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

Coolant Temperature Sensor Schematic:

A faulty coolant temperature sensor will set code 21 in the on-board diagnostic system. Refer to the schematic diagram and test the sensor with the diagnostic chart.

Wire color code identification:

L: Blue
B: Black
Y: Yellow
G: Green
R: Red
W: White
Br: Brown
Lg: Light green
Gr: Gray

Coolant Temperature Sensor Diagnostic Chart:

COOLANT TEMPERATURE SENSOR DIAGNOSTIC CHART


CHECK COOLANT TEMPERATURE SENSOR

With sensor removed from engine, place in water of varying temperatures and measure resistance across terminals. Replace sensor if resistance readings deviate markedly from these ranges:

Water Temp: Resistance:
20° C (68° F) 2-3K Ohms
50° C (122° F) 700-1000 Ohms