4L80-E / 4L85-E Automatic Transmission

Circuit Description
The Automatic Transmission Fluid Temperature (TFT) sensor is part of the 4L80-E Automatic Transmission (A/T) Wiring Harness Assembly. The TFT sensor is a resistor, or thermistor, which changes value based on temperature. The sensor has a negative-temperature coefficient. This means that as the temperature increases, the resistance decreases, and as the temperature decreases the resistance increases. The Vehicle Control Module (VCM) supplies a 5-volt reference signal to the sensor on circuit 1227 and measures the voltage drop in the circuit. When the transmission fluid is cold, the sensor resistance is high and the VCM detects high signal voltage. As the fluid temperature warms to a normal operating temperature, the resistance becomes less and the signal voltage decreases. The VCM uses this information to control shift quality and Torque Converter Clutch apply.

If the VCM detects a continuous open or short to the power in the TFT signal circuit or the TFT sensor, then DTC P0713 sets. DTC P0713 is a type D DTC.

Conditions for Running the DTC
The ignition is ON.

Conditions for Setting the DTC
^ The TFT sensor indicates a voltage greater than 4.94 volts.
^ All conditions met for 400 seconds.

Action Taken When the DTC Sets
^ The VCM does not illuminate the Malfunction Indicator Lamp (MIL).
^ The VCM commands increased line pressure.
^ The VCM freezes shift adapts.
^ The VCM determines a TFT default Transmission Temperature (TFT) using the following matrix:
- If the engine run time is less than 60 seconds then default TFT equals the Intake Air Temperature (IAT), plus 5 degrees.
- If the Engine Coolant Temperature (ECT) is less than 85°C (185°F) then default TFT equals IAT plus 10 degrees.
- If the ECT is 85° - 110°C (185°-230°F) then default TFT equals ECT plus 10 degrees.
- If the ECT is greater than 110°C (230°F) then default TFT is set to 140°C (284°F) and transmission shift pattern is in hot mode.
- If ECT and TFT DTCs are both set then default TFT is 140°C (284°F).
^ The VCM stores DTC P0713 in VCM history.

Conditions for Clearing the DTC
^ A scan tool clears the DTC from VCM history.
^ The VCM clears the DTC from VCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring.
^ The VCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the VCM.

Diagnostic Aids
^ Inspect the harness for a faulty connection or an open in circuit 1227.
^ Inspect the wiring at the VCM, the transmission connector and all other circuit connecting points for the following conditions:
- A backed out terminal
- A damaged terminal
- Reduced terminal tension
- A chafed wire
- A broken wire inside the insulation
- Moisture intrusion
- Corrosion
^ High voltage (B+) in circuit 1227 may also damage the TFT sensor.
^ When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
^ The scan tool displays the Transmission Fluid Temperature (TFT) in degrees. After the transmission operates, the temperature rises steadily to about 100°C (212°F). The temperature then stabilizes.
^ Test the TFT sensor at the various temperatures in order to evaluate the possibility of a skewed (mis-scaled) sensor. Use the Temperature vs Resistance table. A skewed sensor may cause firm shifts or TCC complaints.
^ First diagnose and clear any engine DTCs or TP sensor codes that are present. Then inspect for any transmission DTCs that may have reset.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
4. This step tests for higher than normal circuit voltage which may also damage the TFT sensor.
6. This step simulates a TFT sensor DTC P0712. If the VCM recognizes the low signal voltage (high temperature), and the scan tool displays 146°C (295°F) or greater, the VCM and the wiring are OK.
7. This step verifies a problem in the TFT sensor circuit inside the transmission.
8. This step inspects the TFT sensor and the automatic transmission wiring harness assembly (A/T wiring harness assembly) for an open Circuit 470 becomes circuit 452 inside the transmission.