2-6 clutch, applying the clutch. Main pressure continues to flow through shift valve 3, shift valve 2, and the manual selector valve to the 4-5-6 clutch, keeping the 4-5-6 clutch applied. The TCM supplies current to the PCS2, which controls the rate at which the pressure control valve 2 supplies pressure to the 2-6 clutch, and current to PCS1, which controls the rate at which the pressure control valve 1 exhausts the 3rd, 5th, and reverse clutch, assuring a smooth transition to sixth range.

The combined application of the 4-5-6 clutch and the 2-6 clutch produces sixth range operation.

Pressure switch 1 and pressure switch 2 remain open (OFF) providing feedback that shift valve 1 and shift valve 2 remain in the de-stroked position, and pressure switch 3 remains closed (ON) providing feedback that shift valve 3 remains in the stroked position.

If electrical power is interrupted while the transmission is in sixth range, PCS1 and PCS2, SS3 and the torque converter clutch (TCC) solenoid (if TCC is applied) are de-energized. Although SS3 supplies control main pressure to the top of shift valve 3, control main pressure flows through shift valve 1 to the top of shift valve 3, keeping the valve in the stroked position. Normally open PCS2 exhausts PCS2 signal pressure, allowing the pressure control valve 2 to de-stroke, exhausting the 2-6 clutch. Normally closed PCS1 blocks exhausting of PCS1 signal pressure, allowing PCS1 signal and PCS1 pressure to rise.

PCS1 pressure is directed through shift valve 2 to the 3rd, 5th, and reverse clutch, applying the clutch. Main pressure continues to flow through shift valve 3, shift valve 2, and the manual selector valve to the 4-5-6 clutch, keeping the 4-5-6 clutch applied. The combination of 4-5-6 clutch and 3rd, 5th, and reverse clutch application produces fifth range operation for limp home capability.

If the TCC is applied, the TCC solenoid de-energizes, causing the TCC valve to de-stroke, exhausting pressure form the top of the converter flow valve. De-stroking the converter flow valve redirects main overage pressure to "converter in" path, then to "converter out" proceeding on to the transmission oil cooler. The TCC is now released.

If electrical power is interrupted while the transmission is in sixth range (causing sixth range converter operation [TCC OFF]) and the manual selector valve is moved to Neutral (N), the 4-5-6 clutch exhausts through the manual selector valve to exhaust backfill pressure, releasing the 4-5-6 clutch. The 3rd, 5th, and reverse clutch remains applied. With only one clutch applied the transmission shifts to neutral

If electrical power is interrupted while the transmission is in sixth range (causing fifth range converter operation [TCC OFF]) and the manual selector valve is moved to Reverse (R), the 4-5-6 clutch exhausts through the manual selector valve to exhaust backfill pressure, releasing the 4-5-6 clutch. The 3rd, 5th, and reverse clutch remains applied. With only one clutch applied, the transmission shifts to neutral.

If electrical power is interrupted while the transmission is in sixth range, resulting in only fifth range and neutral operation, the engine may be shut down and restarted to attain neutral, drive, and reverse operation.

Sixth Range


Object Number: 1660887  Size: FS