LS400 1990-1997

Transmission Fluid Temperature Sensor

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Operation



Specific to:

Lexus LS400 1990-1999

The Transmission Fluid Temperature (TFT) Sensor is a Negative Temperature Coefficient (NTC) Thermistor that monitors the transmission/transaxle fluid (ATF) temperature. The TFT Sensor operates within a 5 volt DC reference range, and provides a linear input signal to the Powertrain Control Module (PCM) that is based upon the measured ATF temperature. The PCM uses data from the TFT Sensor to identify potential problems that may result from excessive fluid temperature such as excessive vehicle load and/or component failure, or an open or short in the TFT circuit.

Removal & Installation



Specific to:

Lexus LS400 1990-1999


CAUTION
When working with FIPG material, you must observe the following items.


CAUTION
Using a razor blade and gasket scraper, remove all the old FIPG material from the gasket surfaces.


CAUTION
Thoroughly clean all components to remove all the loose material.


CAUTION
Clean both sealing surfaces with a non-residue solvent.


CAUTION
Apply FIPG in an approx. 0.04 in. (1 mm) wide bead along the sealing surface.


CAUTION
Parts must be assembled within 10 minutes of application. Otherwise, the FIPG material must be removed and reapplied.

  1. Remove drain plug with gasket and drain ATF
  2.  
  3. Remove oil pan
    NOTE
    Some fluid will remain in the oil pan.

    1. Remove the 19 bolts.
    2.  
    3. Install the blade of SST (SST 09032 - 00100) between the transmission case and oil pan, cut off applied sealer, and remove the oil pan.
      NOTE
      When removing the oil pan, be careful not to damage the oil pan flange.

    4.  

  4.  
  5. Examine particles in pan
    1. Remove the magnets and use them to collect steel particles.
    2.  
    3. Carefully look at the foreign matter and particles in the pan and on the magnets to anticipate the type of wear you will find in the transmission.

      Steel (magnetic) bearing, gear and clutch plate wear
       
      Brass (non-magnetic) bushing wear
       

    4.  

  6.  
  7. Remove oil strainer
    NOTE
    Be careful as some fluid will come out of the oil strainer.

    1. Remove the 4 bolts and oil strainer.
    2.  
    3. Remove the 3 gaskets from the oil strainer.
    4.  

  8.  
  9. Remove solenoid wiring with ATF temperature sensor
    1. Disconnect the ATF temperature sensor.
    2.  
    3. Remove the bolt and clamp.
    4.  
    5. Disconnect the 7 connectors from the solenoid valves.
    6.  
    7. Remove the bolt and pull out the solenoid connector.
    8.  

  10.  

To install:

  1. Install solenoid wiring with atf temperature sensor
    1. Install the solenoid connector with the bolt. Tighten the bolt to 48 inch lbs. (5.4 Nm).
    2.  
    3. Connect the 7 connectors to the solenoid valves.
    4.  
    5. Install the clamp with the bolt. Tighten the bolt to 56 inch lbs. (6.4 Nm)
    6.  
    7. Connect the ATF temperature sensor.
    8.  

  2.  
  3. Install oil strainer
    1. Install 3 new gaskets.
    2.  
    3. Install the oil strainer with the 4 bolts. Tighten the bolts to 84 inch lbs. (10 Nm)
    4.  

  4.  
  5. Install oil pan
    1. Install the 3 magnets in the indications of the oil pan.
    2.  
    3. Remove any packing material and be careful not to drop oil on the contacting surfaces of the transmission case and oil pan.
    4.  
    5. Apply FIPG to the oil pan. FIPG: Part No. 08826 - 00090, THREE BOND 1281 or equivalent
    6.  
    7. Install the oil pan with the 19 bolts. Tighten the bolts to 65 inch lbs. (7.4 Nm)
    8.  

  6.  
  7. Install drain plug with new gasket. Tighten the drain plug to 15 ft. lbs. (20 Nm)
  8.  
  9. Fill fluid and check fluid
  10.  

Testing



Specific to:

Lexus LS400 1990-1999


NOTE
Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.

Connection & Wiring Diagnosis

Specific to:

Lexus LS400 1990-1999

Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.

Many intermittent open or short circuits may be caused by wiring harness and connector movement due to vibration, engine torque, bumps and rough pavement, etc.

  1. Test the wiring harness and connectors by performing the following tests:

    Move the related connectors and wiring while monitoring the appropriate scan tool data.
     
    Move the related connectors and wiring with the component commanded ON and OFF. Using a suitable the scan tool, observe the component operation.
     
    With the engine running, move the related connectors and wiring while monitoring component operation.
     
    If harness or connector movement affects the data displayed, the component and system operation, or the engine operation, inspect and repair the harness or connections as necessary.
     

  2.  
  3. Test the connector terminal pins and/or wiring by performing the following tests:

    Inspect for incorrect mating of the connector halves, or terminals not fully seated in the connector body.
     
    Inspect for improperly formed or damaged terminals and test for incorrect terminal tension.
     
    Inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body.
     
    Inspect for corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and/or brittle sections of wire in the suspect circuits.
     
    Inspect for wires that are broken inside the insulation by gently pulling on suspect sections of wiring.
     

  4.  

Related Diagnostic Trouble Codes

Specific to:

Lexus LS400 1990-1999



Click image to see an enlarged view

Fig. Related Diagnostic Trouble Codes

TFT Circuit Testing

Specific to:

Lexus LS400 1990-1999

Use a suitable scan tool, a Graphing Multi-Meter (GMM), or a Digital Volt-Ohm Meter (DVOM) in order to view the TFT data.

TFT Sensor logic is relative to the scale of resistance: when the ATF temperature is low, the voltage is increased. When the ATF temperature is high, the voltage is decreased.

Inspect the vehicle for ATF leaks, check the fluid level and condition, and verify that the transmission/transaxle assembly does not display signs of physical damage. If there are significant ATF leaks, if the fluid level is low or is contaminated, or if transmission/transaxle case damage is evident, note your findings and evaluate if service-related and/or mechanical repairs are in order before continuing.

If a DVOM is being used, additional information may be acquired by taking measurements at the sensor connector as well as the PCM connector. If a significant voltage drop is measured (greater than 0.5 volts DC), check the wiring harness and connections for corrosion, poor pin connections, or damaged wires.

If all engine wiring and pin connections are confirmed, disconnect the TFT Sensor to verify the signal with a DVOM, and verify PCM communication before replacing the TFT Sensor.

Click image to see an enlarged view

Fig. TFT Range Chart

TFT Sensor Strategy

Specific to:

Lexus LS400 1990-1999

The TFT Sensor provides a linear input signal to the Powertrain Control Module (PCM), which is used to monitor the ATF temperature. If the TFT reference value is less than 0.2 volts DC (302°F) or greater than 5.0 volts DC (-40°F), the PCM interprets this as an abnormal ATF temperature condition, or a fault in the TFT circuit. Under these conditions, the engine Malfunction Indicator Lamp (MIL) will illuminate and a DTC will be stored. Some systems utilize a separate MIL, which is specifically dedicated to automatic transmission/transaxle temperature.

 
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