Code 79, Transmission Fluid Temperature High: Notes

Transmission fluid temperature sensor is a thermistor which controls signal voltage to control module. Control module applies and monitors voltage to sensor. When transmission fluid is cold, sensor resistance is high; therefore, control module will see high signal voltage. As transmission fluid warms, 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.

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.