4T40-E Automatic Transaxle

AUTOMATIC TRANSMISSION FLUID PRESSURE
MANUAL VALVE POSITION SWITCH ASSEMBLY





The Automatic Transmission Fluid Pressure Manual Valve Position Switch (TFP 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 PCM uses this information to control line pressure, 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 TFP Valve Position Switch signal voltage from each pin to ground and compares the voltage to a TFP 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 Valve Position Switch sequence indicates a gear range selection that conflicts with other sensory inputs to the PCM.

FLUID PRESSURE AND CIRCUIT COMBINATION





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.


AUTOMATIC TRANSMISSION FLUID TEMPERATURE SENSOR





The Automatic Transmission Fluid Temperature (TFT) sensor is a negative temperature coefficient thermistor that provides information to the PCM regarding transmission fluid temperature. The temperature sensor is integrated in the Automatic Transmission Fluid Pressure Manual Valve Position Switch (TFP Valve Position Switch) Assembly which is bolted to the control valve body. The sensor monitors main line pressure from the inside of the control valve body, in order to determine the operating temperature of the transmission fluid. The sensor uses an O-ring seal to maintain fluid pressure in the control valve body.
The internal electrical resistance of the sensor varies in relation to the operating temperature of the transmission fluid. The PCM sends a 5-volt reference signal to the temperature sensor. This measures the voltage drop in the electrical circuit. A lower fluid temperature creates a higher resistance in the temperature sensor, thereby measuring a higher voltage signal.
The PCM measures this voltage as another input to help control line pressure, shift schedules and TCC apply. When the TFT reaches 140°C (284°F), the PCM enters hot mode. Above this temperature the PCM modifies the transmission shift schedules and TCC apply in an attempt to reduce fluid temperature by reducing the amount of heat generated by the transmission. During hot mode the PCM applies TCC at all times in Third and Fourth gears. Also, the PCM performs the 2-3 and the 3-4 shifts earlier in order to help reduce the generation of fluid heat.





TRANSMISSION SENSOR - TEMPERATURE TO RESISTANCE TO VOLTAGE (APPROXIMATE)