Circuit Description
The Automatic Transmission Fluid Temperature (TFT) Sensor is a thermistor that controls the signal voltage to the Transmission Control Module (TCM). The TCM supplies a 5 volt reference signal to the sensor on circuit 1227. When the transmission fluid is cold, the sensor resistance is high and the controller will sense high signal voltage.
As the transmission fluid temperature warms to normal transmission operating temperature, the sensor resistance becomes less and the voltage decreases. With a DTC 79 also set, check the transmission cooling system.
If the TCM detects a continuous short to ground in the TFT signal circuit, then DTC 59 sets.
Conditions for Setting the DTC
| • | Signal voltage indicates TFT less than -40°C (-40°F). |
| • | All conditions met for 1 second. |
Action Taken When the DTC Sets
| • | The TCM does not illuminate the Malfunction Indicator Lamp MIL. |
| • | The TCM will default to 140°C for a Trans. Fluid Temperature (causing a hot mode shift pattern to occur). |
| • | DTC 59 is stored in TCM history. |
Conditions for Clearing the DTC
| • | The TCM clears the DTC from Current to History when the fault condition(s) no longer exist and the ignition switch is cycled OFF and then ON. |
| • | A scan tool can clear the DTC from Current and History status. The TCM clears the DTC from the TCM history if the vehicle completes 40 ignition cycles without a failure reported. |
| • | The TCM cancels the DTC default actions when the fault no longer exists and the ignition is cycled OFF and then ON. |
Diagnostic Aids
| • | Inspect the harness for a faulty connection or an open in circuit 1227. |
| • | Inspect the wiring at the TCM, 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 |
| - | Higher than normal voltage in circuit 1227 may also damage the TFT Sensor. |
| • | When diagnosing for an intermittent short or open, 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 operates, the temperature rises steadily. The temperature then stabilizes. |
| • | Test the TFT Sensor at the various temperatures in order to evaluate the possibility of a skewed (mis-scaled) sensor. Use the Temperature vs Resistance table. A skewed sensor may cause firm shifts or TCC complaints, extended shift patterns, and early TCC applies to occur. |
| • | First diagnose and clear any engine DTCs that are present. Then inspect for any transmission DTCs that may have reset. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for higher than normal circuit voltage which may also damage the TFT Sensor.
-
This step simulates a TFT Sensor DTC 58. If the TCM recognizes the low signal voltage (high temperature), and the Scan Tool displays 146° C (295° F) or greater, the TCM and the wiring are OK.
-
This step verifies a problem in the TFT Sensor circuit.
-
This step inspects the TFT Sensor and the A/T Wiring Harness Assy.
-
The TFT Sensor is part of the A/T Wiring Harness Assy.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 | Perform the Transmission Fluid Checking Procedure. Refer to Transmission Fluid Check . Did you perform the fluid checking procedure? | -- | Perform the Transmission Fluid Check | |
3 |
Important:: Before clearing the DTC's, record the Current and History DTC's information for reference. The Clear Info function erases the stored Current and History DTC from the TCM. Does the Scan Tool display a transmission fluid temperature less than the specified value? | -30° C (-22° F) | Go to Diagnostic Aids | |
4 |
Is the voltage within the specified value? | 4.9 - 5.0 volts | ||
|
Important:: Refer to Test Description for information about Step 4. Is the J 39200 DMM voltage greater than the specified value? | 5.1 volts | |||
Is the transmission fluid temperature greater than the specified value? | 140° C (284° F) | |||
Is the resistance within the specified values? | 16 kohms at 10° C (50° F) to 133ohms at 110° C (230° F) | Go to Diagnostic Aids | ||
Was the condition found and corrected? | -- | Go to Diagnostic Aids | ||
Replace the A/T Wiring Harness Assy. Refer to 4L80-E On-Vehicle Service, Interior Wiring Harness Assy. Replacement. Is the replacement complete? | -- | |||
10 | Inspect circuit 1227 for high resistance or an open. Refer to General Electrical Diagnosis . Was the condition found and corrected? | -- | ||
11 | Inspect circuit 1227 for a short to voltage B +. Refer to General Electrical Diagnosis . Was the condition found and corrected? | -- | ||
12 | Inspect circuit 470/452 for an open. Refer to General Electrical Diagnosis . Was the condition found and corrected? | -- | ||
13 | Inspect the TCM for faulty or intermittent connections. Was the condition found and corrected? | -- | ||
14 | Replace the TCM. Refer to DTC 51 PROM Error TCM Replacement. Is the replacement complete? | -- | -- | |
15 | In order to verify your repair, perform the following procedure:
Is the transmission fluid temperature greater than -40° C (-40° F). | -- | System OK | Begin diagnosis again |
