P0712

Diagnostic Chart:

Wiring Diagram:

Circuit Description

The Automatic Transmission Fluid Temperature (TFT) sensor is a negative coefficient thermister within the Automatic Transmission Fluid Pressure (TFP) Manual Valve Position Switch. The TFT sensor controls the signal voltage from the PCM. The PCM supplies a 5-Volt reference signal to the sensor on circuit 1227. When the transmission fluid is cold, the sensor resistance is high, and the PCM detects high signal voltage. As the transmission fluid temperature increases, the sensor resistance decreases and the detected voltage decreases. At the transmission's normal TFT operating temperature, 100°C (212°F), the voltage is approximately 1.5-2 volts.
If the PCM detects a continuous short to ground in the TFT signal circuit or the TFT sensor, then DTC P071 2 sets. DTC P071 2 is a type D DTC.

Conditions for Setting the DTC
- The system voltage is 10-16 volts.
- The ignition is ON.
- The TFT sensor indicates a voltage less than 0.2 volts.
- All conditions met for 10 seconds.

Action Taken When the DTC Sets
- The PCM freezes shift adapts from being updated.
- The PCM does not illuminate the Malfunction Indicator Lamp (MIL).
- The PCM determines a default Transmission Fluid Temperature (TFT) using the following matrix:

- If any Engine Coolant Temperature (ECT) DTCs P0117, P0118, or P1114, or P1115 are set, then the default TFT is equal to 135°C (275°F).
- If the ECT is 125°C (257°F) or more, then the default TFT is equal to 135°C (275°F).
- If the Engine Run Time is less than 300 seconds, and:
- No Intake Air Temperature (IAT) DTCs P0112 or P0113 are set, and the IAT is available, then the default TFT is equal to the At
- Any Intake Air Temperature (IAT) DTCs P0112 or P0113 are set, or the IAT is not available, then the default TFT is equal to 90°C (194°F).
- If the Engine Run Time is greater than 300 seconds, and no Intake Air Temperature (IAT) DTCs P0112 or P0113 are set, and the IAT is available, and the Engine Coolant Temperature (ECT) is 4-125°C (l0-257°F) and:
- IAT at start up is less than 15°C (59°F), then the default TFT is equal to the Engine Coolant Temperature (ECT) plus 5°C (8°F).
- IAT at start up is greater than 35°C (95°F), then the default TFT is equal to the Engine Coolant Temperature (ECT) plus 10°C (16°F).
- IAT at start up is l5-35°C (5995°F), then the default TFT is equal to the Engine Coolant Temperature (ECT).
- If the Engine Run Time is greater than 300 seconds, and any Intake Air Temperature DTCs P0112 or P0113 are set, or the IAT is not available then the default TFT is equal to the Engine Coolant Temperature (ECT).
- If the Engine Run Time is greater than 300 seconds, and the ECT is less than 40°C (104°F), then the default TFT is equal to 60°C (140°F).

Conditions for Clearing the DTC
- A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.
- The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM.

Diagnostic Aids
- If a transmission fluid overtemperature DTC P0218 is also set, inspect the transmission cooling system for blockage and restrictions.
- Inspect the harness routing for a short to ground in circuit 1227 (YEL/BLK). The scan tool TFT display should rise steadily to about 100°C (212°F), then stabilize.
- Inspect the wiring for poor electrical connections at the PCM. Look for the following problems:

- A bent terminal
- A backed out terminal
- A damaged terminal
- Poor terminal tension
- A chafed wire
- A broken wire inside the insulation

- When diagnosing for an intermittent short or open, massage the wiring harness while watching test equipment for changes.
- Use the Temperature vs Resistance scale in order to test the TFT sensor at various temperatures. Test the TFT sensor in order to eliminate the possibility of a skewed (mis-scaled) sensor. A skewed sensor could result in delayed garage shifts or TCC complaints.
- Inquire about the customer's driving habits, trailer towing, etc.

Test Description

The numbers below refer to the step numbers on the diagnostic chart.

3. This step verifies that a problem exists in the TFT Sensor circuit.
4. This step creates an open. The step uses the open in order to test for an internal fault within the transmission.
6. This step verifies that the resistance of the TFT wiring and the TFT Sensor is within specifications at 20°C (68°F). In order to verify the resistance at other transmission fluid temperatures, you must refer to the 4L60-E TFT vs Resistance chart.