Circuit Description
The Automatic Transmission Fluid Temperature (TFT) sensor is a negative coefficient thermistor. When the transmission fluid is cold, the sensor resistance is high. As the transmission fluid warms, the sensor resistance decreases. The TFT range is -40 to +150°C (-40 to +302°F).
The PCM provides a 5 volt reference through a fixed resistor to the TFT circuit and monitors the voltage after the resistor as the voltage drop (signal) across the TFT circuit.
When the PCM detects a continuous voltage input of less than 0.20 V, indicating a short to ground in the TFT Sensor circuit, then DTC P0712 sets. DTC P0712 is a type D DTC.
Conditions for Setting the DTC
| • | System voltage is 10-16 volts. |
| • | The ignition is ON. |
| • | The PCM detects a TFT sensor voltage of 0.20 volts or less for 10 seconds. |
Action Taken When the DTC Sets
| • | The PCM does not illuminate the Malfunction Indicator Lamp (MIL). |
| • | If the Engine Run Time is less than 3 minutes and: |
| - | The Intake Air Temperature (IAT) DTC(s) P0112, P0113, P1111 or P1112 is set, then the default Automatic Transmission Fluid Temperature (TFT) is set to 0°C (32°F). |
| - | No IAT DTC is set, then the TFT is set to the IAT value which was saved at start up. |
| • | If the engine run time is greater than 3 minutes and: |
| - | The Engine Coolant Temperature (ECT) DTC(s) P0117, P0118, 1114 or P1115 is set, then the default TFT is set to 131°C (268°F). |
| - | No ECT DTC is set and: |
| • | The ECT is less than 45°C (113°F), then the default TFT is set to 12°C (54°F). |
| • | The ECT is greater than 115°C (239°F), then the default TFT is set to 131°C (268°F). |
| - | No ECT DTC is set, the ECT is 45-115°C (113-239°F) and: |
| • | The IAT DTC(s) 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 the ECT value minus 10°C (18°F). |
| • | The IAT at start up is greater than 28°C (82°F), then the default TFT is set to the ECT value plus 10°C (18°F). |
| • | The IAT at start up is 0-28°C (32-82°F), then the default TFT is set equal to the ECT value. |
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 at the PCM, the transmission connector and all other circuit connecting points for the following conditions: |
| - | A bent terminal |
| - | A backed out terminal |
| - | A damaged terminal |
| - | Poor terminal tension |
| - | A chafed wire |
| - | A broken wire inside the insulation |
| - | Moisture intrusion |
| - | Corrosion |
| • | When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change. |
| • | Inspect the transmission harness for a short to ground. Inspect the engine harness for a short to ground. |
| • | Inspect the transmission cooling system for blockage or other restrictions. |
| • | Refer to the Temperature vs Resistance (TFT) Chart. |
| • | Test the TFT Sensor at various temperature levels to check for a skewed (mis-scaled) sensor. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
A scan tool display of less than 0.2 volts indicates that this DTC is current.
-
This action isolates the fault between the transmission harness and the engine harness.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||
2 | Have you performed the Transmission Fluid Checking Procedure? | -- | Go to Transmission Fluid Check | |||||
Important: Before clearing the DTCs, use the scan tool in order to record the Failure Records for reference. The Clear Info function will erase the stored Failure Records from the PCM. Does the scan tool display TFT Sensor voltage less than the specified value? | 0.20 volts | Go to Diagnostic Aids | ||||||
Important: With the ignition ON for more than 10 seconds, the PCM will go to a default transmission temperature. Does the scan tool display a TFT Sensor voltage greater than the specified value? | 4.9 volts | |||||||
5 | Inspect circuit 1227 of the engine harness for a short to ground. Refer to General Electrical Diagnosis . Was a condition found and corrected? | -- | ||||||
6 |
Does the DMM display a resistance greater than that specified? | 100k ohms | ||||||
7 |
Is the resistance below the specified value? | 100kohms | ||||||
8 | Replace the Automatic Transmission Wiring Harness. Refer to Solenoids and Wiring Harness Replacement . Is the replacement complete? | -- | -- | |||||
9 | Replace the TFT Sensor. Refer to Fluid Temperature Sensor Replacement . Is the replacement complete? | -- | -- | |||||
10 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the replacement complete? | -- | -- | |||||
11 | In order to verify your repair, perform the following procedure:
Has the test run and passed? | -- | System OK |
