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    Ford Probe 1989-1992 Repair Guide

    Temperature Sensors

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    OPERATION



    The Air Charge Temperature (ACT) and Engine Coolant Temperature (ECT) sensors change resistance according to temperature change. ACT and ECT sensor resistance decreases as the surrounding temperature increases, providing a signal to the ECA that indicates either the temperature of the incoming air charge or engine coolant temperature. If the ACT or ECT sensor malfunctions, the lack of accurate temperature information could cause the ECA to provide output information resulting in an incorrect air/fuel ratio. This could cause poor vehicle performance and/or emission test failure.

    SERVICE



    2.2L Engine

    ACT SENSOR

    1989 Vehicles


    WARNING
    The ambient temperature must be above 50°F (10°C) for this test.

    1. Visually inspect all wiring, wiring harnesses, connectors and components for evidence of overheating, insulation damage, looseness, shorting or other damage and repair, as required. If everything looks okay, go to Step 2.
    2.  
    3. Check sensor resistance as follows:
    4.  

    1. Turn the ignition key OFF .
    2.  
    3. Install the breakout box according to the manufacturers instructions, leaving the ECA disconnected.
    4.  
    5. Place the volt-ohmmeter on the 100,000 ohm; scale.
    6.  
    7. Measure the resistance between test pin 25 and pin 46 (Refer to Fig. 36).
    8.  
    9. At 4°F ({155}20°C), the resistance should be 13600-18400 ohms;. At 68°F (20°C), the resistance should be 2210-2690 ohms;. At 140°F (60°C), the resistance should be 493-667 ohms;.
    10.  
    11. If the resistance reading is within specification, go to Step 2. If it is not, go to Step 6.
    12.  
    13. Check the sensor voltage as follows:
    14.  

    1. Install the breakout box according to the manufacturers instructions.
    2.  
    3. Place the volt-ohmmeter on the 10 volt scale.
    4.  
    5. Turn the ignition key ON .
    6.  
    7. Measure the voltage between pin 25 and pin 20. At 68°F (20°C), it should be 2.5 volts.
    8.  
    9. Measure the voltage between pin 46 and ground pin 20. At 68°F (20°C), it should be 0 volts.
    10.  
    11. If all voltage readings are within specification, replace the ECA. If they are not, go to Step 4.
    12.  


    WARNING
    Voltage decreases while temperature increases.

    1. Check for a short between the sensor and the ECA as follows:
    2.  
    3. Turn the ignition key OFF and disconnect the negative battery cable.
    4.  
    5. Install the breakout box according to the manufacturers instructions, leaving the ECA disconnected.
    6.  
    7. Place the volt-ohmmeter on the 200 ohm; scale and measure the resistance between the following pins:

      pin 25 and pin 26
       
      pin 25 and pin 1
       
      pin 25 and pin 37
       
      pin 25 and ground pin 20
       
      pin 46 and pin 26
       
      pin 46 and pin 1
       
      pin 46 and pin 37
       

    8.  
    9. If any resistances are below 5 ohms, repair the wire(s) in question. If no resistances are below 5 ohms, go to Step 5.
    10.  
    11. Check the signal return as follows:
    12.  

    1. Turn the ignition key OFF .
    2.  
    3. Install the breakout box according to the manufacturers instructions.
    4.  
    5. Place the volt-ohmmeter on the 200 ohm; scale and measure the resistance between pin 46 and ground pin 20.
    6.  
    7. If the resistance is below 5 ohms, replace the ECA. If the resistance is not below 5 ohms, check the reference voltage and signal return circuits in the sensor harness.
    8.  
    9. Check for opens between the sensor and the ECA as follows:
    10.  

    1. Turn the ignition key OFF .
    2.  
    3. Install the breakout box according to the manufacturers instructions, leaving the ECA disconnected.
    4.  
    5. Place the volt-ohmmeter on the 200 ohm scale and measure the resistance between pin 25 and VAF R wire pin 46 and VAF light GN/Y wire.
    6.  
    7. If all resistances are below 5 ohms, go to Step 7. If all resistances are not below 5 ohms, repair the wire(s) in question.
    8.  
    9. Check the sensor resistance as follows:
    10.  
    11. Turn the ignition key OFF .
    12.  
    13. Disconnect the sensor connector.
    14.  
    15. Place the volt-ohmmeter on the 10K ohm scale.
    16.  
    17. At 68°F (20°C), measure the resistance between the sensor terminals D and G and between terminals C and G.
    18.  
    19. If the resistances are between 2000-2700 ohms, repair the short in the R wire. If the resistances are not between 2000-2700 ohms, replace the VAF meter.
    20.  

    1990-92 Vehicles

    1. Check the sensor input voltage as follows:
    2.  
    3. Install breakout box tool T83L-50-EEC-IV or equivalent and leave the ECA connected.
    4.  
    5. Access the temperature sensor in the VAF meter. Monitor the temperature near the sensor.
    6.  
    7. Turn the ignition key ON .
    8.  
    9. Measure the voltage between test pin VAT and test pin SIGRTN.
    10.  
    11. Compare the voltage readings to the specifications in Fig. 2 as the temperature sensor is heated.
    12.  


    WARNING
    If using a hot air gun to heat the sensor, be careful not to melt any plastic or rubber components.

    1. If the voltage readings are incorrect, proceed to Step 2.
    2.  
    3. Check the air temperature sensor input resistance as follows:

      Turn the ignition key OFF .
       
      Leave the breakout box connected, but disconnect the ECA.
       
      Access the temperature sensor in the VAF meter. Monitor the temperature near the sensor.
       
      Measure the resistance between test pin VAT and test pin SIGRTN.
       
      Compare the resistance readings to the specifications in Fig. 2 as the temperature sensor is heated.
       

    4.  


    WARNING
    If using a hot air gun to heat the sensor, be careful not to melt any plastic or rubber components.

    1. If the resistance readings are okay, proceed to Step 3. If not, proceed to Step 4.
    2.  
    3. Check the sensor circuit isolation as follows:
    4.  
    5. Turn the ignition key OFF .
    6.  
    7. Leave the breakout box connected, but disconnect the ECA.
    8.  
    9. Disconnect the VAF meter connector.
    10.  
    11. Measure the resistance between test pin VAT and all other test pins.
    12.  
    13. If any resistances are less than 5 ohms, service the temperature sensor wire to the VAF meter. If not, replace the ECA.
    14.  
    15. Check temperature sensor resistance as follows:
    16.  

    1. Turn the ignition key OFF .
    2.  
    3. Disconnect the VAF meter connector.
    4.  
    5. Access the temperature sensor in the VAF meter. Monitor the temperature near the sensor.
    6.  
    7. Measure the resistance between the VAF meter VAT terminal and the VAF meter SIGRTN terminal (where these wires were).
    8.  
    9. Compare the resistance readings to the specifications in Fig. 2 as the temperature sensor is heated.
    10.  


    WARNING
    If using a hot air gun to heat the sensor, be careful not to melt any plastic or rubber components.

    If the resistance readings are okay, service the VAF meter VAT and/or SIGRTN wires to the ECA. If not, replace the VAF meter.



    Click image to see an enlarged view

    Fig. Fig.1ACT sensor test pin identification 1990-92 2.2L engine



    Click image to see an enlarged view

    Fig. Fig. 2 ACT sensor testing data 1990-92 2.2L engine

    ECT SENSOR

    1989 Vehicles

    1. Visually inspect all wiring, wiring harnesses, connectors and components for evidence of overheating, insulation damage, looseness, shorting or other damage and repair, as required. If everything looks okay, go to Step 2.
    2.  
    3. Check the ECT sensor resistance as follows:
    4.  
    5. Turn the ignition key OFF .
    6.  
    7. Install the breakout box according to the manufacturers instructions, leaving the ECA disconnected.
    8.  
    9. Place the volt-ohmmeter on the 200 ohm scale and measure the resistance between pin 7 and pin 46.
    10.  
    11. At {155}4°F ({155}20°C), the resistance should be 14500-17800 ohms;. At 68°F (20°C), the resistance should be 2200-2700 ohms. At 104°F (40°C), the resistance should be 1000-1300 ohms. At 140°F (60°C), the resistance should be 500-640 ohms. At 176°F (80°C), the resistance should be 280-350 ohms.
    12.  
    13. If all resistances are within specification, go to Step 3. If they are not, go to Step 6.
    14.  
    15. Check ECT sensor voltage as follows:
    16.  

    1. Install the breakout box according to the manufacturers instructions.
    2.  
    3. Place the volt-ohmmeter on the 20 volt scale and turn the ignition key ON .
    4.  
    5. Measure the voltage between pin 7 and pin 46.
    6.  
    7. At 68°F (20°C), the voltage should be 2.5 volts. After warming up, the voltage should be 0.3-0.6 volts.
    8.  
    9. If the voltage readings are within specification, replace the ECA. If they are not, go to Step 4.
    10.  
    11. Check for a short between the ECT sensor and the ECA as follows:
    12.  

    1. Turn the ignition key OFF and disconnect the negative battery cable.
    2.  
    3. Install the breakout box according to the manufacturers instructions.
    4.  
    5. Place the volt-ohmmeter on the 200 ohm scale and measure the resistance between the following pins:

      pin 7 and pin 1
       
      pin 7 and pin 26
       
      pin 7 and pin 37
       
      pin 7 and pin 20
       
      pin 46 and pin 1
       
      pin 46 and pin 26
       
      pin 46 and pin 37
       

    6.  
    7. If any resistances are below 5 ohms, repair the wire(s) in question. If any resistances are not below 5 ohms, go to Step 5.
    8.  
    9. Check the signal return circuit as follows:
    10.  

    1. Turn the ignition key OFF .
    2.  
    3. Install the breakout box according to the manufacturers instructions.
    4.  
    5. Place the volt-ohmmeter on the 200 ohm scale and measure the resistance between pin 46 and pin 20.
    6.  
    7. If the resistance is below 5 ohms, replace the ECA. If the resistance is not below 5 ohms, check the reference voltage and signal return circuits in the sensor harness.
    8.  
    9. Check for an open between the ECT sensor and the ECA as follows:
    10.  

    1. Turn the ignition key OFF .
    2.  
    3. Install the breakout box according to the manufacturers instructions.
    4.  
    5. Place the volt-ohmmeter on the 200 ohm scale and measure the resistance between the ECT sensor yellow/black wire and pin 7 and between the ECT sensor light green/yellow wire and pin 46.
    6.  
    7. If all resistances are below 5 ohms, go to Step 7. If all resistances are not below 5 ohms, repair the wire(s) in question.
    8.  
    9. Check the ECT sensor resistance as follows:
    10.  
    11. Turn the ignition key OFF .
    12.  
    13. Disconnect the ECT sensor.
    14.  
    15. Place the volt-ohmmeter on the 200 ohm scale and measure the resistance across the ECT sensor.
    16.  
    17. At {155}4°F ({155}20°C), the resistance should be 14500-17800 ohms. At 68°F (20°C), the resistance should be 2200-2700 ohms. At 104°F (40°C), the resistance should be 1000-1300 ohms. At 140°F (60°C), the resistance should be 500-640 ohms. At 176°F (80°C), the resistance should be 280-350 ohms.
    18.  
    19. If all resistances are within specification, repair the short in the wire(s). If all resistances are not within specification, replace the ECT sensor.
    20.  



    Click image to see an enlarged view

    Fig. Fig. 3 ECT sensor test schematic 1989 Probe

    1990-92 Vehicles

    1. Check the ECT sensor circuit as follows:
    2.  
    3. Install breakout box tool T83L-50-EEC-IV or equivalent and leave the ECA disconnected.
    4.  
    5. Disconnect the ECT sensor.
    6.  
    7. Using a volt-ohmmeter, measure the continuity between test pin ECT and the ECT circuit terminal at the ECT sensor connector.
    8.  
    9. If there is continuity, go to Step 2. If there is no continuity, repair the ECT wire from the ECA to the ECT sensor.
    10.  
    11. Check the SIGRTN circuit as follows:
    12.  
    13. Install breakout box tool T83L-50-EEC-IV or equivalent and leave the ECA disconnected.
    14.  
    15. Disconnect the ECT sensor.
    16.  
    17. Using a volt-ohmmeter, measure the continuity between test pin SIGRTN and the SIGRTN circuit terminal at the ECT sensor connector.
    18.  
    19. If there is continuity, go to Step 3. If there is no continuity, repair the ECA SIGRTN wire to the ECT sensor.
    20.  
    21. Check ECT sensor resistance as follows:
    22.  
    23. Install breakout box tool T83L-50-EEC-IV or equivalent and leave the ECA connected.
    24.  
    25. Start the engine and bring to normal operating temperature.
    26.  
    27. Measure the resistance between test pins ECT and SIGRTN.
    28.  
    29. If the resistance is between 500-1000 ohms, replace the ECA. If the resistance is not between 500-1000 ohms, replace the ECT sensor.
    30.  



    Click image to see an enlarged view

    Fig. Fig. 4 ECT sensor test pin identification 1990-92 2.2L



    Click image to see an enlarged view

    Fig. Fig. 5 ECT sensor testing data 1990-92 2.2L

    3.0L Engine

    WARNING
    The wire color to test pin 25 is yellow. The wire color to test pin 46 is light green/yellow. The wire color to test pin 7 is yellow/red.

    1. A Code 21 or 116 for the ECT or Code 24 or 114 for the ACT indicates that the corresponding sensor is out of Self-Test range. The correct range of measure is 0.3-3.7 volts. Possible causes are:
    2.  
    3. Low coolant level _ ECT.
    4.  
    5. Ambient temperature below 50°F (10°C) _ ACT.
    6.  
    7. Faulty harness connector.
    8.  
    9. Faulty sensor.
    10.  
    11. Start the engine and run it at 2000 rpm for 2 minutes. If the engine will not start, proceed to Step 5. If the engine stalls, check the idle speed control system.
    12.  
    13. Make sure the upper radiator hose is hot and pressurized, then rerun the Quick Test. If Codes 21, 24, 114 or 116 are present, proceed to Step 4. If they are not, service other codes. as necessary.
    14.  
    15. Check the VREF circuit voltage at the TP sensor as follows:
    16.  

    1. Turn the ignition key OFF .
    2.  
    3. Disconnect the TP sensor.
    4.  
    5. Turn the ignition key ON , but do not start the engine.
    6.  
    7. Using a volt-ohmmeter, measure the voltage between the VREF circuit and the SIG RTN circuit at the TP sensor vehicle harness connector.
    8.  
    9. If the voltage is between 4-6 volts, reconnect the TP sensor and proceed to Step 5. If not, check the vehicle battery power circuit.
    10.  
    11. Check the resistance of the temperature sensor with the engine off as follows:
    12.  
    13. Turn the ignition key OFF .
    14.  
    15. Disconnect the suspect temperature sensor.
    16.  
    17. Measure the resistance between the sensor signal circuit and the SIG RTN circuit at the temperature sensor.
    18.  
    19. If the resistance is within specification, check the ignition system if the suspect sensor is an ECT and the vehicle will not start, otherwise proceed to Step 6. If the resistance is not within specification, replace the sensor and reconnect the vehicle harness. Rerun the Quick Test.
    20.  
    21. Check the resistance of the temperature sensor with the engine running as follows:
    22.  


    WARNING
    The engine may have cooled down. Always warm the engine before taking ECT sensor resistance measurements. Check for an open thermostat.

    1. Turn the ignition key OFF .
    2.  
    3. Disconnect the suspect temperature sensor.
    4.  
    5. Run the engine for 2 minutes at 2000 rpm.
    6.  
    7. Using a volt-ohmmeter, measure the resistance between the sensor signal circuit and the SIG RTN circuit at the temperature sensor.
    8.  
    9. If the resistance is within specification, replace the ECA and reconnect the vehicle harness. Rerun the Quick Test. If the resistance is not within specification, replace the sensor, reconnect the vehicle harness and rerun the Quick Test.
    10.  
    11. A Code 51 or 118 for the ECT or Code 54 or 113 for the ACT indicates that the corresponding sensor signal is greater than the Self-Test maximum. The maximum for ECT and ACT sensors is 4.6 volts. Possible causes are:
    12.  
    13. Open in the wiring harness.
    14.  
    15. Faulty connection.
    16.  
    17. Faulty sensor.
    18.  
    19. Faulty ECA.
    20.  
    21. Attempt to induce opposite Code 61 or 117, or 64 or 112, as follows:
    22.  

    1. Turn the ignition key OFF .
    2.  
    3. Disconnect the suspect temperature sensor.
    4.  
    5. Connect a jumper wire between the sensor signal circuit and SIG RTN circuit at the temperature sensor vehicle harness connector.
    6.  
    7. Run the Key On Engine Off Self-Test.
    8.  
    9. If Code, 61, 64, 112 or 117 is present, replace the sensor, remove the jumper wire and reconnect the vehicle harness. Rerun the Quick Test. If not, remove the jumper wire and proceed to Step 9.
    10.  
    11. Check the continuity of the sensor signal and SIG RTN circuits as follows:
    12.  
    13. Turn the ignition key OFF .
    14.  
    15. Disconnect the suspect temperature sensor.
    16.  
    17. Disconnect the ECA 60 pin connector and inspect for damaged or pushed out pins, corrosion, loose wires, etc. Repair, as necessary.
    18.  
    19. Install breakout box tool T83L-50-EEC-IV or equivalent, and leave the ECA disconnected.
    20.  
    21. Measure the resistance between the sensor signal circuit at the temperature sensor vehicle harness connector and test pin 7 (ECT) or 25 (ACT) at the breakout box.
    22.  
    23. Measure the resistance between the SIG RTN circuit at the temperature sensor vehicle harness connector and test pin 46 at the breakout box.
    24.  
    25. If each resistance is less than 5 ohms, replace the ECA, remove the breakout box, reconnect all components and rerun the Quick Test. If each resistance is not less than 5 ohms, service the open circuits, remove the breakout box, reconnect all components and rerun the Quick Test.
    26.  
    27. A Code 61 or 117 for the ECT or Code 64 or 112 for the ACT indicates that the corresponding sensor's signal is less than the Self-Test minimum. The ACT and ECT sensor minimum is 0.2 volts. Possible causes are:
    28.  
    29. Grounded circuit in harness.
    30.  
    31. Faulty sensor.
    32.  
    33. Faulty ECA.
    34.  
    35. Faulty connection.
    36.  
    37. Attempt to induce opposite Code 51 or 118 or Code 54 or 113 as follows:
    38.  
    39. Turn the ignition key OFF .
    40.  
    41. Disconnect the vehicle harness from the suspect sensor. Inspect for damaged, corroded, pushed out pins or loose wires, etc. Repair as necessary.
    42.  
    43. Run the Key On Engine Off Self-Test.
    44.  
    45. If Code 51, 54, 113 or 118 is present, replace the sensor, reconnect the harness and rerun the Quick Test. If not, proceed to Step 8.
    46.  
    47. Check the VREF circuit voltage at the TP sensor as follows:
    48.  
    49. Turn the ignition key OFF .
    50.  
    51. Disconnect the suspect temperature sensor.
    52.  
    53. Disconnect the TP sensor.
    54.  
    55. Turn the ignition key ON , but do not start the engine.
    56.  
    57. Measure the voltage between the VREF circuit and the SIG RTN circuit at the TP sensor vehicle sensor connector.
    58.  
    59. If the voltage is between 4-6 volts, reconnect the TP sensor and proceed to Step 9. If not, check the vehicle battery power circuit.
    60.  
    61. Check the temperature sensor signal circuit for short to ground as follows:
    62.  
    63. Turn the ignition key OFF .
    64.  
    65. Disconnect the suspect temperature sensor.
    66.  
    67. Disconnect the ECA 60 pin connector and inspect for damaged or pushed out pins, corrosion, loose wires, etc. Repair, as necessary.
    68.  
    69. Install breakout box tool T83L-50-EEC-IV or equivalent, and leave the ECA disconnected.
    70.  
    71. Measure the resistance between test pin 7 (ECT) or 25 (ACT) and test pins 40, 46 and 60 at the breakout box.
    72.  
    73. If each resistance is greater than 10,000 ohms, replace the ECA, remove the breakout box, reconnect all components and rerun the Quick Test. If each resistance is not greater than 10,000 ohms, service the short circuit, remove the breakout box, reconnect all components and rerun the Quick Test.
    74.  
    75. Continuous Memory Codes 51 or 118 (ECT) and 54 or 113 (ACT) indicate that the sensor signal was greater than the Self-Test maximum of 4.6 volts. Continuous Memory Codes 61 or 117 (ECT) and 64 or 112 (ACT) indicate that the sensor signal was less than the Self-Test minimum of 0.2 volts. The code was generated under normal driving conditions. Possible causes are:
    76.  
    77. Faulty sensor.
    78.  
    79. Open circuit in harness.
    80.  
    81. Grounded circuit in harness.
    82.  
    83. Faulty ECA.
    84.  
    85. Check the sensor as follows:
    86.  
    87. Enter the Key On Engine Off continuous monitor mode.
    88.  
    89. Observe the volt-ohmmeter or STAR LED for indication of a fault while tapping on the sensor to simulate road shock.
    90.  
    91. Observe the volt-ohmmeter or STAR LED for indication of a fault while wiggling the sensor connector.
    92.  
    93. If a fault is indicated, disconnect and inspect the connectors. If they are okay, replace the sensor and clear the Continuous Memory. Rerun the Quick Test. If a fault is not indicated, proceed to Step 8.
    94.  
    95. While still in the Key On Engine Off continuous monitor mode, observe the volt-ohmmeter or STAR LED for fault indication while wiggling, shaking or bending small sections of the EEC-IV system vehicle harness from the sensor to the ECA. If a fault is indicated, repair as necessary, clear Continuous Memory and rerun the Quick Test. If a fault is not indicated, proceed to Step 9.
    96.  
    97. Check the ECA and vehicle harness connectors for damage, loose or pushed out pins, loose or poorly crimped wires. Service as necessary.
    98.  
    99. A Continuous Memory Code 338 or 339 indicates a cooling system problem. Check the thermostat, water pump, radiator cap and radiator. Check for low coolant level and check for coolant leaks.
    100.  



    Click image to see an enlarged view

    Fig. Fig. 6 ACT and ECT sensor test schematic 3.0L



    Click image to see an enlarged view

    Fig. Fig. 7 ACT and ECT sensor testing data 3.0L engine

    REMOVAL & INSTALLATION



    For ACT and ECT sensor removal and installation procedures, refer to under Sending Units and Sensors.

     
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