Test De - Engine Coolant Temperature Sensor

To help prevent replacement of good components, check coolant level, oil level, cooling fan operation, thermostat and other related components for proper condition and operation.

1. Engine Coolant Temperature (ECT) Sensor Resistance Check: Turn ignition off and install breakout box. Unplug ECA. Using DVOM on 200-k/ohm scale, measure resistance between Pins No. 7 and 46. Resistances should indicate as shown in ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE  table. If resistance is within specification, proceed to next step. If resistance is not within specification, proceed to step 5).
   ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE
   
   

   Ambient Temperature °F (°C)	Ohms Between TEST Pins No. 7 & 46
   50 (10)	58,750
   65 (18)	40,500
   180 (82)	3600
   220 (104)	1840

2. ECT Sensor Voltage Check: Install breakout box. Using DVOM on 20-volt scale and ignition on, measure voltage between Pins No. 7 and 46. Voltage reading should indicate 2.5 volts at 68°F (20°C). After warming up, voltage reading should indicate 0.3-0.6 volts. If voltage reading is within specification, replace ECA. If voltage reading is not within specification, proceed to next step.
3. Short Between ECT & ECA Check: Turn ignition off and disconnect battery negative terminal. Install breakout box and unplug ECA. Using DVOM on 200-k/ohm scale, measure resistance between the following pins:
   • No. 7 and No. 1.
   • No. 7 and No. 19 (vehicles built before 11/2/87).
   • No. 7 and No. 26 (vehicles built after 11/2/87).
   • No. 7 and No. 37.
   • No. 7 and No. 40.
   • No. 46 and No. 1.
   • No. 46 and No. 19.
   • No. 46 and No. 37.
   If resistances are 10,000 ohms or more, proceed to next step. If resistances are less than 10,000 ohms, repair wire(s) in question.
4. Signal Return Check: Turn ignition off and install breakout box. Using DVOM on 200-ohm scale, measure resistance between pins No. 46 and 40, and pin No. 40 and chassis ground. If resistance is less than 5 ohms, replace ECA. If resistance is 5 ohms or more, repair ground wire.
5. Open Between ECT Sensor & ECA Check: Turn ignition off and install breakout box. Using DVOM on 200-ohm scale, measure resistance between ECT Blue/Red wire and pin No. 7, and ECT Blue/Yellow wire and pin No. 46. If resistance is 5 ohms or greater, repair wire(s) in question. If resistance is less than 5 ohms, proceed to next step.
6. ECT Sensor Resistance Check: Turn ignition off and unplug ECT sensor. Using DVOM on 200-ohm scale, measure resistance across ECT sensor. See ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE  table. If resistance is within specification, repair short in wire(s). If resistance is not within specification, replace ECT.

Fig 1: ECT Sensor Circuit