Code 59, Transmission Temperature Sensor Circuit (Low Temperature Indicated) - LT. Truck: Notes

The transmission temperature sensor is a thermistor which controls signal voltage to PCM/TCM. The PCM/TCM applies and monitors 5 volts to the sensor on circuit No. 1227. When transmission is cold, sensor resistance is high; therefore, the PCM/TCM will see high signal voltage. As transmission temperature warms up, sensor resistance and voltage drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts. See Figure.

1. Code 59 will set if signal voltage indicates a transmission temperature less than -54°F (-48°C) for one second.
2. This test simulates Code 58. If PCM/TCM recognizes the low signal voltage (high temperature) and Scan tester reads 304°F (151°C) or greater, the PCM/TCM 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.