With 4L60E Automatic Transmission

DTC 59 Transmission Fluid Temperature (TFT) Sensor Circuit High (Low Temperature Indicated):

Transmission Range (TR) Circuit:

CIRCUIT DESCRIPTION
The Transmission Fluid Temperature (TFT) sensor is a thermistor within the Transmission Range (TR) pressure switch assembly, that controls the signal voltage to the Powertrain Control Module (PCM). The PCM applies 5 volts to the sensor on CKT 1227. When the transmission fluid is cold, the sensor resistance is high and the PCM will sense high signal voltage.
As the transmission fluid temperature warms to the normal transmission operating temperature of 100°C (212°F), the sensor resistance becomes less and the voltage decreases at about 1.5 to 2.0 volts.

DTC 59 WILL SET WHEN
Signal voltage indicates TFT less than -40°C (-40°F), for 1 second.

ACTION TAKEN (PCM will default to)
When DTC 59 is set, the transmission will use a warm value for operation, but, the scan tool will display the actual fluid temperature.
When DTC is set, the TCC may not apply properly. DTC 59 will be stored in the PCM memory but will not turn "ON" the MIL (Malfunction Indicator Lamp).

DTC 59 WILL CLEAR WHEN
The fault condition(s) no longer exist.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test checks for a skewed sensor.
2. This test simulates a DTC 58. If the PCM recognizes the low signal voltage (high temperature), and the scan displays 146°C (295°F) or greater, the PCM and wiring are OK.
3. This test checks if CKT 1227 is open. There should be 5 volts present at the sensor connector if measured with J 39200.

DIAGNOSTIC AIDS
Scan tool displays transmission fluid temperature in degrees. After transmission is operating, the temperature should rise steadily to about 100°C (212°F) then stabilize.
A faulty connection or an open in CKT 455 or CKT 1227 can result in a DTC 59.
The "Temperature to Resistance Value" scale may be used to check the TFT sensor at various temperature levels to evaluate the possibility of a "skewed" (mis-scaled) sensor. A "skewed" sensor can result in firm shifts, or TCC complaints.