Code 59, Transmission Fluid Temperature Low: Notes
WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1994 GMC Yukon, 1994 GMC Suburban, 1994 GMC Pickup, 1994 GMC Cab & Chassis, and 1994 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.
The transmission fluid temperature sensor is a thermistor which controls the signal voltage to PCM/TCM. The PCM/TCM applies and monitors 5 volts to the sensor. When transmission fluid is cold, sensor resistance is high; therefore, the PCM/TCM will see high signal voltage. As transmission fluid 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.
NOTE:
Test numbers refer to numbers on diagnostic chart.
- Code 59 will set if signal voltage indicates a transmission fluid temperature less than -34°F (-37°C) for one second.
- This test simulates Code 58. If PCM/TCM recognizes low signal voltage (high temperature) and scan tester reads 305°F (151°C) or greater, PCM/TCM and wiring are okay.
- This test determines if signal circuit is open. There should be 5 volts present at the sensor connector if measuring with a DVOM.