For 1990-2009 cars

### Circuit Description

The automatic transmission fluid temperature (TFT) sensor is part of the automatic transmission internal wiring harness assembly. The TFT sensor is a thermistor, or a resistor that changes value when the temperature changes. 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 transmission control module (TCM) 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 TCM detects high signal voltage. As the fluid temperature increases, the resistance of the sensor decreases, which lowers the signal voltage.

If the TCM detects a short to ground in the TFT sensor or signal circuit, then DTC P0712 sets. DTC P0712 is a type A DTC.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0712 Transmission Fluid Temperature (TFT) Sensor Circuit Low Voltage

### Conditions for Running The DTC

• | Trans. Protection Mode is OFF.

• | The engine run time is 5 seconds or greater.

• | The ignition voltage is 8-18 volts.

### Conditions for Setting The DTC

The TCM detects a transmission fluid temperature of 150°C (302°F) or more for 5 minutes.

### Action Taken When the DTC Sets

• | The TCM requests the powertrain control module (PCM) to illuminate the malfunction indicator lamp (MIL).

• | DTC P1719 is disabled.

• | No lock-up slip neutral control or uphill/downhill control until transmission fluid temperature is greater than 40°C (104°F) for 5 seconds.

• | The TCM discontinues updating the transmission adaptive pressure (TAP) memory cells, until engine run time is at least 30 minutes.

• | The TCM uses 30°C (86°F) as a default transmission fluid temperature.

• | The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.

• | 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 stores DTC P0712 in TCM history.

### Conditions for Clearing the MIL/DTC

• | The TCM turns OFF the MIL request during the third consecutive trip in which the diagnostic test runs and passes.

• | A scan tool can clear the DTC.

• | The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.

• | The TCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the TCM.

### Test Description

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

1. This step tests the ability of the TCM to detect an open circuit. If the TCM recognizes the open, this eliminates the TCM and the wiring up to the transmission connector. The fault must be internal to the transmission.

2. Because the TFT is an integral part of the transmission wiring, the entire harness must be replaced.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.

Important:

• | Before clearing the DTC, use the scan tool in order to record the PCM and the TCM Failure Records. Using the Clear Eng./Trans. DTC Info function erases the Failure Records from the powertrain control module (PCM) and the transmission control module (TCM).

• | Using the Clear Eng./Trans. DTC Info function erases stored DTCs in both the PCM and TCM.

3. Record the Failure Records.
4. Clear the DTCs.
5. Select Trans. Fluid Temp. on the scan tool.

Does the scan tool display transmission fluid temperature equal to or greater than the specified value?

150°C (302°F)

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections

3 |

1. Turn OFF the ignition.
2. Disconnect the automatic transmission 14-way harness connector. Additional DTCs may set.
3. Turn ON the ignition, with the engine OFF.

Does the scan tool display transmission fluid temperature equal to the specified value?

-40°C (-40°F)

Go to Step 5

Go to Step 4

4 | Test the Transmission Fluid Temperature sensor signal circuit from the transmission 14-way harness to the TCM for a short to ground. Refer to Testing for Short to Ground . Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 6
5 | Replace the automatic transmission internal wiring harness assembly. Is the action complete? | -- | Go to Step 7 | --
6 | Replace the TCM. Refer to Control Module References for replacement, setup, and programming. Is the action complete? | -- | Go to Step 7 | --
7 | Perform the following procedure in order to verify the repair:

1. Select DTC.
2. Select Clear Info.
3. Start the engine and verify the following conditions:

• | The Trans. Fluid Temp. must be between 0-150°C (32-302°F) for 5 minutes.

• | The Trans. Fluid Temp. must change by greater than 5°C (41°F) since engine start-up.

4. Select Specific DTC.
5. Enter DTC P0712.

Does the DTC reset?

150°C (302°F)

Go to Step 2

Go to Step 8

8 | With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK