Circuit Description
The Automatic Transmission Fluid Temperature (TFT) sensor is a negative coefficient thermistor whose resistance value changes based on temperature. The PCM provides a 5 volt reference to the sensor on circuit 1227. A high fluid temperature or a short to ground on circuit 1227 results in low signal voltage. The TFT operating range is -40 to +151°C (-40 to +304°F).
If the PCM detects a continuous short to ground in the TFT sensor circuit, then DTC P0712 sets. DTC P0712 is a type D DTC.
Conditions for Setting the DTC
| • | The system voltage is 9-16 volts. |
| • | The ignition is ON. |
| • | The PCM detects a TFT sensor voltage of 0.200 volts or less for 10 seconds. |
Action Taken When the DTC Sets
| • | The PCM does not turn on the Malfunction Indicator Lamp (MIL). |
| • | The PCM disables shift adapts. |
| • | The default TFT will be determined through the following calculations: |
| - | If the Engine Run Time is less than 3 minutes and: |
| • | Intake Air Temperature (IAT) DTC P0112, P0113, P1111 or P1112 is set, then the default TFT is 0°C (32°F). |
| • | No IAT DTC is set, then the default TFT is set to the IAT saved at start up. |
| - | If the Engine Run Time is greater than 3 minutes, and the Engine Coolant Temperature (ECT) DTC P0117, P0118, P1114 or P1115 is set, then the default TFT is 131°C (268°F). |
| - | If the Engine Run Time is greater than 3 minutes, no ECT DTC is set and: |
| • | The ECT is less than 45°C (113°F), then the default TFT is 12°C (54°F). |
| • | The ECT is greater than 115°C (239°F), then the default TFT is 131°C (268°F). |
| • | The ECT is 45-115°C (113-239°F) and: |
| - | The IAT DTC P0112, P0113, P1111 or P1112 is set, then the default TFT is set to equal the ECT. |
| - | The IAT at start up is less than 0°C (32°F), then the default TFT is set to ECT minus 10°C (18°F). |
| - | The IAT at start up is greater than 28°C (82°F), then the default TFT is set to ECT plus 10°C (18°F). |
| - | The IAT at start up is 0-28°C (32-82°F), then the default TFT is set to equal ECT. |
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
| • | Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring for poor electrical connections at the transmission 20-way connector. Look for the following conditions: |
| - | A bent terminal |
| - | A backed out terminal |
| - | A damaged terminal |
| - | Poor terminal tension |
| - | A chafed wire |
| - | Moisture Intrusion |
| • | When diagnosing for an intermittent short to ground or short to power, massage the wiring harness while watching the test equipment for a change. |
| • | Test the TFT sensor at various temperature levels to evaluate the possibility of a skewed (mis-scaled) sensor. Refer to the Temperature vs Resistance table. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the PCM's ability to detect an open circuit.
-
This step tests the TFT sensor for correct resistance.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls | |||||
2 |
Important: Before clearing the DTCs, use the Scan Tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the PCM. Does the Scan Tool display a TFT sensor voltage less than specified? | 0.2 volts | Go to Diagnostic Aids | |||||
Does the Scan Tool display a TFT sensor voltage greater than specified? | 4.92 volts | |||||||
4 | Inspect circuit 1227 from the engine 20-way connector to the PCM connector for a short to ground. Refer to General Electrical Diagnosis in Wiring Systems. Was the condition found? | -- | ||||||
Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance within the range specified for the given transmission temperatures? | 20°C (68°F) 3,106-3,923 ohms 100°C (212°F) 164-190 ohms | |||||||
6 | Measure the resistance between terminal L and a good ground on the transmission case. Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance less than the specified value? | 1,000 ohms | Go to Diagnostic Aids | |||||
7 |
Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance less than the specified value? | 1,000 ohms | ||||||
8 | Repair the wiring as necessary. Is the repair complete? | -- | -- | |||||
9 | Replace the TFT sensor. Refer to Fluid Temperature Sensor Replacement . Is the replacement complete? | -- | -- | |||||
10 | Replace the automatic transmission wiring harness. Refer to Solenoids and Wiring Harness Replacement . Is the replacement complete? | -- | -- | |||||
11 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming in Engine Controls. Is the replacement complete? | -- | -- | |||||
12 | Perform the following procedure In order to verify the repair:
Has the test run and passed? | -- | System OK |
