3176B Marine Engine Caterpillar

Sensor Locations

Illustration 1, Illustration 2, Illustration 3, and Illustration 4 show the typical locations of the sensors for a 3176B Marine Engine. Specific engines may appear different from the illustrations due to differences in applications.

Illustration 1	g00579598
Front view of engine (1) Coolant temperature sensor (2) Speed/timing sensor (3) Backup speed/timing sensor

Illustration 2	g00579639
Right side view of engine (4) Oil pressure sensor

Illustration 3	g00579766
Left side view of engine (5) Coolant level sensor (6) Fuel temperature sensor (7) Fuel pressure sensor

Illustration 4	g00579601
Top view of engine (8) Inlet manifold air temperature sensor (9) Inlet manifold air pressure sensor

Failure of Sensors

All Sensors

A failure of any of the sensors may be caused by one of the following malfunctions:

• Sensor output is open.

• Sensor output is shorted to "- battery" or "+ battery".

• Measured reading of the sensor is out of specification.

Atmospheric Pressure Sensor

Atmospheric pressure sensor (6) measures the atmospheric pressure in the crankcase. A signal is sent to the Electronic Control Module (ECM).

Coolant Temperature Sensor

Coolant temperature sensor (1) monitors engine coolant temperature. This feature is used for engine system diagnostics with an output from the ECM. The output of the ECM can indicate a high coolant temperature through a relay or a lamp. In addition, the sensor activates the cold start strategy which improves the startability of the engine.

Failure of the Coolant Temperature Sensor

If one of the following conditions exist, a failure of the coolant temperature sensor may have occurred:

• Sensor output is open.

• Sensor output is shorted to ground or supply.

• Measured reading of the coolant temperature is out of specification.

The ECM will detect a failure of the coolant temperature sensor. The diagnostic lamp will warn the operator about the status of the coolant temperature sensor. Coolant temperature related strategies will be disabled if a failure occurs. A failure of the coolant temperature sensor will not cause a shutdown of the engine or any horsepower change.

Coolant Level Sensor

Note: Coolant level sensor (5) is an optional feature.

Coolant level sensor (5) monitors the level of the engine coolant. The coolant level sensor is used to detect a condition when the coolant level is low. The coolant level sensor provides information to the ECM. The output from the ECM can indicate low coolant level through a relay or a lamp. Coolant must be added to the cooling system in order to correct the condition.

The system can be programmed with one of the following options:

ENABLED - The system will monitor the input from the coolant level sensor. The system is programmed with this value when the engine is shipped by Caterpillar.

DISABLED - The system will not monitor the input from the coolant level sensor. All of the diagnostics that are associated with the coolant level sensor will be disabled.

Failure of the Coolant Level Sensor

A failure of the coolant level sensor may occur under the following conditions:

• The coolant level sensor is open.

• The coolant level sensor is shorted to ground.

• The coolant level sensor is shorted to supply.

The failure of the coolant level sensor will not cause a shutdown of the engine or any horsepower change.

Engine Oil Pressure Sensor

The engine oil pressure sensor (4) is mounted in the front of the cylinder block. The oil pressure sensor senses oil pressure at the bearing oil gallery.

Note: The oil pressure switch may close at 48 to 62 kPa (7 to 9 psi) below the actual trip point.

Low Oil Pressure Warning

The setpoint is dependent upon the engine speed. The fault will be active and logged only if the engine has been running for more than 15 seconds.

Very Low Oil Pressure Warning

The very low oil pressure setpoint is dependent upon the engine speed. If the DERATE mode of the engine monitoring system is selected, the ECM will derate the engine power. The engine horsepower will be limited.

Failure of the Engine Oil Pressure Sensor

The ECM will detect failure of the engine oil pressure sensor. The diagnostic lamp warns the user about the status of the engine oil pressure sensor. The engine oil pressure related strategies will be disabled in the event of a failure of the engine oil pressure sensor. A failure of the engine oil pressure sensor will not cause a shutdown of the engine or any horsepower change.

Engine Speed/Timing Sensor

If the ECM can not receive a signal from the primary speed/timing sensor (8), the "DIAGNOSTIC" lamp will indicate a diagnostic fault code which will be logged in the ECM memory.

The backup speed/timing sensor (9) is used when the ECM does not receive a signal from the primary speed/timing sensor (8). The backup speed/timing sensor will be used until the primary speed/timing sensor is replaced.

Failure of the Speed/Timing Sensor

A failure of the speed/timing sensor may have occurred if one of the following conditions occur:

• The output of the speed/timing sensor has opened.

• The speed/timing sensor is shorted to ground.

• The speed/timing sensor is shorted to supply.

• The speed/timing sensor is missing pulses.

• The speed/timing sensor has extra pulses.

Intermittent failure causes erratic engine control. The ECM will detect a failure of the primary speed/timing sensor. The operator will be warned through the diagnostic lamp.

Fuel Pressure Sensor

Fuel pressure sensor (7) monitors the fuel filter outlet pressure. Low fuel pressure or high fuel pressure will not cause a shutdown of the engine or any horsepower change. Fuel pressure that is outside of the normal range will affect the engine performance. If the fuel filter outlet pressure is low, the fuel filter may need to be replaced.

Fuel Temperature Sensor

Fuel temperature sensor (6) monitors the fuel temperature. Fuel temperature is monitored in order to adjust the fuel rate so that the engine will deliver consistent power. The fuel temperature sensor can also be used to warn the operator of excessive fuel temperature. A high fuel temperature can adversely affect the engine performance.

Inlet Manifold Air Temperature Sensor

The inlet manifold air temperature sensor (8) measures the inlet manifold air temperature. The Electronic Control Module (ECM) monitors the signal from the inlet manifold air temperature sensor. The output of the ECM can indicate high inlet manifold air temperature through a relay or a lamp. The inlet manifold air temperature sensor will not cause a shutdown of the engine or any horsepower change.

Note: The inlet manifold air temperature sensor will be affected by the heat that is conducted from the inlet manifold. This is true when the engine is idling and after the engine is shut off. This warm-up is due to the lack of coolant circulation through the engine. The reading from the inlet manifold air temperature sensor may be significantly higher than the actual temperature of the air inside the inlet manifold until the inlet manifold cools.

Inlet Manifold Air Pressure Sensor

The air/fuel ratio control utilizes actual engine speed and actual boost pressure (inlet manifold air pressure) in order to control the transient smoke level. When the throttle is increased and when the engine demands more fuel, the fuel limit is controlled in order to reduce overall smoke levels of the engine exhaust.

The Electronic Control Module (ECM) controls injection timing and the amount of fuel that is injected.

Note: The inlet manifold air pressure sensor (9) is located on the top right side of the engine. The sensor is located in front of the inlet manifold air temperature sensor.

The boost pressure is determined from the difference in pressure between the inlet manifold air pressure sensor and the atmospheric pressure sensor (crankcase pressure).

Failure of the Inlet Manifold Air Pressure Sensor

A failure of the inlet manifold air pressure sensor may have occurred if any of the following conditions are present:

• The output of the inlet manifold air pressure sensor is open.

• The output of the inlet manifold air pressure sensor is shorted to ground or to supply.

• The reading of the inlet manifold air pressure sensor is out of specification.

The ECM will detect the failure of the inlet manifold air pressure sensor. The operator will be warned of the problem through the diagnostic lamp. The strategies that are related to the boost will be disabled. The inlet manifold air pressure sensor failure will not cause a shutdown of the engine or any horsepower change.

Marine Transmission Oil Pressure

Monitoring the transmission oil pressure is a programmable option. The Electronic Control Module (ECM) monitors transmission oil pressure with a sensor. The sensor is located on the high pressure side of the transmission. High transmission oil pressure is detected for diagnostics, similar to the monitoring of the engine oil pressure.

The output from the ECM monitors the transmission oil pressure. The maximum allowable transmission oil pressure is 700 to 2963 kPa (102 to 430 psi). The output of the ECM can indicate high oil pressure through a relay or a lamp.

Marine Transmission Oil Temperature

The transmission oil temperature sensor measures the temperature of the transmission oil. The Electronic Control Module (ECM) uses this information to diagnose a problem. The information is also used to warn the operator of excessive transmission temperature.

The output from the ECM monitors the transmission oil pressure. The maximum allowable transmission oil temperature is 50 to 120°C (122 to 248°F). The output of the ECM can indicate high transmission oil temperature through a relay or a lamp.