Roadmaster 1992

Engine Coolant Temperature Sensor

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Location



Specific to:

Buick Roadmaster 1991-1993

Chevrolet Caprice 1993

Oldsmobile Custom Cruiser 1991-1992



Click image to see an enlarged view

Fig. ECT sensor location-1991-1993

Specific to:

Buick Roadmaster 1991-1993

Chevrolet Caprice 1993

Oldsmobile Custom Cruiser 1991-1992



Click image to see an enlarged view

Fig. ECT sensor location-1991-1993

Operation



Specific to:

Buick Roadmaster 1991-1996

Chevrolet Caprice 1993-1996

Chevrolet Impala 1994-1996

Oldsmobile Custom Cruiser 1991-1992

The Engine Coolant Temperature (ECT) Sensor is a Negative Temperature Coefficient (NTC) Thermistor that monitors the engine coolant temperature. The ECT 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 engine coolant temperature. The PCM uses data from the ECT Sensor to calculate air-fuel mixture, ignition timing, and fuel injector pulse width. In some instances, the ECT signal is used to control the engine cooling fans and the operation of the air conditioning (A/C) system.

Specific to:

Buick Roadmaster 1991-1996

Chevrolet Caprice 1993-1996

Chevrolet Impala 1994-1996

Oldsmobile Custom Cruiser 1991-1992

The Engine Coolant Temperature (ECT) Sensor is a Negative Temperature Coefficient (NTC) Thermistor that monitors the engine coolant temperature. The ECT 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 engine coolant temperature. The PCM uses data from the ECT Sensor to calculate air-fuel mixture, ignition timing, and fuel injector pulse width. In some instances, the ECT signal is used to control the engine cooling fans and the operation of the air conditioning (A/C) system.

Removal & Installation



Specific to:

Buick Roadmaster 1991-1993

Chevrolet Caprice 1993

Oldsmobile Custom Cruiser 1991-1992

At this time the manufacturer does not provide removal and installation procedures for this component. The following procedure is a guideline and may differ from the vehicle you are servicing.

  1. Before servicing the vehicle, refer to the Precautions Section.
    NOTE
    Disconnecting the negative battery cable on some vehicles may interfere with the functions of the on-board computer systems and may require the computer to undergo a relearning process, once the negative battery cable is reconnected.


    NOTE
    If working near and/or around the SRS system and components, be sure to properly disable the SRS system. See disarming/arming the SRS system.

  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Drain the cooling system to an acceptable level. Be sure to properly dispose of used coolant.
  6.  
  7. Remove the air cleaner assembly, as required.
  8.  
  9. Remove the necessary components to gain access to the ECT sensor.
  10.  
  11. Disconnect the electrical connector.
  12.  
  13. Remove the sensor from its mounting.
  14.  
  15. Discard the gasket.

    Click image to see an enlarged view

    Fig. ECT sensor and related components-1991-1993

  16.  

To install:


NOTE
Be sure to use new fasteners, as required.


NOTE
Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread sealer are identified. Do not use paints, lubricants or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners.

  1. Installation is the reverse of the removal procedure.
  2.  
  3. Be sure to use a new gasket.
  4.  
  5. Using the GM diagnostic scan tool or aftermarket equivalent reprogram the necessary systems and components. Be sure to follow the scan tool manufacturer-s directions.
  6.  

Specific to:

Buick Roadmaster 1991-1993

Chevrolet Caprice 1993

Oldsmobile Custom Cruiser 1991-1992

  1. Before servicing the vehicle, refer to the Precautions Section.
    NOTE
    Disconnecting the negative battery cable on some vehicles may interfere with the functions of the on-board computer systems and may require the computer to undergo a relearning process, once the negative battery cable is reconnected.


    NOTE
    If working near and/or around the SRS system and components, be sure to properly disable the SRS system. See disarming/arming the SRS system.

  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Drain the cooling system to an acceptable level. Be sure to properly dispose of used coolant.
  6.  
  7. Disconnect the electrical connector from the coolant temperature sensor.
  8.  
  9. Remove the coolant temperature sensor.
  10.  

To install:


NOTE
Be sure to use new fasteners, as required.


NOTE
Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread sealer are identified. Do not use paints, lubricants or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners.

  1. Install the coolant temperature sensor.
  2.  
  3. Connect the electrical connector.
  4.  
  5. Fill the cooling system.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. Start the engine and check for leaks.
  10.  
  11. Using the GM diagnostic scan tool or aftermarket equivalent reprogram the necessary systems and components. Be sure to follow the scan tool manufacturer-s directions.
  12.  

Testing




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

Connection & Wiring Diagnosis

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.  

ECT Circuit Testing

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

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

Use a suitable pyrometer or thermometer, as well as visual observation to verify that the cooling system is operating properly. If a cooling system fault is evident, repair as required 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 ECT Sensor to verify the signal with a DVOM, and verify PCM communication before replacing the ECT Sensor.

Click image to see an enlarged view

Fig. ECT Sensor Range Chart

ECT Sensor Strategy

The ECT Sensor provides a linear input signal to the Powertrain Control Module (PCM) for a number of engine control system calculations. The ECT signal is compared with Manifold Absolute Pressure (MAP), Mass Air Flow (MAF), Intake Air Temperature (IAT), and Fuel Trim (HO2S) in order to determine the correct air-fuel mixture for measured operating conditions. In some cases the ECT Sensor input is used in concert with the A/C Pressure (ACP) Sensor input in order to determine cooling fan and A/C system operation.

Related Diagnostic Trouble Codes


Click image to see an enlarged view

Fig. Related Diagnostic Trouble Codes

 
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