Fluid Pressure Sensor/Switch: Description and Operation
Automatic Transmission Pressure Control Solenoid Valve
4T40-E/4T45-E
The Pressure Control (PC) solenoid valve is a precision electronic pressure regulator that controls the transmission line pressure. This control is based on the flow of current through the valve's coil windings. As the flow of current is increased, the magnetic field which is produced by the coil moves the solenoid's plunger further away from the exhaust port. Opening the exhaust port decreases the output fluid pressure regulated by the PC solenoid valve, which ultimately decreases line pressure.
The Powertrain Control Module (PCM) controls the PC solenoid valve based on various inputs, including throttle position, fluid temperature, MAP sensor, and gear state.
The PCM controls the PC solenoid valve on a positive duty cycle at a fixed frequency of 614 Hz. Duty cycle is defined as the percent of time current is flowing through the solenoid coil during each cycle. A higher duty cycle provides a greater current flow through the solenoid.
The high (positive) side of the PC solenoid valve electrical circuit at the PCM controls the PC solenoid valve operation. The PCM provides a ground path for the circuit, monitors average current and continuously varies the PC solenoid valve duty cycle to maintain the correct average current flowing through the PC solenoid valve.
The resistance on the PC solenoid valve should measure between 3-5 ohms at 20° C (68° F).
Automatic Transmission Fluid Pressure Manual Valve Position Switch Assemble
4T40-E/4T45-E
The automatic Transmission Fluid Pressure (TFP) manual valve position switch assembly is attached to the control valve body. This assembly contains six fluid pressure switches and the automatic transmission fluid temperature sensor.
Five of the fluid pressure switches are normally-open. These are used to indicate the position of the manual valve. The Powertrain Control Module (PCM) uses this information to control line pressure, Torque Converter Clutch (TCC) apply and release and shift solenoid operation.
The release pressure switch is used as a diagnostic tool to confirm that the TCC is actually OFF when it has been commanded OFF by the PCM. This switch is normally-closed.
Each fluid pressure switch produces either an open or a ground to the PCM depending on the presence of fluid pressure at the switches. The sequence of open and closed switches produces a combination of voltage readings. The PCM monitors these readings.
The PCM measures Transmission Fluid Pressure (TFP) manual valve position switch signal voltage from each pin to ground and compares the voltage to a TFP manual valve position switch combination table stored in the PCM memory. If the PCM does not recognize the switch sequence, a diagnostic code will be set as a result. A diagnostic code may also set if the TFP manual valve position switch sequence indicates a gear range selection that conflicts with other sensory inputs to the PCM.
Fluid Pressure and Circuit Combination
4T40-E/4T45-E
Valid combinations for Circuits A, B. and C are shown in the table. On means that the switch is grounded with a resistance less than 50 ohms at 0 volts OFF means that the switch is open with a resistance greater than 50 K ohms at 12 volts.
Note that resistance should be measured with the engine running. When the transmission's pass through connector is disconnected from the vehicle harness while the engine is running, multiple diagnostic codes will set. Clear these codes when you are finished with this procedure.