CODE 59, TRANSMISSION FLUID TEMPERATURE LOW GMC Suburban I

CODE 59, TRANSMISSION FLUID TEMPERATURE LOW

Transmission fluid temperature sensor is a thermistor which controls signal voltage to control module. Control module applies and monitors 5 volts to sensor. When transmission fluid is cold, sensor resistance is high; therefore, control module will see high signal voltage. As transmission fluid temperature warms, 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.

1. Code 59 will set if signal voltage indicates a transmission fluid temperature less than -34°F (-37°C) for one second.
2. This test simulates Code 58. If control module recognizes low signal voltage (high temperature) and scan tester reads 305°F (151°C) or greater, control module and wiring are okay.
3. This test determines if signal circuit is open. There should be 5 volts present at sensor connector if measuring with a DVOM.

Scan tester displays transmission fluid temperature in degrees Centigrade. After transmission is running, displayed temperature should rise steadily to about 100°C then stabilize. A faulty connection or an open in ground circuit or signal circuit will result in a Code 59. Test transmission sensor at various temperature levels to determine if sensor is out of calibration. See TRANSMISSION SENSOR - TEMP TO RESISTANCE chart. An out-of-calibration sensor could result in firm shifts or TCC enabled complaint. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES - GASOLINE article.

TEMPERATURE-TO-RESISTANCE VALUES (1) (2)

Code 59 Flow Chart (All Models) Transmission Fluid Temperature Low. Scheme 352