Chart A-3, Coolant Sensor Circuit Check
The Coolant Temperature Sensor uses a thermistor to control signal voltage to the ECM. The ECM applies a voltage to the sensor. When the engine is cold, sensor (thermistor) resistance is high, therefore the ECM will see a high signal voltage. As engine warms up, sensor resistance becomes less, and voltage drops. At normal engine operating temperature, voltage will measure about 1-1.5 volts at ECM terminal. Coolant temperature is one of the inputs used to control fuel delivery and air management.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This test checks for faulty coolant sensor or lack of voltage to coolant sensor. Normally there should be .5 volts across coolant sensor connector terminals.
- This test checks coolant sensor resistance. If resistance is under 1000 ohms on a warm engine, coolant sensor is okay. Check for corrosion at connector.