Workshop Repair and Service Manuals GMC SIERRA
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Drive Range Third Gear Default Automatic

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If the transmission is in 1st, 2nd or 3rd gear during atransmission electrical component failure, the transmission willdefault to 3rd-gear. All solenoids will default to theirnormal state. If the torque converter clutch was applied, it willrelease. This default action will enable the vehicle to be safelydriven to a service center.

1-2-3-4 Clutch Stays Applied

Shift Solenoid 2

Shift solenoid-2 defaults to it'snormally-closed state (OFF), and SOL-2 fluidexhausts through the solenoid.

Clutch Select Valve 3

Solenoid-2 fluid pressure no longer holds theclutch select valve-3 open. When the valve moves back tothe closed position, it opens the 1234-clutch defaultfluid circuit, and 1234-default fluid is routed to the1-2-3-4-clutch regulator valve.

1-2-3-4 Clutch Regulator Valve

With the absence of PCS-1234 clutch fluid, due tothe default state of the C1234-pressure controlsolenoid-5, the 1-2-3-4-regulator valve wouldclose from spring force. However, the 1234-clutchdefault fluid enters behind the 1-2-3-4-regulatorshuttle valve and keeps the valve in the open position.

1-2-3-4 Clutch

With the 1-2-3-4-clutch regulator valve still heldin the open position, the 1-2-3-4-clutch will stayapplied.

3-5 Reverse Clutch Applied or Applies

C35R Pressure Control Solenoid 2

The normal state for the C35R-pressure controlsolenoid-2 is ON, therefore PSC-35 reverseclutch fluid will still be routed to the 3-5-reverseclutch regulator valve and the 3-5-reverse clutch boostvalve.

3-5 Reverse Clutch Regulator Valve

PCS-3-5 reverse clutch fluid moves the3-5-reverse clutch regulator valve against3-5-reverse clutch regulator valve spring force and3-5-reverse clutch feedback fluid. This allows3-5-reverse feed to pass through the valve and enter the3-5-reverse clutch circuit. 3-5-reverseclutch fluid is then routed to the 3-5-reverse clutch,the 3-5-reverse boost valve and the clutch selectvalve-2. When the 3-5-reverse clutchregulator valve is in this position, PS1-fluid from thepressure switch-1 exhausts through the valve, allowingthe switch to close.

3-5 Reverse Clutch Boost Valve

PCS-3-5 reverse clutch fluid pressure acts on adifferential area moving the 3-5-reverse clutch boostvalve against the 3-5-reverse clutch boost valve spring.The 3-5-reverse clutch fluid passes through the valveand enters the 3-5-reverse clutch feedback circuit. AsPCS-3-5 reverse clutch fluid pressure is increased to agiven value, the 3-5-reverse clutch boost valve opensthe 3-5-reverse clutch feedback circuit to exhaust. Thisresults in the 3-5-reverse clutch regulator valve movingto the full feed position sending full 3-5-reverseclutch feed pressure (full line pressure) to the clutch.

3-5 Reverse Clutch

The 3-5-reverse clutch fluid enters the 1-2-3-4and 3-5-reverse clutch housing to move the pistonagainst spring force combined with force from the compensator toapply the 3-5-reverse clutch plates.

Drive Range, Third Gear Default

Drive Range, Third Gear Default Automatic

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