Chart A-3 Coolant Sensor Circuit Check

Fig. 036 - Wiring Diagram for Chart A-3 Coolant Sensor Circuit Check. VIN C:

CHART A-3, COOLANT SENSOR CIRCUIT CHECK

The Coolant Temperature Sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see a high signal voltage.
As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature the voltage will measure about 1 to 1.5 volts at the ECM terminal.
Coolant temperature is one of the inputs used to control:
a. Fuel delivery.
b. Air Management (A.I.R.)

Fig. 035 - Chart A-3 Coolant Sensor Circuit Check.:

1. Checks to see if the fault is the coolant sensor or lack of voltage to the coolant sensor.
Normally there should be about .5 volts across the coolant sensor connector terminals.
2. Checks resistance of the coolant sensor.
If the resistance is under 1000 ohms on a warm engine, the coolant sensor is not faulty. Therefore, check for corrosion at the connector.