Chevrolet Silverado / GMC Sierra. Service manual — part 818

plates.

1-2-3-4 CLUTCH RELEASES

C1234 Pressure Control Solenoid 5

The C1234 pressure control solenoid 5 is commanded OFF, allowing PCS 1234 clutch fluid from
the 1-2-3-4 clutch regulator valve and 1-2-3-4 clutch boost valve to exhaust.

1-2-3-4 Clutch Regulator Valve

The 1-2-3-4 clutch regulator valve spring force moves the valve to allow 1234 clutch feed fluid
from the 1-2-3-4 clutch to pass through the valve and enter the exhaust backfill fluid circuit. The
1234 clutch fluid the enters the exhaust backfill fluid circuit and is routed through orifice #30 to
the exhaust backfill pressure relief valve where excess pressure is exhausted. Also, 1234 clutch
regulator valve spring force moves the valve to allow 1234 clutch feed fluid to pass through the
valve and enter the PS4 fluid circuit. PS4 fluid is then routed to pressure switch 4 and opens the
normally-closed switch.

1-2-3-4 Clutch Boost Valve

The 1-2-3-4 clutch boost valve spring force moves the valve to allow 1234 clutch feedback fluid
from the 1-2-3-4 clutch regulator valve to enter the 1234 clutch circuit and exhaust.

1-2-3-4 Clutch

The 1-2-3-4 clutch spring force combined with force from the compensator moves the 1-2-3-4
clutch piston to release the clutch plates and force 1234 clutch fluid from the 1-2-3-4 and 3-5
reverse clutch housing. The 1234 clutch fluid is routed through the 1-2-3-4 clutch regulator valve
where it enters the exhaust backfill fluid circuit.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Fig. 214: Drive Range, Fifth Gear
Courtesy of GENERAL MOTORS CORP.

DRIVE RANGE, FIFTH GEAR DEFAULT

If the transmission is in 4th, 5th or 6th gear during a transmission electrical component failure, the
transmission will default to 5th gear. All solenoids will default to their normal state. If the torque
converter clutch was applied, it will release. The transmission will stay in 5th gear default range
until the ignition has been turned off or transmission shifted to reverse. When the vehicle is
restarted, and shifted back into drive, the transmission will then operate in the 3rd gear default
range. This default action will enable the vehicle to be safely driven to a service center.

3-5 REVERSE CLUTCH APPLIES

C35R Pressure Control Solenoid 2

The C35R pressure control solenoid 2 defaults to ON, allowing actuator feed fluid to enter the
pressure control solenoid (PCS) 35 reverse clutch fluid circuit. PCS 35 reverse clutch fluid is
routed through orifice #48 and then to the 3-5 reverse clutch regulator valve. PCS 35 reverse
clutch fluid is also routed through orifice #40 and then to the 3-5 reverse clutch boost valve.

3-5 Reverse Clutch Boost Valve

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

PCS 3-5 reverse clutch fluid pressure acts on a differential area moving the PCS 3-5 reverse
clutch boost valve against the 3-5 reverse clutch boost valve spring. The 3-5 reverse clutch fluid
passes through the valve and enters the 3-5 reverse clutch feedback circuit. As PCS 3-5 reverse
clutch fluid pressure is increased to a given value, the 3-5 reverse clutch boost valve opens the 3-5
reverse clutch feedback circuit to exhaust. This results in the 3-5 reverse clutch regulator valve
moving to the full feed position sending full 3-5 reverse clutch feed pressure (full line pressure) to
the clutch.

3-5 Reverse Clutch Regulator Valve

PCS 3-5 reverse clutch fluid moves the 3-5 reverse clutch regulator valve against 3-5 reverse
clutch regulator valve spring force and 3-5 reverse clutch feedback fluid. This allows 3-5 reverse
feed to pass through the valve and enter the 3-5 reverse clutch circuit. The 3-5 reverse clutch fluid
is then routed to the 3-5 reverse clutch, the 3-5 reverse boost valve and the clutch select valve 2.
When the 3-5 reverse clutch regulator valve is in this position, PS1 fluid from the pressure switch
1 exhausts through the valve, allowing the switch to close.

3-5 Reverse Clutch

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

Clutch Select Valve 3

Once the clutch select valve 3 is moved to the ON position in 4th gear, it will remain in this
position throughout the 5th gear default range, until the ignition has been turned OFF. When the
ignition is OFF, fluid will exhaust from the valve, thus when the vehicle is restarted, the
transmission will then be in the 3rd gear default range.

1-2-3-4 CLUTCH RELEASES OR 2-6 CLUTCH RELEASES

C1234 Pressure Control Solenoid 5

If the transmission was in 4th gear when an electrical condition commands a protection mode, the
C1234 pressure control solenoid 5 defaults to the OFF position, allowing PCS 1234 clutch fluid
from the 1-2-3-4 clutch, the 1-2-3-4 clutch regulator valve and 1- 2-3-4 clutch boost valve to
exhaust.

2-6 CB26 Pressure Control Solenoid 4

If the transmission was in 6th gear when an electrical condition commands a protection mode, the
CB26 pressure control solenoid 4 defaults to the OFF position, allowing PCS 26 clutch fluid

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

from the 2-6 clutch regulator valve, and the 2-6 clutch to exhaust.

TORQUE CONVERTER CLUTCH RELEASES

TCC Pressure Control Solenoid

The torque converter clutch (TCC) pressure control solenoid will default to it's normal state,
OFF. PCS TCC fluid will exhaust from the TCC control valve, and spring force will shuttle the
valve to the off position. TCC apply fluid will then be routed to the cooler, and TCC release fluid
will be routed to the torque converter for complete TCC release.

Fig. 215: Drive Range, Fifth Gear Default
Courtesy of GENERAL MOTORS CORP.

DRIVE RANGE, SIXTH GEAR

As the vehicle speed increases, the transmission control module (TCM) receives input signals
from the automatic transmission input and output speed sensors, the throttle position sensor and
other vehicle sensors to determine the precise moment to command ON the normally-low CB26
pressure control solenoid 4 (PCS). At the same time the normally-high C35R pressure control
solenoid 2 is commanded OFF.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado