Chrysler Front Wheel Drive Cars 4-CYL 1981-1995 Repair Information

Coolant Temperature Sensor

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OPERATION



Chrysler Electronic Spark Control (ESC) System

The ESC system is used only on 2.2L carbureted engines.

The coolant temperature sensor supplies a signal to the computer indicating the engine temperature. The sensor resistance is inversely related to the temperature of the coolant; therefore, the hotter the coolant, the lower the sensor's resistance. This information is required to prevent changing of the air/fuel ratio until the engine reaches normal operating temperature. It also controls the amount of spark advance during cold engine operation.

Chrysler Mikuni Feedback Carburetor System

The Mikuni feedback carburetor system is used only on 2.6L engines.

The engine coolant temperature sensor installed in the engine coolant passage of the intake manifold is a resistor based sensor. The PCM determines engine warm-up state through the sensor output voltage, and adjusts the air/fuel mixture to provide optimum fuel enrichment.

Chrysler Electronic Fuel Injection (EFI) and Multi-Point Fuel Injection (MFI) Systems

The MFI system is used on 2.2L and 2.5L turbocharged and flex fuel engines.

The coolant temperature sensor is a thermistor (a temperature controlled variable resistor with a range of -40°F (-40°C) to 265°F (129°C) mounted in the engine coolant stream. Engine controller uses the temperature input to adjust the fuel mixture slightly richer and raise the idle speed, until normal operating temperatures are reached. All models equipped with electric cooling fans use this sensor to control the cooling (radiator) fan operation.

Eagle Throttle Body Fuel Injection (TBI) System

The Eagle TBI system is used only on 2.5L Premier engines.

The coolant temperature sensor is installed in the intake manifold coolant jacket. As the coolant temperature varies, the coolant temperature sensor resistance changes resulting in a different input voltage to the PCM Based on this input the PCM will do the following:



Adjust the injector pulse width. Colder coolant temperature will result in longer injector pulse width and richer air/fuel mixtures.
 
Compensate for fuel condensation in the intake manifold.
 
Control the engine warm-up idle speed.
 
Increase the ignition advance when the coolant is cold.
 
Energize the EGR solenoid thus preventing the flow of vacuum to the EGR valve.
 

TESTING



Chrysler Electronic Spark Control (ESC) System
  1. Turn ignition switch OFF and disconnect wire from temperature sensor.
  2.  
  3. Connect one lead of an ohmmeter to one terminal of sensor.
  4.  
  5. Connect other lead of ohmmeter to remaining terminal of sensor.
  6.  
  7. Check for following ohmmeter readings:
    1. Engine at room temperature (approximately 70°F/21°C): Resistance should be 5000-6000 ohms. If not, replace the sensor.
    2.  
    3. Hot engine (normal operating temperature, approximately 200°F/93°C): Resistance should be less than 2500 ohms. If not, replace the sensor.
    4.  

  8.  
  9. If the sensor fails to perform as specified, replace the sensor and retest.
  10.  

Chrysler Mikuni Feedback Carburetor System
  1. Disconnect the negative battery cable.
  2.  
  3. Disengage the electrical connector from the coolant temperature sensor.
  4.  
  5. Connect an ohmmeter to the sensor terminals and measure the resistance as follows:

    With the engine cold, the resistance should be between 3000-17,000 ohms
     
    With the engine warmed up to approximately room temperature, the sensor's resistance should be between 1000-3000 ohms
     
    With the engine warmed up to normal operating temperature, the resistance should be between 100-1000 ohms
     

  6.  
  7. If the resistance deviates from these standard values greatly, replace the sensor and retest.
  8.  

Chrysler Electronic Fuel Injection (EFI) and Multi-Point Fuel Injection (MFI) Systems

See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Engine coolant temperature sensor connector terminal identification



Click image to see an enlarged view

Fig. Fig. 2: Engine coolant temperature sensor circuit schematic for 1988-95 models-earlier models are similar

  1. Disconnect the electrical connector from the coolant temperature sensor.
  2.  
  3. Connect an ohmmeter across the terminals of the sensor. The sensor resistance should be as follows:

    With the engine cold (approximately. 70°F/21°C) the sensor resistance should be between 7,000-13,000 ohms.
     
    With the engine at normal operating temperature (approximately. 200°F/93°C) the sensor resistance should be between 700-1000 ohms.
     

  4.  
  5. If the resistance readings are not within specifications, replace the sensor and retest.
  6.  

Eagle Throttle Body Fuel Injection (TBI) System
  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the coolant sensor electrical connector.
  4.  
  5. Test the resistance of the sensor using a high input impedance ohmmeter. The resistance should be less than 1000 ohms with the engine at normal operating temperature.
  6.  
  7. Replace the sensor if not within the resistance shown in the chart range.
  8.  
  9. If resistance is within specifications, check the resistance of the wiring harness as follows:

    Measure between the PCM connector terminal D3 and the sensor connector terminal.
     
    Measure between the PCM connector terminal C-10 and the sensor connector.
     

  10.  
  11. Repair the wiring harness if the resistance is greater than 1 ohm.
  12.  

REMOVAL & INSTALLATION



See Figures 3 through 6

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Fig. Fig. 3: After disconnecting the battery, detach the sensor wiring connector ...



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Fig. Fig. 4: ... then remove the sensor with a wrench-Chrysler EFI engine



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Fig. Fig. 5: Apply sealant to threads after they are cleaned ...



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Fig. Fig. 6: ... and reinstall the sensor into the water box


WARNING
It is essential that coolant does not contact the accessory drive belt or pulleys because it may cause the belt to slip and/or squeak. Cover the belt and pulleys with shop rags to protect them from coolant spillage. If coolant contacts the belt or pulleys, flush them with clean water.

  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the electrical connector from the coolant temperature sensor.
  4.  
  5. Drain the coolant system until it is below the level of the sensor. Make certain to drain the fluid into a large, clean vessel so that it may be used later.
  6.  
  7. Unscrew the sensor from the thermostat housing or waterbox (next to the thermostat housing).
  8.  

To install:
  1. Start the sensor into its hole slowly, making sure that the threads do not crossthread. Screw the sensor in as far as possible by hand.
  2.  
  3. Tighten the sensor to 21 ft. lbs. (28 Nm).
  4.  
  5. Connect the coolant temperature sensor's electrical plug to the wiring harness.
  6.  
  7. Remove the shop towels from the pulleys and drive belts.
  8.  
  9. Connect the negative battery cable.
  10.  
  11. Refill and bleed the coolant system. For more details, refer to Routine Maintenance .
  12.  
  13. Start the vehicle and check for coolant leaks.
  14.  

 
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