Coolant Temperature Sensor/Switch (For Computer): Testing and Inspection

CIS-E III Control Unit Harness Connectors (Pin # Locations):

CIRCUIT TEST

1. Disconnect harness connector from fuel control unit.

2. Using DVM set to appropriate K-ohms scale, test resistance between harness connector terminal #3 and ground.
- Resistance should be in the range shown in diagram for a given temperature.

Coolant Temperature Sensor Resistance vs. Temperature:

If resistance is higher than specified (or infinite), check for:
a. Poor connections or corroded connector terminals at sensor.
b. Open circuit between fuel control unit terminal #3 and sensor connector terminal #2.
c. Faulty sensor.

If resistance is lower than specified (or zero), check for:
a. Grounded circuit between fuel control unit terminal #3 and sensor.
b. Faulty sensor.

3. Disconnect harness connector from ignition control unit.

4. Using DVM set to appropriate K ohms scale, test resistance between harness connector terminal #25 and ground.
- Resistance should be in the range shown in diagram for a given temperature.

If resistance is higher than specified (or infinite), check for:
a. Poor connections or corroded connector terminals at sensor.
b. Open circuit between ignition control unit terminal #25 and sensor connector terminal #1.
c. Faulty sensor.

If resistance is lower than specified (or zero), check for:
a. Grounded circuit between ignition control unit terminal #25 and sensor.
b. Faulty sensor.



SENSOR TEST

1. Remove sensor from engine and insert rubber plug to prevent coolant loss.

2. Cool sensor by immersing the temperature sensitive end in ice water (the temp. of ice water is approx. 0~C).

3. When sensor is sufficiently cooled, check resistance between each of its terminals and the threaded portion of the housing.
- Resistance should be in the range shown in diagram for 0~C (32~f).

4. Heat sensor by immersing temperature sensitive end in boiling water and recheck resistance (the temp. of boiling water is 100~C/212~F at sea level, slightly less at higher elevations).
- Resistance should be in the range shown in diagram for 100~C (212~f).

If resistance is not within the specified range for BOTH hot and cold tests, replace sensor.