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Chevrolet Silverado / GMC Sierra. Manual - part 1176
through the sensor's magnetic field. The AC voltage level and the number of pulses increase as the
speed of the vehicle increases. Output voltage varies with speed from a minimum of 0.5 volts at
100 RPM to more than 100 volts at 8,000 RPM. The TCM converts the pulsing voltage to vehicle
speed. The TCM uses the vehicle speed signal to determine shift timing and torque converter
clutch (TCC) scheduling.
Automatic Transmission Fluid Temperature Sensor
The automatic transmission fluid temperature (TFT) sensor is part of the automatic transmission
fluid pressure (TFP) manual valve position switch. The TFT sensor is a resistor, or thermistor,
which changes value based on temperature. The sensor has a negative-temperature coefficient.
This means that as the temperature increases, the resistance decreases and as the temperature
decreases, the resistance increases.
The transmission control module (TCM) supplies a 5-volt reference signal to the TFT sensor and
measures the voltage drop in the circuit. When the transmission fluid is cold, the sensor resistance
is high and the TCM detects high signal voltage. As the fluid temperature warms to a normal
operating temperature, the resistance becomes less and the signal voltage decreases. Refer to
Transmission Fluid Temperature Sensor Specifications for a complete comparison of sensor
resistance, temperature and signal voltage.
The TCM uses the TFT sensor information to control shift quality and torque converter clutch
(TCC) application.
Transmission Range Switch
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis
Silverado, Sierra & Silverado
Fig. 546: View Of Transmission Range Switch
Courtesy of GENERAL MOTORS CORP.
The transmission range (TR) switch is part of the park/neutral position (PNP) and backup lamp
switch assembly, which is externally mounted on the transmission manual shaft. The TR switch
contains four internal switches that indicate the transmission gear range selector lever position.
The transmission control module (TCM) supplies ignition voltage to each switch circuit. As the
gear range selector lever is moved, the state of each switch may change, causing the circuit to
open or close. An open circuit or switch indicates a high voltage signal. A closed circuit or switch
indicates a low voltage signal. The TCM detects the selected gear range by deciphering the
combination of the voltage signals. The TCM compares the actual voltage combination of the
switch signals to a TR switch combination chart stored in memory.
PARK - ENGINE RUNNING
With the gear selector lever in the PARK (P) position and the engine running, the line pressure
from the oil pump assembly is directed to various components in the valve body and the oil pump.
Pressure Regulator Valve
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis
Silverado, Sierra & Silverado
The pressure regulator valve regulates the oil pump output (line pressure) in response to the signal
fluid pressure, the spring force and the line pressure acting on the end of the valve. The line
pressure is routed through the valve and into both the converter feed and the decrease fluid
circuits. Regulated line pressure is also directed to the manual valve, the converter clutch valve,
the actuator feed limit valve, and the regulated apply valve.
Pressure Relief Valve
Controlled by spring force, this checkball limits the maximum value of the line pressure. When
the line pressure reaches this limiting value, fluid is exhausted past the ball and returns to the
sump.
Line Pressure Tap
The line pressure tap provides a location to measure the line pressure with a fluid pressure gage.
Actuator Feed Limit Valve
Biased by spring force and orificed AFL fluid, it limits the maximum value of line pressure
entering the AFL fluid circuit. Below this limiting value, the AFL fluid pressure equals the line
pressure. The AFL fluid is routed to the pressure control solenoid valve, the 3-2 control solenoid
valve, the TCC PWM solenoid valve, the 1-2 and 2-3 shift solenoid valves, and the 2-3 shift valve
train.
Pressure Control (PC) Solenoid Valve
Controlled by the powertrain control module (PCM), the PC solenoid valve regulates the filtered
AFL fluid into the torque signal fluid pressure. The PCM controls this regulation by varying the
current value to the PC solenoid valve in relation to the throttle position and other vehicle
operating conditions.
Torque Converter Clutch (TCC)
Torque Converter Clutch PWM Solenoid and Regulator Apply and Isolator Valve
AFL fluid is routed to the TCC PWM solenoid valve, in Park the PCM has the duty cycle turned
OFF. This prevents AFL fluid from entering the converter clutch signal fluid circuit. Regulated
line pressure is routed to the regulator apply valve, which is open with CC signal circuit empty,
and blocks line pressure from entering the regulated apply circuit. Any fluid in the regulated
apply circuit will exhaust at the regulated apply valve.
TCC Solenoid Valve
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis
Silverado, Sierra & Silverado
Under normal operating conditions, the PCM keeps the normally open TCC solenoid valve de-
energized (OFF). Converter feed fluid exhausts through the open TCC solenoid valve, and spring
force keeps the converter clutch apply valve in the release position.
Converter Clutch Valve
Held in the release position by spring force, it directs converter feed fluid into the release fluid
circuit. Also, fluid returning from the converter in the apply fluid circuit is routed through the
valve and into the cooler fluid circuit.
Torque Converter
Release fluid pressure unseats the TCC apply checkball (#9), keeps the pressure plate released
from the converter cover and fills the converter with fluid. Fluid exits the converter between the
converter hub and the stator shaft in the apply fluid circuit.
Cooler and Lubrication System
Cooler fluid from the converter clutch apply valve is routed through the transmission fluid cooler
and into the lubrication fluid circuits.
Manual Valve
Controlled by the selector lever and the manual shaft, the manual valve is in the Park (P) position
and directs the line pressure into the PR (Park/Reverse) fluid circuit. Line pressure is blocked
from entering any other fluid circuit at the manual valve.
Lo and Reverse Clutch Applies
Lo and Reverse Clutch Piston
The PR fluid seats the lo and reverse clutch checkball (#10) and is orificed to the outer area of
the piston. Orificing the PR fluid around the #10 checkball helps control the lo and reverse clutch
apply. Also, Lo/reverse fluid pressure from the lo overrun valve acts on the inner area of the lo
and reverse clutch piston in order to increase the clutch holding capacity.
Lo Overrun Valve
IMPORTANT: TCC converter feed valve assembly (#4), in the converter feed
circuit, prevents converter drain down. The orifice is smaller than
the exhaust through the TCC solenoid valve. Therefore, fluid
pressure does not build up at the end of the converter clutch
apply valve.
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis
Silverado, Sierra & Silverado
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