Engine Coolant Temperature - Actron CP9087 Service Manual

Section 2
Typical Engine Coolant
Temperature Sensor
What is It?
How is It
Used?
Location
When to Test
What to
Inspect
2-2
Engine TEMPERATURE
SENSOR
RESISTANCE
The engine temperature sensor is a thermistor - a
resister whose resistance changes with tempera-
ture. The hotter the sensor gets, the lower the
resistance becomes. The thermistor is mounted
inside the tip of a threaded metal housing. This is a
2-wire sensor. (Exception: some Chrysler engines
have a dual sensor with three wires.)
The computer needs to know engine temperature
so it can modify air/fuel ratios, spark advance, idle
speed, and emission device operation (such as an
EGR valve).
The sensor is usually threaded into the engine
block, lower intake manifold, or cylinder head to
provide direct contact with coolant.
• Related trouble codes sent by computer.
• Driveability problems such as hard starting,
rough idle, stalling, hesitation, stumble, surging,
knocking (pinging), poor fuel economy, or black
exhaust smoke.
Sensor operation (see test on page 2-4). Poor
connections at sensor or computer. Faulty sensor
wiring (open or short circuits). Heavy deposits on
sensor tip which can cause poor response.
Leakage into sensor housing. Engine running too
hot (problems with antifreeze, thermostat, water
pump, fan, belts, low engine oil).
HIGH
LOW
Cold
TEMPERATURE
Hot