Transaxle Fluid Temperature (TFT) Sensor

Fig 1: Cut-Away View Of Shift Solenoid

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The TFT sensor is a positive temperature coefficient thermistor (temperature sensitive resistor) that provides information to the TCM regarding transaxle fluid temperature. The temperature sensor is located in valve body. Calculated temperature is a factor used to determine the shift time and shift delay time.

The internal electrical resistance of the sensor varies in relation to the operating temperature of the transaxle fluid (see chart).

Fig 2: Transaxle Fluid Temperature Sensor Temperature/Resistance Chart

Courtesy of SUZUKI OF AMERICA CORP.

The TCM sends a 5 volt-reference signal to the temperature sensor and measures the voltage rise in the electrical circuit. A higher fluid temperature creates a higher resistance in the temperature sensor, thereby measuring a lower voltage signal.

Fig 3: Identifying Transaxle Fluid Temperature Sensor

Courtesy of SUZUKI OF AMERICA CORP.

The TCM measures this voltage as another input to help control line pressure, shift schedules and TCC apply.

When transaxle fluid temperature reaches 140 °C (284 °F) the TCM enters "hot mode." Above this temperature the TCM modifies transaxle shift schedules and TCC apply in an attempt to reduce fluid temperature by reducing transaxle heat generation. During hot mode the TCM applies the TCC at all times in fourth gear.

Also, the TCM commands the 2-3 and 3-4 shifts earlier to help reduce fluid heat generation. Hot mode may not be available on some applications.

Fig 4: Transaxle Sensor - Temperature-To-Resistance-To-Voltage Chart

Courtesy of SUZUKI OF AMERICA CORP.