Chevrolet Silverado / GMC Sierra. Service manual — part 816

Fig. 210: Drive Range, Second Gear
Courtesy of GENERAL MOTORS CORP.

DRIVE RANGE, THIRD 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 OFF the normally-low CB26
pressure control solenoid 4. At the same time the C35R pressure control solenoid 2 is also
commanded ON to regulate 3-5 clutch apply.

3-5 REVERSE CLUTCH APPLIES

C35R Pressure Control Solenoid 2

The C35R pressure control solenoid 2 is commanded 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 35 reverse clutch fluid pressure acts on a differential area moving the 3-5 reverse clutch
boost valve against the 3-5 reverse clutch boost valve spring. The 35 reverse clutch fluid passes
through the valve and enters the 35 reverse clutch feedback circuit. As PCS 35 reverse clutch
fluid pressure is increased to a given value, the 3-5 reverse clutch boost valve opens the 35
reverse clutch feedback circuit to exhaust. This results in the 3-5 reverse clutch regulator valve
moving to the full feed position sending full 35 reverse clutch feed pressure (full line pressure) to
the clutch.

3-5 Reverse Clutch Regulator Valve

PCS 35 reverse clutch fluid moves the 3-5 reverse clutch regulator valve against 3-5 reverse
clutch regulator valve spring force and 35 reverse clutch feedback fluid. This allows 35 reverse
feed to pass through the valve and enter the 35 reverse clutch circuit. The 35 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 35 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.

2-6 CLUTCH RELEASES

CB26 Pressure Control Solenoid 4

The CB26 pressure control solenoid 4 is commanded OFF allowing PCS 26 clutch fluid from the
2-6 clutch regulator valve to exhaust. The 26 clutch/1234 clutch feed fluid at the 2-6 clutch
regulator valve passes through the valve and enters the PS3 fluid circuit. PS3 fluid is then routed
to pressure switch 3 and opens the normally-closed switch.

2-6 Clutch Regulator Valve

The 2-6 clutch regulator valve spring force moves the valve to allow 26 clutch fluid from the 2-6
clutch to pass through the valve and enter the exhaust backfill fluid circuit.

2-6 Clutch

The 2-6 clutch spring force moves the 2-6 clutch piston to release the 2-6 clutch plates and forces
26 clutch fluid to exhaust from the center support. The 26 clutch fluid is routed through the 2-6
clutch regulator valve where it enters the exhaust backfill fluid circuit and is routed through
orifice #30 to the exhaust backfill pressure relief valve where excess pressure is exhausted.

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

Fig. 211: Drive Range, Third Gear
Courtesy of GENERAL MOTORS CORP.

DRIVE RANGE, THIRD GEAR DEFAULT

If the transmission is in 1st, 2nd or 3rd gear during a transmission electrical component failure,
the transmission will default to 3rd gear. All solenoids will default to their normal state. If the
torque converter clutch was applied, it will release. This default action will enable the vehicle to
be safely driven to a service center.

1-2-3-4 CLUTCH STAYS APPLIED

Shift Solenoid 2

Shift solenoid 2 defaults to it's normally-closed state (OFF), and SOL 2 fluid exhausts through the
solenoid.

Clutch Select Valve 3

Solenoid 2 fluid pressure no longer holds the clutch select valve 3 open. When the valve moves
back to the closed position, it opens the 1234 clutch default fluid circuit, and 1234 default fluid is
routed to the 1-2-3-4 clutch regulator valve.

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

1-2-3-4 Clutch Regulator Valve

With the absence of PCS 1234 clutch fluid, due to the default state of the C1234 pressure control
solenoid 5, the 1-2-3-4 regulator valve would close from spring force. However, the 1234 clutch
default fluid enters behind the 1-2-3-4 regulator shuttle valve and keeps the valve in the open
position.

1-2-3-4 Clutch

With the 1-2-3-4 clutch regulator valve still held in the open position, the 1-2-3-4 clutch will stay
applied.

3-5 REVERSE CLUTCH APPLIED OR APPLIES

C35R Pressure Control Solenoid 2

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

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. 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 Boost Valve

PCS 3-5 reverse clutch fluid pressure acts on a differential area moving the 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

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

2008 Chevrolet Silverado 1500

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

Sierra & Silverado