M318 and M320 Excavators Machine Electronic Control System Caterpillar

Toggle Switch (Automatic Engine Control)

When the operator places the switch for Automatic Engine Control (AEC) in the OFF position, contact "50" of the controller is connected to ground, as if there is a hydraulic demand. The engine RPM is not reduced with hydraulic demand. The AEC switch overrides the following switches: travel/implement pressure switch, swing pressure switch, boom down pressure switch, stick in pressure switch and auxiliary function AEC relay.

Toggle Switch (Power Mode)

When the operator places the power mode switch in the power mode I position, contact "39" of the controller is connected to ground. With the power mode switch in the power mode II position, contact "38" of the controller is connected to ground. The controller determines the contact that the operator has grounded and the controller operates the hydraulics in the corresponding power mode. This will not happen if the input "36" from the travel pedal switch is grounded and contact 37 is not grounded. The controller operates the hydraulics in power mode III under the following condition: Contact "36" from the travel pedal switch is connected to ground and contact "37" of the brake input is not connected to ground.

Toggle Switch (Controller Backup)

When the operator places the backup switch in the MAN position, the solenoids of the proportional reducing valves are disconnected from the controller. This also causes the solenoids of the proportional reducing valves to be connected to the positive terminal of the battery through resistors. This will keep the solenoid valves in a constant position. This will also keep a constant power shift pressure supplied to the hydraulic pump. In the backup mode, the hydraulic pumps will operate at an output that is approximately equal to the output of power mode I.

Note: The controller must be installed in order for the backup switch circuit to operate correctly. The proportional reducing valves do not have a ground without a connection to the controller.

Note: When the switch is in the MAN position, the PDT or PTS would show active fault codes. These active fault codes are Main Pump Circ and Swing Pump Circ. These fault codes appear because the controller is electrically disconnected from the proportional reducing valves.

Toggle Switch (Heavy Lift)

Note: This information is for machines that are equipped with a heavy lift switch.

The Heavy Lift Switch allows the operator to lift very heavy loads with increased control by reducing the speed of the engine. The Heavy Lift Switch also allows the machine to lift heavy loads by increasing the relief setting of the load sensing limiter valve.

Upon selecting Heavy Lift operation, the engine speed will be limited to approximately 1300 RPM. The maximum engine speed is set at the factory. You can re-set the maximum engine speed by using the PDT or PTS with Electronic Technician. Go to the menu "Speed Limit - Heavy Lift". In this menu, you are actually setting the upper limit for the governor actuator request signal from contact 10 and contact 34 of the controller.

Note: Ensure that the engine RPM never exceeds 1300 RPM when the heavy lift function is activated.

Toggle Switch (Travel Lock)

The travel lock switch signals the controller in order to activate the travel lock solenoid.

The controller activates the travel lock solenoid when the following conditions are met:

• The travel pedal is fully depressed. Contact "36" is grounded.

• The travel lock switch is pressed. Contact "35" is grounded.

• The controller input (contact "37") from the brake is open.

The last condition listed above is not met if the input from the brake is connected to ground. This would occur under the following conditions:

• The left console is up.

• The oscillating axle lever is in the brake ON position.

• The brake pedal is depressed

• The parking brake switch is ON.

Limit Switch (Travel Pedal)

Illustration 1	g00545615
Limit Switch (Travel Pedal)

The limit switch for the travel pedal is used to inform the controller that the travel pedal is fully pressed. The limit switch for the travel pedal is used for Power Mode III or for the travel lock control.

Pressure Switch (Travel And Implement: High Pressure)

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Pressure Switch (Travel And Implement)

The travel/implement switch monitors the hydraulic system. The travel/implement switch also informs the controller about the hydraulic demand. The travel/implement switch is not activated under the following conditions:

• When there is no hydraulic demand

• When the pressure in the load sensing line drops below 1475 kPa (214 psi)

If the switch is not activated, contacts 1 and 2 are closed while contacts 1 and 3 are open

The AEC system of the controller uses the travel/implement switch in order to determine the method of operation of the controller.

Pressure Switch (Swing, Boom Down and Stick In: Low Pressure)

Illustration 3	g00540898
Low Pressure Switch (Swing, Boom Down, and Stick In)

The swing pressure switch, the Boom Down pressure switch and the Stick In pressure switch monitor the hydraulic system. The switches also keep the controller aware of the hydraulic demands. When there is no hydraulic demand the pressure switch is open. The AEC system of the controller uses the pressure switch to determine the operation of the controller. The contacts of the swing pressure switch are normally open when the pilot pressure drops below 490 kPa (71 psi). The contacts are also open when the swing pressure switch is off of the machine.

Temperature Switch (Low Hydraulic Oil)

Illustration 4	g00540902
Temperature Switch (Low Hydraulic Oil)

When the hydraulic oil temperature is too low, the low hydraulic oil temperature switch closes. The temperature relay is energized after the low hydraulic oil temperature switch is closed. The temperature relay connects contact "19" of the controller to ground. The output of the hydraulic pump is limited to power mode I when the temperature relay contact is closed to ground. The switch, which is located on the right side of the hydraulic tank, closes at 11 to 14 °C (52 to 57 °F) and opens at 17° ± 2°C (62.6° ± 3.6°F).

Pressure Switch (Brake Light Cutoff)

Illustration 5	g00637827
Brake Light Cutoff Switch (1)

The brake light cutoff switch is located in the left console next to the oscillating axle lever. When the oscillating axle lever is in the brake ON position the brake light cutoff switch closes. This will cause the coil for the stop lamp relay to be energized with 24 VDC. This causes the normally closed contacts of the stop lamp relay to open. The open contacts of the stop lamp relay keep power from reaching the stop lamp from the brake light cutoff switch when the brakes are applied with the oscillating axle lever.

Temperature Switch (High Hydraulic Oil)

Illustration 6	g00540904
Temperature Switch (High Hydraulic Oil)

When the hydraulic oil temperature is too high, the high hydraulic oil temperature switch, which is located on the right side of the hydraulic tank, closes. The temperature relay is energized when the high hydraulic oil temperature switch closes. This causes contact "19" of the controller to be connected to ground. The output of the hydraulic pump is limited to power mode I when the temperature relay contact of the controller is closed to ground. The hydraulic oil temperature switch closes at temperatures above 94° ± 3°C (201° ± 5°F). The switch opens again when the temperature drops below 89° ± 3°C (192° ± 5°F). The high hydraulic oil temperature switch is part of the hydraulic oil temperature sender. These components are in the same part.

Temperature Switch (Engine Coolant)

Illustration 7	g00540907
Temperature Switch (Engine Coolant)

When the engine coolant temperature is too high, the engine coolant temperature switch closes. When the engine coolant temperature switch closes the temperature relay is energized. The temperature relay closes contact "19" of the controller to ground. The output of the hydraulic pump is limited to power mode I when the temperature relay contact of the controller is closed to ground. The engine coolant temperature switch, which is located on the right front side of the engine, closes at temperatures above 100° ± 3°C (212° ± 5°F) and the engine coolant temperature switch opens at temperatures below 95° ± 3°C (203° ± 5°F). The engine coolant temperature switch turns on the indicator for high engine temperature. This switch also sounds an alarm.

Pressure Switch (Forward Travel)

Illustration 8	g00540909
Pressure Switch (Forward Travel)

The travel pressure switch, which is located under the travel pedal, detects forward movement of the machine. The travel pressure switch closes when pilot pressure builds up in the pilot line for forward travel. This causes the travel alarm relay to become energized when the machine is in forward travel operation. This relay activates the travel alarm. The travel pressure switch closes at 517 ± 34.5 kPa (75 ± 5 psi) and opens at 414 ± 34.5 kPa (60 ± 5 psi).

Pressure Switch (Reverse Travel)

Illustration 9	g00540909
Pressure Switch (Reverse Travel)

The travel pressure switch, which is located under the travel pedal, detects reverse movement of the machine. The travel pressure switch closes when the pilot pressure builds up in the pilot line for reverse travel. This causes the travel alarm relay to become energized. This relay activates the travel alarm. The travel pressure switch closes at 517 ± 34.5 kPa (75 ± 5 psi)and opens at 414 ± 34.5 kPa (60 ± 5 psi).

Temperature Sender (Hydraulic Oil)

Illustration 10	g00540904
Temperature Sender (Hydraulic Oil Sender)

The hydraulic oil temperature sender is located in the side of the hydraulic tank. As the hydraulic oil temperature changes, the resistance of the sender changes. As the resistance of the sender changes the hydraulic oil temperature display in the monitor panel changes. The hydraulic oil temperature sender is part of the high hydraulic oil temperature switch. The two components are in the same part.

Temperature Sender (Engine Coolant)

The engine coolant temperature sender is located in the engine cooling system. As the coolant temperature changes, the resistance of the sender changes. As the resistance of the sender changes the engine coolant temperature display in the monitor panel changes.

Fuel Level Sender

The fuel level sender is attached to a float that is located in the fuel tank. As the fuel level changes, the float inside the tank moves. This causes the resistance of the sender to change. As the resistance of the sender changes the fuel level display in the monitor panel changes. The resistance range of the sender is 70.6 ± 2.3 Ohms when the tank is empty and the float is at the bottom of the gauge. The resistance range of the sender is 0.4 ± 2.3 Ohms when the tank is full and the float is at the top of the gauge.