4L80-E / 4L85-E Automatic Transmission

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
The Automatic Transmission Fluid Temperature (TFT) sensor is part of the 4L80-E Automatic Transmission (AT) 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 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 short to ground in the TFT sensor or signal circuit, then DTC P0712 sets. DTC P0712 is a type C DTC.

CONDITIONS FOR RUNNING THE DTC
The ignition is ON.

CONDITIONS FOR SETTING THE DTC
^ The TFT sensor indicates a voltage of less than 0.14 volts.
^ All conditions met for 15 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The VCM does not illuminates 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 records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Failure Records.
^ The VCM stores DTC P0712 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
^ First diagnose and clear any engine DTCs or TP sensor codes that are present. Then inspect for any transmission DTCs that may have reset.
^ Inspect the connectors at the VCM, the AT wiring harness and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent and Poor Connections in Diagrams.
^ Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Diagrams.
^ Test the TFT sensor at various temperatures in order to evaluate the possibility of a skewed (mis-scaled) sensor. Use the Transmission Fluid Temperature (TFT) Sensor Specifications table. A skewed sensor may cause delayed garage shifts or TCC complaints.
^ Verify the customer driving habits, trailer towing, weight, or towing in OVERDRIVE.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
3. This step tests for a short to ground or a skewed sensor by verifying the fault still exists.
4. This step tests for an internal fault within the transmission by creating an open.
6. This step inspects circuit 1227 of the AT wiring harness assembly for being shorted to ground.