Chevrolet Silverado / GMC Sierra. Service manual — part 1183

fluid pressure switch. The combination of the opened D3 switch and the closed D4 switch signals
the PCM that the transmission is operating in Manual Third.

1-2 Shift Solenoid (SS) Valve

When Manual Third is selected, the PCM de-energizes the 1-2 SS valve to immediately downshift
the transmission into Third gear. This electronically prevents Fourth gear.

3-4 Shift Valve

D3 fluid pressure assists spring force to keep the valve in the downshifted position against the
signal A fluid circuit. In this position, the valve blocks 3-4 signal fluid and the 4th signal fluid
circuit is open to an exhaust port past the valve. Therefore, with D3 fluid pressure assisting spring
force, Fourth gear is hydraulically prevented.

2-3 Shift Valve Train

With the 2-3 SS valve de-energized and open, actuator feed limit (AFL) fluid acting on the 2-3
shift valve holds both valves in the upshifted position. This allows D3 fluid to feed the overrun
fluid circuit through the 2-3 shift valve.

Overrun Clutch Feed Checkball (#5)

Overrun fluid pressure seats the ball against the empty D2 fluid circuit.

Overrun Clutch Control Checkball (#6)

Overrun fluid pressure seats the #6 checkball and is orificed (#20) to fill the overrun clutch feed
fluid circuit. This orifice controls the overrun clutch apply rate.

3-4 Relay Valve and 4-3 Sequence Valve

4th signal fluid pressure is exhausted from the end of the 3-4 relay valve. Overrun clutch feed
fluid pressure assists spring force and closes both valves. This allows overrun clutch feed fluid to
flow through the 4-3 sequence valve and fill the overrun clutch fluid circuit.

Overrun Clutch Piston

Overrun clutch fluid pressure moves the piston to apply the overrun clutch plates. The overrun
clutch plates provide engine compression braking in Manual Third - Third Gear.

Overrun Clutch Air Bleed Checkball

This ball and capsule is located in the overrun clutch fluid circuit in the oil pump. It allows air to

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

exhaust from the circuit as fluid pressure increases and also allows air into the circuit to displace
the fluid when the clutch releases.

Torque Converter Clutch and Torque Converter Clutch PWM Solenoid Valve

The PCM de-energizes the TCC solenoid valve and operates the duty cycle of the TCC PWM
solenoid valve to release the converter clutch prior to downshifting, (assuming the converter
clutch is applied in Overdrive Range-Fourth Gear when Manual Third is selected). The PCM will
re-apply the converter clutch in Manual Third-Third Gear when proper driving conditions have
been met.

Pressure Control (PC) Solenoid Valve

The PC solenoid valve operates in the same manner as Overdrive Range, regulating in response to
throttle position and other vehicle operating conditions.

Manual Third - First and Second Gears: Overrun Clutch Released

In Manual Third, the transmission upshifts and downshifts normally between First, Second and
Third gears. However, in First and Second gears, the 2-3 SS valve is energized and the 2-3 shift
valve train is in the downshifted position. The 2-3 shift valve blocks D3 fluid from entering the
overrun fluid circuit and opens the overrun fluid circuit to an exhaust port at the valve. This
prevents overrun clutch apply and engine compression braking in Manual Third-First and Second
Gears.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

Fig. 556: Manual Third Gear
Courtesy of GENERAL MOTORS CORP.

MANUAL SECOND GEAR

A manual 3-2 downshift can be accomplished by moving the gear selector lever into the Manual
Second (2) position when the transmission is operating in third gear. This causes the transmission
to shift immediately into second gear regardless of vehicle operating conditions. Also, the
transmission is prevented from operating in any other gear, first, third or fourth. The following
information explains the additional changes during a manual 3-2 downshift, as compared to a
forced 3-2 downshift. Some vehicles in manual second gear will start out in first gear, while other
vehicles will have a second gear start. Refer to the owners manual for specific applications.

Manual Valve

The selector lever moves the manual shaft and the manual valve into the manual second (2)
position. This allows the line pressure to enter the D2 fluid circuit.

Transmission Fluid Pressure (TFP) Manual Valve Position Switch Assembly

The D2 fluid is routed to the TFP manual valve position switch where it opens the normally
closed D2 fluid pressure switch. With the D2 and the D3 pressure switches closed and the D4

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

pressure switch open, the TFP manual valve position switch signals the PCM that the transmission
is operating in manual second.

Third and Fourth Gears Prevented

2-3 Shift Solenoid (SS) Valve

The PCM energizes the 2-3 SS valve and the AFL fluid pressure holds the 2-3 shift valve in the
downshift position. This electronically prevents operation of the third and fourth gears.

2-3 Shift Valve Train

The D2 fluid is routed between the 2-3 shuttle and the 2-3 shift valves and causes the following:

Regardless of the operating conditions, the D2 fluid pressure holds the 2-3 shift valve in the
downshift position against the AFL fluid pressure.

The 2nd fluid is blocked from entering the 3-4 signal fluid circuit and the 3-4 signal fluid
circuit is open to an exhaust port at the valve.

The 3-4 clutch cannot apply with the 3-4 signal fluid exhausted. Therefore, third and fourth
gears are hydraulically prevented.

The 2nd fluid feeds the servo feed fluid circuit, but the 2nd fluid circuit has no function in
manual second.

The AFL fluid is blocked by the 2-3 shift valve and the D432 fluid circuit is exhausted
through the valve.

The overrun fluid is exhausted through the 2-3 shuttle valve.

1-2 Shift Valve

The 1-2 SS valve is OFF, the signal A fluid exhausts through the solenoid and the spring force
holds the valve in the upshifted position.

First Gear Prevented

The prevention of first gear is controlled electronically by the PCM through the 1-2 SS valve.
The PCM keeps the 1-2 SS valve de-energized, regardless of the vehicle operating conditions
when the TFP manual valve position switch signals manual second gear range. This keeps signal
A fluid exhausted and the spring force holds the 1-2 shift valve in the upshift position.

Overrun Clutch Remains Applied

Overrun Clutch Feed Checkball (#5)

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado