ENGINE SENSORS - Continued
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.
Primary and Backup Engine Speed/Timing Sensors
Two speed/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 in the same manner as
the first. 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 the primary sensor fails, timing can
continue based on the output of the backup sensor.
Fuel Pressure Sensor
The ECM monitors fuel pressure at the fuel pump between 0 and 100 psi (0 and 690 kPa).
Inlet Air Manifold 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.
The speed input signal to the ECM is a pulse width modulated control signal, which eliminates the mechanical
throttle and governor linkages along with their adjustments. The nominal frequency is 500 200 Hz. The pulse
width varies from 10% to 90% corresponding to idle and maximum speed of the engine. Signals outside of this
range are considered a failure and a fault code is logged.