Circuit Description
The automatic transmission fluid temperature (TFT) sensor is part of the automatic transmission fluid pressure (TFP) manual valve position switch. The TFT sensor is a resistor, or thermistor, which changes value based on temperature. 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 vehicle control module (VCM) supplies a 5-volt reference signal to the sensor on circuit 1227 and measures the voltage drop in the circuit. When the transmission fluid is cold, the sensor resistance is high and the VCM detects high signal voltage. As the fluid temperature warms to a normal operating temperature, the resistance becomes less and the signal voltage decreases. The VCM uses this information to control shift quality and torque converter clutch apply.
When the VCM detects a continuous short to ground in the TFT signal circuit or in the TFT sensor, then DTC P0712 sets. DTC P0712 is a type C DTC.
Conditions for Running the DTC
| • | The system voltage is 10-19 volts. |
| • | The ignition switch is in the RUN position. |
Conditions for Setting the DTC
The TFT sensor indicates a signal voltage less than 0.2 volts for 10 seconds.
Action Taken When the DTC Sets
| • | The VCM does not illuminate the malfunction indicator lamp (MIL). |
| Important: The scan tool does not indicate the default TFT. |
| Important: The actions listed below are in order of highest to lowest priority. |
| • | The VCM determines a default TFT using one of the following: |
| 1. | If any ECT DTCs P0117 or P0118 are set, then the default TFT is equal to 135°C (275°F). |
| 2. | If the ECT is 125°C (257°F) or more, then the default TFT is equal to 135°C (275°F). |
| 3. | If the engine run time is less than 300 seconds and: |
| • | No intake air temperature (IAT) DTCs P0112 or P0113 are set and IAT is available, then the default TFT is equal to IAT. |
| • | Any IAT DTCs P0112 or P0113 are set or IAT is NOT available, then the default TFT is equal to 90°C (194°F). |
| 4. | If the engine run time is greater than 300 seconds and no IAT DTCs P0112 or P0113 are set and IAT is available and ECT is between 40 and 125°C (104 and 257°F) and: |
| • | IAT at startup is less than 15°C (59°F), then the default TFT is equal to the ECT plus 5°C (8°F). |
| • | IAT at startup is greater than 35°C (95°F), then the default TFT is equal to the ECT plus 10°C (16°F). |
| • | IAT at startup is between 15 and 35°C (59 and 95°F), then the default TFT is equal to the ECT. |
| 5. | If the engine run time is greater than 300 seconds and any IAT DTCs P0112 or P0113 are set or IAT is NOT available, then the default TFT is equal to the ECT. |
| 6. | If the engine run time is greater than 300 seconds and ECT is less than 40°C (104°F) or more, then the default TFT is equal to 60°C (140°F). |
| • | The VCM freezes shift adapts from being updated. |
| • | The VCM records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Failure Records. |
| • | The VCM stores DTC P0712 in VCM history. |
Conditions for Clearing the DTC
| • | A scan tool can clear the DTC. |
| • | The VCM clears the DTC from VCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring. |
| • | The VCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the VCM. |
Diagnostic Aids
| • | Inspect the wiring at the VCM, the transmission connector and all other circuit connecting points for the following conditions: |
| - | A backed out terminal |
| - | A damaged terminal |
| - | Reduced 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. |
| • | The scan tool displays the transmission fluid temperature in degrees. After the transmission is operating, the fluid temperature should rise steadily to a normal operating temperature, then stabilize. |
| • | Verify the customer's driving habits, trailer towing, etc. Trailer towing should occur in D3. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for a short to ground condition.
-
This step tests for an internal fault within the transmission by creating an open.
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 | Perform the transmission fluid checking procedure. Refer to Transmission Fluid Check . Was the fluid checking procedure performed? | -- | Go to Transmission Fluid Check | |
Important: Before clearing the DTC, use the Scan Tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the VCM. Does the Scan Tool display a TFT Sensor signal voltage greater than the specified value? | 0.2 V | Go to Diagnostic Aids | ||
Does the Scan Tool display a TFT Sensor signal voltage greater than the specified value? | 4.92 V | |||
5 |
Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance within the specified range? | 3088-3942 ohms at 20°C (68°F) 159-198 ohms at 100°C (212°F) | Go to Diagnostic Aids | |
6 | Inspect circuit 1227 (BRN) of the automatic transmission (A/T) wiring harness assembly for a short to ground condition. Refer to Circuit Testing in Wiring Systems. Did you find a short to ground condition? | -- | ||
7 |
Refer to Circuit Testing in Wiring Systems. Refer to Wiring Repairs in Wiring Systems. Did you find a short to ground condition? | -- | ||
8 | Replace the TFT sensor (this sensor is part of the TFP manual valve position switch). Refer to Valve Body . Is the replacement complete? | -- | -- | |
9 | Replace the AT wiring harness assembly. Refer to Valve Body . Is the replacement complete? | -- | -- | |
10 | Replace the VCM. Refer to VCM Replacement/Programming in Engine Controls. Is the replacement complete? | -- | -- | |
11 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
