HOLDEN GEN III V8, Service Training

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GEN III V8 ENGINE MANAGEMENT
ENGINE COOLANT TEMPERATURE SENSOR
The Engine Coolant Temperature (ECT) sensor is
a thermistor, (a resistor that changes value based
on temperature) mounted in the engine coolant
stream. Low engine coolant temperature produces
a high sensor resistance (29k ohms at -20°C) while
high engine coolant temperature causes low
sensor resistance (180 ohms at 100°C).
The PCM supplies a 5 volt signal voltage to the
sensor through a resistor network in the PCM, and
monitors the circuit voltage, which will change
when connected to the sensor.
The circuit voltage will vary depending on the
resistance of the coolant temperature sensor. The
circuit voltage will be close to the 5 volt level when
the sensor is cold, and will decrease as the sensor
warms. Engine coolant temperature affects most
systems controlled by the PCM.
The PCM uses a dual pull up resistor network to
increase the resolution through the entire operating
range of engine coolant temperature. When the
coolant temperature is less than 51 °C both the 4K
and 348 ohm resistors are used. When the coolant
temperature reaches 51 °C. The PCM switches a
short across the 4K resistor and only the 348 ohm
resistor is used.
As the engine warms, the sensor resistance
becomes less and the voltage at the PCM coolant
temperature sensor signal terminal should
decrease from approximately 4.5 volts when cold
to 0.9 volts at 51 °C. At this temperature the PCM
switches the short across the 4k resistor, the
voltage will then rise to 3.5 volts. The voltage will
again decrease as the coolant temperature
increases until at normal engine operating
temperature (95°C), the voltage should be less
than 2.0 volts.
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