With 4L80E Transmission

Transmission Fluid Temperature (TFT) Sensor Circuit Low (High Temp Ind):

CIRCUIT DESCRIPTION
The Transmission Fluid Temperature (TFT) sensor is a thermistor that controls the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a 5 volt reference signal 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 normal transmission operating temperature of 100°C (212°F), the sensor resistance becomes less and the voltage decreases to approximately 1.5 to 2.0 volts. With a Diagnostic Trouble Code (DTC) 79 also set, check the transmission cooling system.

DTC 58 WILL SET WHEN
- Signal voltage indicates TFT greater than 150°C (306°F).
- All conditions met for 1 second.

ACTION TAKEN (PCM WILL DEFAULT TO)
The PCM will use a warm default trans fluid temperature value.

DTC 58 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 short to ground or a skewed sensor.
2. This test checks for an internal fault within the transmission by creating an open.

DIAGNOSTIC AIDS
- Check harness routing for a potential short to ground in CKT 1227.
- Scan tool TFT displays should rise steadily to about 100°C (212°F) then stabilize.
- The temperature to resistance value scale may be used to test the TFT sensor at the various temperature levels to evaluate the possibility of a "skewed" sensor. A "skewed" (mis-scaled) sensor could result in delayed garage shifts or Torque Converter Clutch (TCC) complaints.