Workshop Repair and Service Manuals GMC SIERRA

Sixth Range Automatic


Before making a shift from fifth to sixth range, thetransmission control module-(TCM) makes certain that allshift valves are in the correct position. Shiftsolenoid-1-(SS1) and SS2 are electrically offand shift valve-1 and shift valve-2 are inthe de-stroked position. SS3 is electrically on and shiftvalve- 3 is in the stroked position.

Pressure control solenoid-1-(PCS1) isenergized, opening PCS1 pressure to exhaust, which allows pressurecontrol valve-3 to de-stroke, exhausting the 3rd, 5th,and reverse clutch pressure and releasing the 3rd, 5th, and reverseclutch. PCS2 is energized, raising the PCS2 signal and PCS2pressure. PCS2 pressure is directed through shiftvalve-1, shift valve-3, shiftvalve-2, and again through shift valve-3 tothe 2-6 clutch, applying the clutch. Main pressure continues toflow through shift valve-3, shift valve-2,and the manual selector valve to the 4-5-6 clutch, keeping the4-5-6 clutch applied. The TCM supplies current to the PCS2, whichcontrols the rate at which the pressure control valve-2supplies pressure to the 2-6 clutch, and current to PCS1, whichcontrols the rate at which the pressure control valve-1exhausts the 3rd, 5th, and reverse clutch, assuring a smoothtransition to sixth range.

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

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

If electrical power is interrupted while the transmission isin sixth range, PCS1 and PCS2, SS3 and the torque converterclutch-(TCC) solenoid (if TCC is applied) arede-energized. Although SS3 supplies control main pressure to thetop of shift valve-3, control main pressure flowsthrough shift valve-1 to the top of shiftvalve-3, keeping the valve in the stroked position.Normally open PCS2 exhausts PCS2 signal pressure, allowing thepressure control valve-2 to de-stroke, exhausting the2-6 clutch. Normally closed PCS1 blocks exhausting of PCS1 signalpressure, allowing PCS1 signal and PCS1 pressure to rise.

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

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

If electrical power is interrupted while the transmission isin 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 toexhaust backfill pressure, releasing the 4-5-6 clutch.

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