Question about 1993 GMC Sierra

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Heating System I have a 1993 GMC Sierra 1500 with a 4.3 V6. Problem: the heat gauge on the dash does not show the engine is heating properly, only goes to lowest heat (100 degrees). I've replaced the thermostat (original) but problem still exists. Are there any sensors I could prossibly try replacing? The AC and heat seems to work okay.

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The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold and sends engine temperature information to the ECM. The ECM supplies 5 volts to the coolant temperature sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the ECM monitors a high signal voltage which it interprets as a cold engine. As the sensor warms (internal resistance low), the ECM monitors a low signal voltage which it interprets as warm engine.
Heating System - 0900c1528008f125.jpgFig. 1: View of the Engine Coolant Temperature (ECT) sensor Fig. 2: Engine Coolant Temperature (ECT) sensor locationTESTING
See Figures 3 and 4

  1. Remove the ECT sensor from the vehicle.
  2. Immerse the tip of the sensor in container of water.
  3. Connect a digital ohmmeter to the two terminals of the sensor.
  4. Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the engine coolant sensor temperature vs. resistance illustration.
  5. Repeat the test at two other temperature points, heating or cooling the water as necessary.
  6. If the sensor does not meet specification, it must be replaced.
0900c1528008f120.jpgFig. 3: Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) sensor wiring diagram 0900c1528008f095.jpgFig. 4: ECT sensor temperature vs. resistance values

Posted on Oct 01, 2008

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If the engine seems to run OK, and no Check Engine Light, The sender unit for the gauge (separate sensor) may be bad. On most 4.3L engines, it is located on the driver side rear of the engine. Disconnecting the sender connector (engine warm and Ign. switch in run) should send the gauge to zero, and grounding should send the gauge to 260. If it doesn't, the wiring or gauge could have problems.

Posted on Jun 08, 2009

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