DTC 59

DTC 59 Transmission Fluid Temperature Sensor Circuit:

Fluid Pressure Switch Assembly Circuit:

Circuit Description:
The transmission fluid temperature sensor is a thermistor within the fluid pressure switch assembly, that controls the signal voltage to the 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 normal transmission operating temperature 100°C (212°F), the sensor resistance becomes less and the voltage decreases at about 1.5 to 2.0 volts.
When DTC 59 is set, the transmission will use a warm value for operation, but, the scan tool will display the actual fluid temperature.

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. DTC 59 will set if:
^ Signal voltage indicates a transmission fluid temperature below -33°C (-27°F) for 1 second.
2. This test simulates a DTC 58. If the PCM recognizes the low signal voltage (high temperature), and the scan displays 154° C (309°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 is measured with a J 39200.

Diagnostic Aids:
Scan tool displays transmission temperature in degrees Centigrade. 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 at the right may be used to check the ECT 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 enabled.