GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Engine Coolant Temperature (ECT) Sensor

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OPERATION



See Figure 1

The ECT is mounted usually in the intake manifold or in the coolant stream and sends the engine temperature information to the ECM/PCM. The sensor is a thermistor which changes internal resistance as temperature changes.

The Engine Coolant Temperature (ECT) sensor, sometimes referred to as the Coolant Temperature Sensor (CTS), is a thermistor (resistor which changes value based on temperature) mounted in the engine coolant stream. Low coolant temperatures produce a high resistance-100,000 ohms at 40°F (22°C), while high temperatures cause low resistance-70 ohms at 266°F (130°C).



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Fig. Fig. 1: Engine Coolant Temperature (ECT) sensor and connector

The control module provides a 5 volt reference signal to the sensor through a resistor in the module and measures the voltage. The voltage will be high when the engine is cold and low when the engine is hot. By measuring the voltage, the control module knows the engine coolant temperature. The engine coolant temperature affects most other systems controlled by the module.

Removal and installation of the coolant temperature sensor is covered in Engine & Engine Overhaul of this information.

TESTING



See Figures 2 and 3

Using an ohmmeter, measure the resistance between the terminals. Refer to the appropriate chart for your engine. If the resistance is not as specified, replace the sensor.



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Fig. Fig. 2: Connect the ohmmeter to the ECT sensor terminals to check resistance



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Fig. Fig. 3: Temperature sensor resistance chart

REMOVAL & INSTALLATION



See Figure 4

Be careful when handling the ECT sensor. Damage to the sensor can affect proper operation of the fuel injection system.

  1. Properly relieve cooling system pressure.
  2.  
  3. Make sure ignition is in the OFF position.
  4.  
  5. Disconnect the negative battery cable.
  6.  
  7. For the 1995 3.1L engine, remove the air intake duct.
  8.  
  9. Detach the ECT sensor electrical connector.
  10.  
  11. Carefully back out the sensor.
  12.  



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Fig. Fig. 4: View of the ECT and other sensors

To install:
  1. Coat the threads of the sensor with sealer 9985253 or equivalent.
  2.  
  3. Install sensor into engine, then tighten it to 22 ft. lbs. (30 Nm) for all vehicles except the 1993 3.3L and the 3.1L engines. For the 1993 3.3L engine, tighten the sensor to 18 ft. lbs. (24 Nm). Tighten the sensor to 10 ft. lbs. (14 Nm) on the 3.1L engine. Do NOT strip the threads.
  4.  
  5. Attach the sensor electrical connector.
  6.  
  7. If removed, install the air intake duct.
  8.  
  9. Check coolant level and refill if necessary.
  10.  
  11. Connect the negative battery cable.
  12.  

 
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