Transmission Temperature Sensor/Switch: Description and Operation

TEMPERATURE SENSORS
The Hydra-matic 4T60-E transmission uses two styles of temperature sensors. One sensor is screwed into the channel plate near the TCC accumulator bore. This sensor monitors the fluid temperatures in the cooler circuit.
The other style sensor is incorporated into the wiring harness and clips to the valve body spacer plate. This type of sensor monitors the transmission fluid temperatures in the side cover.

SENSOR FUNCTION AND TCC OPERATION
Both sensors are negative temperature coefficient thermistors that provide transmission fluid temperature information to the PCM. The PCM sends a 5-volt reference signal to the sensors and measures the voltage drop in the circuit. The internal resistance of the sensors changes as the operating temperature of the transmission fluid changes. The PCM then uses this information to determine when to engage or disengage the TCC.
The PCM inhibits TCC operation until the transmission fluid temperature reaches approximately 45°C (113°F). At this temperature the PCM allows the TCC to engage, if the throttle position, gear range and other vehicle operating conditions are appropriate.

HOT MODE OPERATION
Transmission fluid temperatures may become excessively high, above approximately 130°C (266°F). When this happens, the PCM modifies its shift pattern and its TCC schedules in order to reduce the heat generated by fluid coupling in the torque converter. These events occur during hot mode operation when the PCM commands the transmission into the lower gear ranges (3rd or 2nd gear) and applies the TCC.
If a situation occurs where a short or open is detected in the circuit, the PCM uses a default value for transmission temperature.