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Engine Coolant Temperature (ECT) Sensor Not Within Limits

  1. Verify that ignition is off. Set test selector switch to position "10". Set DVOM switch to "TESTER". Disconnect ECT connector and connect Blue Test Fixture (203929) to wiring harness. If reading is between 100-250 ohms, go to step  3).
  2. If reading is less than 100 ohms or more than 250 ohms, check Light Green/Yellow wire from ECT sensor to ECA for a short or open. Also check Black/White wire for a short or open. See Figure. Repair wire(s) and retest.
  3. Connect DVOM between pins of ECT sensor connector. Set DVOM switch to "200x1000 OHMS" scale. If reading is more than 6000 ohms, check engine coolant temperature with a thermometer.
  4. If coolant temperature is below 160°F, verify that cooling system is operating in proper temperature range and retest. If coolant temperature is more than 160°F, replace ECT sensor and retest.
  5. If ECT sensor reading in step  3) is less than 1500 ohms, check condition of cooling system, make necessary corrections, and check system operating temperature. If coolant temperature is above 220°F, retest system. If coolant temperature is below 220°F, replace ECT sensor and retest.
  6. If ECT reading in step  3) is between 1500-6000 ohms, replace ECA and retest. After tests, turn test selector switch off and disconnect test equipment. Remove Blue test fixture.
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