48 ENGINE SYSTEMS
Figure 40 Thermistor
1. Temperature sensor
2. Electronic Control Module (ECM)
3. Microprocessor
4. Voltage Reference (Vref)
5. Ground
Thermistors
•ECT
•EOT
•IAT
•MAT
A thermistor sensor changes its electrical resistance
with changes in temperature. Resistance in the
thermistor decreases as temperature increases, and
increases as temperature decreases. Thermistors
work with a resistor that limits current in the ECM to
form a voltage signal matched with a temperature
value.
The top half of the voltage divider is the current limiting
resistor inside the ECM. A thermistor sensor has two
electrical connectors, signal return and ground. The
output of a thermistor sensor is a nonlinear analog
signal.
Engine Coolant Temperature (ECT)
The ECM monitors the ECT signal and uses this
information for the instrument panel temperature
gauge, coolant compensation, Engine Warning
Protection System (EWPS), and intake heater
operation. The ECT is a backup, if the EOT is
out of range. The ECT sensor is installed in the water
supply housing (Freon® compressor bracket), left of
the flat idler pulley assembly.
Engine Oil Temperature (EOT)
The ECM monitors the EOT signal to control fuel
quantity and timing when operating the engine. The
EOT signal allows the ECM and IDM to compensate
for differences in oil viscosity for temperature
changes. This ensures that power and torque are
available for all operating conditions. The EOT sensor
is installed in the rear of the front cover, outboard of
the high-pressure oil pump assembly.
Intake Air Temperature (IAT)
The ECM monitors the IAT signal to control timing and
fuel rate during cold starts. The IAT sensor is chassis
mounted on the air filter housing.
Manifold Air Temperature (MAT)
The ECM monitors the MAT signal for EGR operation.
The MAT sensor is installed right of the MAP sensor
in the intake manifold.
Figure 41 Variable capacitance sensor
1. Pressure sensor
2. Electronic Control Module (ECM)
3. Ground
4. Microprocessor
5. Voltage reference (V
REF
)
Variable Capacitance Sensors
• BAP
• EBP
•EFP
EGES-265-2
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
Follow all warnings, cautions, and notes.
© 2009 Navistar, Inc.
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