Test Dr-7A - Testing Engine Coolant Temperature Sensor (Code 21)

NOTE: For connector terminal identification, see CONNECTOR IDENTIFICATION . For appropriate wiring diagram, see WIRING DIAGRAMS at end of article.

Using DRB-II, erase faults. Start engine, and let it idle for more than one minute. Read faults. If Code 21 is displayed again, go to step 3). If Code 21 is not displayed again, read coolant temperature sensor value. While monitoring DRB-II display, wiggle coolant temperature sensor wiring harness.
If coolant sensor value changes, repair wiring harness causing coolant temperature sensor value to change. Perform TEST VER-2. If coolant temperature sensor value does not change, perform TEST DR-14A.
If DRB-II display indicates engine coolant temperature sensor as COOL, allow engine to run until it reaches normal operating temperature. If coolant temperature sensor value is 185-210°F (85-99°C) after engine reaches normal operating temperature, replace Electronic Control Unit (ECU). Perform TEST VER-2.
If coolant temperature sensor value is 313°F (156°C), repair Yellow/Dark Green wire for a short to ground. Perform TEST VER-2. If coolant sensor value is -62°F (-52°C), go to next step. If coolant sensor value is not -62°F (-52°C), replace coolant temperature sensor. Perform TEST VER-2.
Disconnect coolant temperature sensor connector. Turn ignition switch to ON position. Measure voltage between coolant temperature sensor connector terminal No. 2 (Yellow/Dark Green wire) and ground. If voltage is less than 4 volts, go to step 7). If voltage is more than 4 volts, turn ignition switch to OFF position. Measure resistance between coolant temperature sensor connector terminal No. 1 (Dark Green/Black wire) and ground.
If resistance is less than 10 ohms, replace coolant temperature sensor. Perform TEST VER-2. If resistance is more than 10 ohms, repair Dark Green/Black wire for an open circuit to ECU 24-pin connector terminal No. 24. Perform TEST VER-2.
Turn ignition switch to OFF position. Disconnect ECU 24-pin connector. Measure resistance of Yellow/Dark Green wire between ECU 24-pin connector terminal No. 20 and coolant temperature sensor connector terminal No. 2.
If resistance is more than 10 ohms, repair open Yellow/Dark Green wire between ECU and coolant temperature sensor. Perform TEST VER-2. If resistance is less than 10 ohms, replace ECU. Perform TEST VER-2.