Code 59, Transmission Fluid Temp. Sensor Circuit (Low Temp. Indicated): Notes

The transmission fluid temperature sensor, located within the fluid pressure switch assembly, is a thermistor which controls the signal voltage to the PCM. The PCM applies and monitors 5 volts to the sensor on circuit No. 1227. When transmission fluid is cold, sensor resistance is high; therefore, the PCM will see high signal voltage. As the 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. When Code 59 is set, transmission will use a warm value for operation, but scan tester will display the actual fluid temperature.

1. Code 59 will set if signal voltage indicates a transmission fluid temperature less than -27°F (-33°C) for one second.
2. This test simulates Code 58. If PCM recognizes the low signal voltage (high temperature) and scan tester reads 309°F (154°C) or greater, the PCM and wiring are okay.
3. This test determines if circuit No. 1227 is open. There should be 5 volts present at the sensor connector if measuring with a DVOM.