Diagnostic Aids

Scan tester displays transmission temperature in degrees Centigrade. After transmission is running, the displayed temperature should rise steadily to about 212°F (100°C) then stabilize. A faulty connection or an open in circuit No. 455/452 or circuit No. 1227 will result in a Code 59. Test the coolant sensor at various temperature levels to determine if sensor is out of calibration. See TRANSMISSION SENSOR - TEMPERATURE TO RESISTANCE chart. An out-of-calibration sensor could result in firm shifts, or TCC enabled complaint.

Fig 1: CODE 59, Schematic, Trans. Temp. Sensor Circuit Low

Courtesy of GENERAL MOTORS CORP.

Fig 2: CODE 59, Flow Chart, Trans. Temp Sensor Circuit Low

Courtesy of GENERAL MOTORS CORP.