Test Dr-6A - Testing Engine Coolant Temperature Sensor (Code 21)

WARNING: This page is about a different car, the 1994 Plymouth Laser and 1994 Eagle Talon. However, it is still accessible from the selected car via links, so may be relevant.

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

Using DRB, erase faults. Start engine and 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 display, wiggle coolant temperature sensor wiring. Coolant temperature sensor is located on cylinder head, near thermostat housing.
If coolant temperature sensor value changes, repair wiring harness where wiggling caused coolant temperature sensor value to change. Perform TEST VER-2 . If coolant temperature sensor value does not change, perform TEST DR-15A .
Allow engine to run until normal operating temperature is reached. If coolant temperature sensor value is not 185-210°F (85-99°C), go to next step. If coolant temperature sensor value is 185-210°F (85-99°C), replace ECU. Perform TEST VER-2.
If coolant temperature sensor value is not 313°F (156°C), go to next step. If coolant temperature sensor value is 313°F (156°C), repair short to ground in Yellow/Green wire between ECU and coolant temperature sensor. Perform TEST VER-2.
If coolant temperature sensor value is -62°F (-52°C), go to next step. If coolant temperature sensor value is not -62°F (-52°C), replace coolant temperature sensor. Perform TEST VER-2.
Disconnect coolant temperature sensor connector. Turn ignition on. Measure voltage at coolant temperature sensor connector terminal No. 2 (Yellow/Green wire). If voltage is more than 4 volts, go to step 8). If voltage is less than 4 volts, go to next step.
Turn ignition off. Disconnect ECU 24-pin connector. Measure resistance on Yellow/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 circuit in Yellow/Green wire between ECU 24-pin connector and coolant temperature sensor connector. Perform TEST VER-2. If resistance is less than 10 ohms, replace ECU. Perform TEST VER-2 .
Turn ignition off. Measure resistance between coolant temperature sensor connector terminal No. 1 (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 open circuit in Green/Black between coolant temperature sensor and ECU 24-pin connector. Perform TEST VER-2.