ENGINE COOLANT TEMPERATURE SENSOR—
PCM INPUT
DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is
used to sense engine coolant temperature. The sensor
protrudes into an engine water jacket.
The ECT sensor is a two-wire Negative Thermal
Coefficient (NTC) sensor. Meaning, as engine coolant
temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resis-
tance (voltage) in the sensor increases.
OPERATION
At key-on, the Powertrain Control Module (PCM)
sends out a regulated 5 volt signal to the ECT sensor.
The PCM then monitors the signal as it passes
through the ECT sensor to the sensor ground (sensor
return).
When the engine is cold, the PCM will operate in
Open Loop cycle. It will demand slightly richer air-
fuel mixtures and higher idle speeds. This is done
until normal operating temperatures are reached.
The PCM uses inputs from the ECT sensor for the
following calculations:
• for engine coolant temperature gauge operation
through CCD or PCI (J1850) communications
• Injector pulse-width
• Spark-advance curves
• ASD relay shut-down times
• Idle Air Control (IAC) motor key-on steps
• Pulse-width prime-shot during cranking
• O2 sensor closed loop times
• Purge solenoid on/off times
• EGR solenoid on/off times (if equipped)
• Leak Detection Pump operation (if equipped)
• Radiator fan relay on/off times (if equipped)
• Target idle speed
FIVE VOLT SENSOR SUPPLIES—PRIMARY
AND SECONDARY
DESCRIPTION
Two different Powertrain Control Module (PCM)
five volt supply circuits are used; primary and sec-
ondary.
OPERATION
These 2 circuits will:
• supply the required 5 volt power source to the
Crankshaft Position (CKP) sensor.
• supply the required 5 volt power source to the
Camshaft Position (CMP) sensor.
• supply a reference voltage for the Manifold Abso-
lute Pressure (MAP) sensor.
• supply a reference voltage for the Throttle Posi-
tion Sensor (TPS) sensor.
• supply the required 5 volt power source to the
oil pressure sensor.
• supply the required 5 volt power source for the
Vehicle Speed Sensor (VSS) (if equipped).
• supply the 5 volt power source to the transmis-
sion pressure sensor (if equipped with an RE auto-
matic transmission).
FUEL LEVEL SENSOR—PCM INPUT
DESCRIPTION
The fuel level sensor (fuel gauge sending unit) is
located on the fuel pump module.
OPERATION
Refer to Fuel Gauge Sending Unit in the Fuel
Delivery section for information.
IGNITION CIRCUIT SENSE—PCM INPUT
DESCRIPTION
This circuit ties the ignition switch to the Power-
train Control Module (PCM).
OPERATION
The ignition circuit sense input tells the PCM the
ignition switch has energized the ignition circuit.
Battery voltage is supplied to the PCM through the
ignition switch when the ignition is in the RUN or
START position. This is referred to as the “ignition
sense” circuit and is used to “wake up” the PCM.
Voltage on the ignition input can be as low as 6 volts
and the PCM will still function. Voltage is supplied to
this circuit to power the PCM’s 5 volt primary and 5
volt secondary circuits. This allows the PCM to per-
form fuel, ignition and emissions control functions.
INTAKE MANIFOLD AIR TEMPERATURE
SENSOR—PCM INPUT
DESCRIPTION
The 2–wire Intake Manifold Air Temperature (IAT)
sensor is installed in the intake manifold with the
sensor element extending into the air stream.
The IAT sensor is a two-wire Negative Thermal
Coefficient (NTC) sensor. Meaning, as intake mani-
fold temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resis-
tance (voltage) in the sensor increases.
OPERATION
The IAT sensor provides an input voltage to the
Powertrain Control Module (PCM) indicating the
density of the air entering the intake manifold based
14 - 32 FUEL SYSTEM DN
DESCRIPTION AND OPERATION (Continued)
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