K 2500 Truck 4WD V8-6.5L DSL Turbo VIN S (1998)
Shift Solenoid: Description and Operation
4L80-E Automatic Transmission
TRANSMISSION PRESSURE CONTROL SOLENOID VALVE (FORCE MOTOR)
The pressure control (PC) solenoid valve is attached to the valve body. The valve controls line pressure by moving a pressure regulator valve against
spring pressure. The PC solenoid valve takes the place of the throttle valve or the vacuum modulator, which was used on past model transmissions.
The VCM/PCM varies line pressure based on engine load. Engine load is calculated from various inputs, especially the TP sensor switch. Line
pressure is actually varied by changing the amperage applied to the PC solenoid valve from 0 amps (high pressure) to 1.1 amps (low pressure).
One diagnostic code is associated with the PC solenoid valve. Code P0748 sets when the VCM/PCM detects a difference of .16 amp or more between
the amperage commanded and actual amperage. While the code is set, the PC solenoid valve turns OFF. Recovery can occur after the next ignition
cycle. Code P0748 does not sense a hydraulic problem such as a stuck valve.
1-2 SHIFT SOLENOID VALVE
The 1-2 Shift Solenoid valve is attached to the valve body and is a normally open exhaust valve. The VCM/PCM activates the solenoid by grounding
the solenoid through an internal quad driver. The 1-2 Shift Solenoid valve is ON in First and Fourth gear, but OFF in Second and Third gears. When
ON, the valve redirects fluid to act on the shift valve. The 1-2 Shift Solenoid valve is usually black in color.
Two diagnostic codes are associated with the 1-2 Shift Solenoid valve: P0753 and P0751.
The first code is Code P0753 (1-2 Shift Solenoid Valve-electrical). The VCM/PCM continually monitors the 1-2 Shift Solenoid circuit for expected
voltage. If the voltage reading is not what is expected, Code P0753 will be set. While Code P0753 is present, the VCM/PCM will default to maximum
line pressure, freeze shift adapts from being updated and the MIL will not illuminate. Recovery can occur on the next ignition cycle.
Code P0751 (1-2 Shift Solenoid Valve-Performance) is set when the VCM/PCM detects First or Second gear at high speed. The VCM/PCM default
action is Second gear only.
