TM 9-6115-730-24
0003
ENGINE SENSORS
Boost Pressure
Boost is defined as the difference between the inlet and outlet pressures of the turbocharger. The atmospheric
pressure sensor on the air inlet to the turbocharger is used to reduce smoke emissions at high altitudes and as
the reference for calculating turbocharger boost pressure. Boost pressure measurements are used to reduce
smoke emissions during acceleration. The outlet pressure sensor is located at the turbocharger outlet and
measures pressure from 3 to 49 psi (20 to 340 kPa).
Oil Pressure
The ECM monitors oil pressure following engine start up and may display a low oil pressure alarm diagnostic
code. The code will not be logged for 15 seconds following start up. The output of the oil pressure sensor is pulse
width modulated. The base frequency is 500 150 Hz. The duty cycle varies from 13 to 85% corresponding to 0 to
100 psi (0 to 690 kPa).
Coolant Level Sensor
A sensor in the coolant detects dangerously low levels of coolant in the system. The output of this sensor is
connected to the GSC for display and control.
Crankshaft (bottom or primary) and Camshaft (top or secondary) Engine Speed/Timing Sensors
Two timing sensors determine engine timing. The primary sensor monitors crankshaft rotation and is used to
determine both engine rpm and fuel injection timing. The other sensor senses rotation of the camshaft. With these
redundant sensors, the probability of a failure shutting down the engine is greatly reduced. All of the timing for fuel
injection is based on the output of these sensors. If one fails, timing can continue based on the output of the other
sensor.
Fuel Pressure Sensor
The ECM monitors fuel pressure at the fuel pump between 0 and 100 psi (0 and 690 kPa).
Intake Manifold Air Temperature Sensor
The ECM monitors air manifold inlet temperature and uses this information to adjust ignition timing.
Coolant Temperature Sensor
The coolant temperature is used to determine whether to operate the engine in cold mode and to notify the
operator of excessive engine temperature. If the coolant temperature is below 63F (17C) and the engine is not
in the cranking phase of starting, the timing is advanced and fuel delivery is reduced to improve cold engine
performance. Cold mode remains active until the coolant temperature rises above 63F (17C) or until the engine
has been running five minutes.
0003-2
