Code 21: Engine Coolant Temperature (ECT) Sensor

NOTE: For component terminal identification, see TERMINAL IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section.

If using scan tester, go to step 2). Remove Engine Coolant Temperature (ECT) sensor from intake manifold. Submerge temperature sensing portion of ECT sensor in hot water. Using DVOM, check resistance across ECT sensor terminals. See ECT SENSOR RESISTANCE SPECIFICATIONS table. If resistance is not as specified, replace ECT sensor. If resistance is as specified, go to step 3).

ECT SENSOR RESISTANCE SPECIFICATIONS

Water Temperature	Approximate Ohms
32°F (0°C)	5800
68°F (20°C)	2400
104°F (40°C)	1100
176°F (80°C)	300

Turn ignition switch to ON or RUN position. Using a thermometer, check engine compartment ambient temperature. Using scan tester, read Engine Coolant Temperature (ECT) sensor voltage. See ECT SENSOR VOLTAGE SPECIFICATIONS table. If voltage is not within specifications, replace ACT sensor. If voltage is within specification, go to next step.

ECT SENSOR VOLTAGE SPECIFICATIONS

Ambient Temperature	Standard Value °F (°C)
-4°F (-20°C)	-20°C
32°F (0°C)	0°C
68°F (20°C)	20°C
104°F (40°C	40°C
176°F (80°C)	80°C

Disconnect ECT sensor connector. Using DVOM, check continuity between chassis ground and connector terminal No. 2. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
Turn ignition switch to ON position. Check voltage between chassis ground and ECT sensor connector terminal No. 2. If voltage is not 4.5-4.9 volts, replace ECM. If voltage is as specified, condition required to set trouble code is not present at this time. Test is complete. Intermittent problem may exist. See TESTS W/O CODES article in the ENGINE PERFORMANCE Section.