Alarms and shutoffs are electronically controlled. The operation of all alarms and shutoffs utilize components which are actuated by a sensing unit. The alarms and shutoffs are set at critical operating temperatures, pressures, or speeds in order to protect the engine from damage.
The alarms function in order to warn the operator when an abnormal operating condition occurs. The shutoffs function in order to shut down the engine when a more critical abnormal operating condition occurs. The shutoffs help to prevent damage to the equipment.
If an engine protective device shuts off the engine, always determine the cause of the shutoff. Make the necessary repairs before attempting to start the engine.
Become familiar with the following information:
- Types of the alarm and shutoff controls
- Locations of the alarm and shutoff controls
- Conditions which cause each control to function
- Resetting procedure that is required before starting the engine
To indicate abnormal operating conditions, the electronic control module provides three outputs for alarm lamps and/or audible alarms. The outputs are for the following conditions:
- Generation of diagnostic codes
- High coolant temperature
- Low oil pressure
The outputs for the alarms are activated for approximately five seconds when power is supplied to the electronic control module. This is a self-test for the alarm circuits.
Generation of Diagnostic Codes
The diagnostic lamp produces a series of flashes that indicate the presence of active diagnostic conditions. The diagnostic lamp can be activated by several conditions. For more information, see this Operation and Maintenance Manual, "Engine Diagnostics" topic (Operation Section).
A coolant temperature sensor measures the temperature of the coolant. An alarm for high coolant temperature is generated under the following conditions:
- The temperature that is measured by the coolant temperature sensor exceeds
104 °C (220 °F) for two seconds. - No diagnostic code is active for the coolant temperature sensor.
An oil pressure sensor measures the oil pressure. The strategy for low engine oil pressure is based on a map of engine oil pressure versus the engine rpm. See Illustration 1.
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| Illustration 1 | g00433181 |
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(Y) Engine oil pressure in kPa
(X) Engine rpm (1) Minimum oil pressure | |
An alarm for low oil pressure is generated under the following conditions:
- The engine rpm is more than 500 rpm.
- A valid signal from the engine oil pressure sensor indicates low pressure for one second.
- No diagnostic codes for the sensor voltage supply are active.
- The engine has been operating for 15 seconds.
The engine will automatically shut down for a low oil pressure condition. The strategy for low engine oil pressure is based on a map of engine oil pressure versus the engine rpm. See Illustration 1.
Engine rpm is detected by magnetic pickups (speed sensors) that are mounted in the flywheel housing. The sensors monitor the engine rpm by sensing the motion of the flywheel ring gear. One sensor is the primary speed sensor, and one sensor is the backup speed sensor.
If a valid signal from the primary speed sensor is not present, a diagnostic code is generated. The secondary speed sensor is then used to detect the engine rpm.
If the engine rpm exceeds the rated rpm by 1.18 times, the engine control module will shut down the engine. The fuel to the engine will be shut off and the air shutoff will activate.
For information on using manual controls for shutting off the engine, see this Operation and Maintenance Manual, "Engine Stopping" topic (Operation Section).