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Code 79, Transmission Fluid Temperature High: Notes

The transmission fluid temperature sensor is a thermistor which controls the signal voltage to the PCM/TCM. The PCM/TCM applies and monitors voltage to the sensor. When transmission fluid is cold, sensor resistance is high; therefore, the PCM/TCM will see high signal voltage. As the transmission fluid warms up, sensor resistance and voltage will drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts.

NOTE: Test numbers refer to numbers on diagnostic chart.
  1. Code 79 will set if signal voltage indicates a transmission fluid temperature greater than 151°C for one second.
  2. This test determines if circuit is shorted to ground, which will result in conditions for Code 79.
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