Circuit Description
The Transmission Fluid Temperature (TFT) sensor is part of the automatic transmission internal wiring harness assembly. The TFT sensor is a thermistor, which is a type of resistor that changes value when the temperature changes. The sensor has a negative temperature coefficient, which means that as the temperature increases, the sensors internal resistance decreases. As the temperature decreases, the sensors internal resistance increases.
The Transmission Control Module (TCM) supplies a 5 volt reference signal to the sensor via terminal X1-15 and measures the voltage drop in the circuit.
When the transmission fluid is cold, the sensor's resistance is high and the TCM detects a high signal voltage. As the fluid temperature increases, the internal resistance of the sensor decreases, which in turn lowers the signal voltage.
If the TCM detects a short to ground in the TFT sensor, or in the signal circuit, then DTC P0712 sets, which is a type 'C' DTC.
Conditions for Running the DTC
| • | Engine running between 450-6,800 RPM for at least 5 seconds. |
| • | Ignition voltage is between 8-18 volts. |
Conditions for Setting the DTC
The TCM detects a TFT resistance of less than 46.18 ohms for 10 seconds.
Action Taken When the DTC Sets
| • | The TCM does not request the Powertrain Interface Module (PIM) to illuminate the Check Powertrain Malfunction Indicator Lamp (MIL). |
| • | The TCM records the operating conditions when the 'Conditions for Setting the DTC' are met. The TCM stores this information as a Failure Record. |
| • | The TCM calculates a default transmission fluid temperature based on engine coolant temperature, intake air temperature and engine run time. |
| • | The TCM freezes the transmission adaptive learning function. |
| • | The TCM stores DTC P0712 into TCM history. |
Conditions for Clearing the DTC
| • | Tech 2 can clear the DTC. |
| • | The TCM clears the DTC from its memory (history DTC) if the vehicle completes 40 warm-up cycles without a non-emission related DTC occurring. |
| • | The TCM cancels the DTC default actions when the fault no longer exists and the DTC passes. |
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
3. This step tests the ability of the TCM to detect an open circuit. If the TCM recognizes the open circuit, this eliminates the TCM and the wiring up to the transmission connector. The fault must be internal to the transmission.
4. As the TFT sensor is an integral part of the transmission internal wiring harness, the entire internal harness must be replaced.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics For information on testing wiring faults, refer to Wiring Systems. | ||||
1 | Has the Diagnostic System Check - Automatic Transmission been completed? | -- | Go to Step 2 | |
2 |
Does the Tech 2 display transmission fluid temperature equal to or greater than the specified value? | 150°C | Go to Step 3 | Go to Testing for Intermittent Conditions and Poor Connections |
3 |
Does the Tech 2 display transmission fluid temperature equal to the specified value? | -40°C | Go to Step 4 | Go to Step 5 |
4 | Replace the transmission internal wiring harness assembly. Refer to Transmission Internal Electrical Harness Replacement for the procedure. Is the replacement complete? | -- | Go to Step 7 | -- |
5 | Using a digital ohmmeter, check the transmission wiring harness TFT signal for a short to ground condition between TCM connector A112_5SPD T68, terminal X1-15 and transmission wiring harness connector X121-_5SPD, terminal X1-10. Does the check indicate a short to ground in the transmission wiring? | -- | Repair short to ground in TFT signal circuit. Go to Step 7 | Go to Step 6 |
6 | Replace the TCM. Refer to Transmission Control Module Replacement. Is the replacement complete? | -- | Go to Step 7 | -- |
7 | Perform the following procedure to verify the repair:
Has the test run and passed? | -- | System OK | Go to Step 2 |
When all diagnosis and repairs are completed, clear all DTCs and verify correct operation. | ||||
