953D, 963D and 973D Track-Type Loaders Monitoring System Input Components Caterpillar

The monitoring system receives inputs from the following components.

Senders

953D and 963D Fuel Level Sender

Illustration 1	g01357198
Fuel level sender (1) Sender (2) Schematic symbol

The fuel level sender provides fuel level sensing. A resistive signal from 30 to 245 ohms is sent from the sender to the main display module. This signal corresponds to the depth of fuel within the fuel tank. The machine ECM measures the resistance value in order to determine the fuel that is remaining in the tank. The fuel level sender and the machine ECM are connected at connection J1-30 and connection J1-21. Typical gauge readings for the fuel level:

Table 1

Fuel Level Sender 953D
Real Volume	Resistance	Gauge Reading
11.5%	245.0 Ω	Empty
48%	153.0 Ω	50%
95%	26.0 Ω	Full

Table 2

Fuel Level Sender 963D
Real Volume	Resistance	Gauge Reading
15%	245.0 Ω	Empty
54%	153.0 Ω	50%
96-%	26.0 Ω	Full

973D Fuel Level Sender

Illustration 2	g01918093
Fuel tank with the fuel level sender (3) Fast fill quick disconnect tube (4) Vent (5) Capacitance type fuel level sender

The fuel level sender (5) is mounted to the left side of the fuel tank near the vent. The fuel level sender is a capacitance type sender. A capacitor is formed inside the level sender by a capacitive plate and the aluminum tube of the sender. As fuel is removed from the tanks, the amount of air between the capacitive plate and aluminum tube increases. The resulting capacitance between the plates varies with fuel level and the electronics inside the sender convert the capacitance into one of three different type of signals.

The fuel level sender is an active sender that produces a variable voltage output. The voltage signal is sent to the implement ECM for interpretation. The implement ECM converts the voltage signal from the fuel level sender into a CAN message. The implement ECM then communicates the message to the instrument cluster ECM over the CAN A data link.

The fuel level sender will accurately read the fuel tank level regardless of the type of diesel fuel that is used. Sender accuracy is ensured when diesel fuel, bio-diesels, or eco-diesel fuels are in the tank. However, water in the fuel tank will cause the sender to read improperly. The improper reading is caused by the difference in electrical capacitance of water and diesel fuels.

Table 3

Fuel Level Sender 973D
Output Voltage	Display of the Cat ET	Display of the Instrument Cluster
4.034	100%	100%
2.180	80%	80%
1.405	50%	50%
0.885	25%	25%
0.593	2%	2%
0.545	0	0
A low fuel level warning lamp is illuminated when 12% fuel is remaining in the tank.

Table 3 shows the amount of fuel that is remaining in a percentage. The percentage is based on the output of the fuel level sender in the fuel tank. AVSpare Electronic Technician (Cat ET) will display the amount of fuel that is remaining in the tank as a percentage of a full tank. The "Display of the Instrument Cluster" column of Table 3 indicates the position of the gauge needle as a percentage of needle sweep across the gauge face. An empty tank is indicated on the fuel gauge when the gauge needle is aligned with the left edge of the red arch on the gauge face. When the gauge needle is aligned with the right edge of the right hand green segment on the gauge face the gauge would be indicating that the fuel tank is full.

The voltage output of the sender is not linear with the amount of fuel that is remaining in the tank. The output of the fuel level sender is calibrated in order to indicate a true fuel level at all times. Following are examples of voltage, fuel level, and indication:

• As the level of the fuel drops from the 100% to the 80% indication in Cat ET or on the gauge of the instrument cluster, the voltage output of the sender decreases by 1.854 volts or a change of 46% in the voltage.

• As the fuel level drops from 25% to 2% in Cat ET or on the gauge of the instrument cluster, the voltage output of the sender decreases by .292 volts or 7.3%.

A nonlinear voltage output signal is needed so that the gauge needle does not fall rapidly as the fuel level drops below the two taller sections on each side of the fuel tank. The change in voltage occurs gradually when the fuel level has dropped below the two taller sections of the tank due to the change in the area of the tank.

Temperature Sender (Engine Coolant)

Illustration 3	g01354389
Engine coolant temperature sender

The engine coolant temperature sender is used to operate the water temperature gauge on the instrument cluster. The sender uses variable resistance. The resistance of the sender is proportional to the temperature of the coolant. As temperature increases, the resistance of the sender decreases. The increasing resistance and the decreasing resistance controls the flow of the electrical current in the gauge. The value that is showing on the gauge reflects the amount of current flowing in the circuit. The sender and the gauge are matched to work together as a unit. The engine coolant temperature sender and the engine ECM are connected at connection J2-43 and connection J2-37.

Hydraulic Oil Temperature Sender

Illustration 4	g01354878
Temperature sender (Hydraulic oil)

The hydraulic oil temperature sender senses the temperature of the hydraulic oil. A resistive signal which corresponds to the temperature of the hydraulic oil that is being monitored is sent from the sender to the machine ECM. The resistance of the sender is 34k ohms to 18 ohms. The machine measures the value of the resistance in order to determine the temperature of the fluid. The machine ECM then sends the signal to the temperature gauge on the instrument cluster. The machine ECM uses the hydraulic filter bypass switch and the hydraulic oil temperature sender to determine if the hydraulic oil filter is being bypassed. The filter is being bypassed because the filter is plugged. The temperature sender and the machine ECM are connected at connection J1-22 and connection J2-22.

Sensors

Sensors provide information to the monitoring system about changing conditions. Two of the changing conditions are speed and temperature. The sensor signal changes in a proportional manner in order to reflect the condition. The monitoring system shows the sensor information on the gauges. The recognized sensor signals are listed below.

Frequency - The sensor produces an AC signal with a frequency (Hz) that varies as the condition changes.

Pulse Width Modulated - The sensor produces a digital signal with a duty cycle that varies as the condition changes. The frequency of this signal is constant.

Illustration 5	g00288430
Pulse Width Modulated Signal

Engine Speed Sensor

Illustration 6	g01357699
Magnetic speed pickup (MPU)

The engine speed sensor is a frequency sensor. Speed sensors are used to measure rpm. The sensor generates an AC signal from passing gear teeth, which is sent to the monitoring system. The monitoring system measures the frequency of the sender at a rate of one pulse per gear tooth. The monitoring system then determines the engine speed. Next, the LCD screen on the instrument cluster will show the engine speed.

The magnetic speed pickup (MPU) sends a signal that represents the speed of the engine to the control board and to the tachometer. The MPU is located on the engine flywheel housing. The MPU is a single-pole permanent magnetic generator that is made of wire coils around a permanent magnet pole piece. As the teeth of the flywheel ring gear go through the magnetic lines of flux around the pickup, an AC voltage is generated. A positive voltage is generated when each tooth goes by the pole piece. A negative voltage is generated when each space between the teeth goes by the pole piece. The control board counts the frequency of this speed signal. The control board determines the speed of the engine.

The engine speed sensor and the machine ECM are connected at connection J1-17 and connection J1-18.

Water in Fuel Sensor

Illustration 7	g01918276
Water in fuel sensor (6) Probe (7) Module

The water in fuel sensor is a resistive sensor with a range from 50k ohms to 255k ohms. The sensor receives operating power from the engine ECM at connection J2-18. When the float is at EMPTY, the resistance is approximately 255k ohms. The resistance decreases as the water level in the float increases. The sensor signals the engine ECM. When the ECM measures 50k ohms, the ECM will illuminate the water in fuel indicator on the instrument cluster. The water in fuel sensor and the engine ECM are connected at connection J2-49 and connection J2-40.

Fuel Temperature Sensor

Illustration 8	g01357451
Fuel temperature sensor

The fuel temperature sensor reacts to the temperature of fluids such as engine oil or engine coolant. The sensor receives 5 VDC operating power from the engine ECM at connection J2-46. The temperature sensor sends a signal to the instrument cluster. The signal changes as the temperature of the fuel changes. The engine ECM measures the duty cycle of the sensor signal in order to determine the fuel temperature. The fuel temperature sensor and the engine ECM are connected at connection J2-54 and connection J2-40.

Engine Oil Pressure Sensor

Illustration 9	g01357395
Engine oil pressure sensor

The engine oil pressure sensor is a pressure sensor with a range from 0 kPa to 882 kPa (0 psi to 130 psi). The sensor is an analog sensor that outputs a voltage near 0 volts to 5 volts. The voltage output increases as the pressure increases. The sensor signals the engine ECM. The ground and the signal for the engine oil pressure sensor are connected at connection J2-39 and at connection J2-56 on the engine ECM. The supply voltage for the sensor is connected at connection J2-47 on the engine ECM.

Switches

Switches provide input to the instrument cluster. Switches are two state devices. The two states are described below.

Closed - The switch connects the control input to the ground.

Open - The switch does not connect the control input. The input is floating.

During normal operation, all switches are closed to the ground terminal. When a condition exceeds the trip point of the switch, the switch opens. This tells the instrument cluster of the abnormal condition. The instrument cluster goes into warning operation. The instrument cluster notifies the operator of the abnormal condition.

Note: See Engine Service Manual, "Electrical System Schematic" for specifications for switches.

Switches for Lift Kickout, Tilt Kickout and Float Positions

Illustration 10	g01360284
Joystick control

Illustration 11	g01360965
View A-A and schematic

Illustration 12	g01360967
View B-B and schematic

Illustration 13	g01361095
Single axis lever

The bucket may be controlled by one of the following ways:

• A joystick control

• Two single axis levers

Both types of controls have a detent position. The detent will release when a particular kickout position is reached. The proper LED indicator will illuminate on the instrument cluster when a kickout position is reached.

Lift Kickout

The lift kickout switch is a magnetic switch that is mounted on the lift arm linkage of the machine. When the lift arm linkage reaches a specific preset height, the lift kickout switch will sense the position and the lift control lever will automatically be returned to the HOLD position.

Tilt Kickout

The tilt kickout switch is a magnetic switch that is mounted on the bucket tilt linkage of the machine. When the bucket tilt linkage reaches a specific preset position, the tilt kickout switch will sense the position and the tilt control lever will automatically be returned to the HOLD position.

Note: The parameters of the kickouts can be set by the operator with a rocker switch that is located in the operator station.

Note: The detent is a magnetic coil in the pilot control valve.

Fuel Filter Plugged Switch

Illustration 14	g01355938
Fuel filter bypass switch (differential pressure switch)

The fuel filter differential pressure switch is used to detect excessive restriction in the fuel filter. The switch is normally closed. When the fuel pressure at the switch reaches an actuation pressure the switch will open. The switch is used in order to detect a plugged fuel filter element. The engine ECM will illuminate the plugged fuel filter indicator on the instrument cluster during this condition. The Messenger will display "Secondary Fuel Filter Plugged".

The differential pressure switch and the engine ECM are connected at connection J2-41 and connection J2-38.

Fuel Pressure Switch

Illustration 15	g01455347
Fuel pressure switch

The switch is used in order to monitor the fuel pressure in the system. This switch is normally closed. The Fuel Pressure Switch is located just after the Primary fuel filter. When the switch detects low pressure, the switch opens and the indicator will be illuminated on the instrument cluster. The Messenger will display "Primary Fuel Filter Plugged".

The switch signals the engine ECM. The ground and the signal for the fuel pressure switch are connected at connection J2-36 and at connection J2-38 on the engine ECM.

Switch for the Hydraulic Oil Filter Bypass

Illustration 16	g01918280
Switch for the hydraulic oil filter bypass

If the element in the hydraulic oil filter housing becomes full of debris, the restriction to the flow of oil causes a pressure increase inside the housing. When the pressurized oil activates the bypass switch, the hydraulic oil filter bypass indicator will be illuminated on the instrument cluster.

The switch for the hydraulic oil filter bypass is activated when the hydraulic filter is being bypassed. The switch is a pressure switch that is activated when the pressure reaches 276 ± 28 kPa (40 ± 4 psi). The switch deactivates at 179 kPa (26 psi). The switch signals the machine ECM at connector J2-61.

The machine ECM reads the switch status of the hydraulic oil filter bypass and the hydraulic oil temperature. The switch status of the hydraulic oil filter bypass and the hydraulic oil temperature will be used to determine if the hydraulic oil filter is plugged.

Air Inlet Restriction Switch

Illustration 17	g01353907
Air inlet restriction switch

The air inlet restriction switch is an input of the monitoring system. This pressure switch senses the inlet pressure. The air inlet restriction switch is a normally open switch. The trip point for the switch is at 7.5 kPa (30 inch of H₂O). The circuit in the switch will close at the trip point. The closed switch will send a signal in order to illuminate the air inlet restriction indicator on the instrument cluster. The air inlet restriction switch and the engine ECM are connected at connection J1-38 and connection J1-35.

Ether Aid Solenoid

Illustration 18	g01353966
Ether aid solenoid

During cold weather, the engine ECM will automatically determine when the premeasured amount of ether is injected into the engine air intake. The indicator on the instrument cluster will illuminate when the solenoid for the ether aid is activated. Also, the operator can manually activate the ether aid solenoid with a rocker switch in the operator station. The ether aid solenoid and the engine ECM are connected at connector J1-29 and connector J1-25.

Inputs for the Operator Present Status

The operator present status determines when it is permissible for the operator to enable the hystat transmission and the implement system. The operator present status is determined by the following four inputs:

• The tilting armrest switch

• The operator present switch (Seat switch)

• The brake pedal position sensor

• The motor speeds for the left track or the right track

The following conditions indicate that the operator is NOT PRESENT:

• The armrest is raised up.

or

• The armrest is fully down.

• The seat switch is open.

• The brake pedal travel is less than 10 percent.

• The speeds of the track motor are zero.

The following conditions indicate that the operator is PRESENT:

• The armrest is fully down.

• The operator present switch is closed.

• The brake pedal travel is greater than 10 percent.

• The speeds of the track motors are not zero.

Tilting Armrest Switch

Illustration 19	g01354106
Tilting armrest switch

The tilting armrest switch works with three other inputs in order to determine the operator present status. The tilting armrest switch and the machine ECM are connected at connector J1-42 and connector J1-43.

Operator Present Switch

Illustration 20	g01354324
Operator present switch

The operator present switch is located under the operator seat. The operator present switch works with three other inputs in order to determine the operator present status.

The switch is normally open. The operator present switch supplies two switch to ground inputs to the engine ECM and to the machine ECM. At that time, the machine ECM will not allow the following actions:

• The machine to shift out of NEUTRAL

• Disengagement of the parking brake

• Enable the engine start sequence.

The operator present switch and the machine ECM are connected at connector J2-30 and connector J2-31.

Brake Pedal Position Sensor

Illustration 21	g01362378

The service brake pedal position sensor works in conjunction with three other inputs in order to determine the operator present status. The brake pedal position sensor is a PWM sensor with a PWM output. The position sensor is a input signal to the machine ECM. The sensor is designed to determine the position of the service brake pedal.

If the service brake pedal is engaged more than 10 percent of the total brake pedal travel, the brake pedal position sensor tells the monitoring system that an operator is present.

The brake pedal position sensor receives 8 VDC on contact J1-44 of the machine ECM. The service brake pedal position sensor is grounded on connector J1-45 of the machine ECM. The signal circuit of the service brake pedal position sensor connects to connector J2-27 of the machine ECM.

Right Track Speed Sensor and Left Track Speed Sensor

Illustration 22	g01362270

The two track speed sensors work in conjunction with three other inputs in order to determine the operator present status.

The left track speed sensor and the right track speed sensor are located on the respective final drives. The track speed sensors transmit the speed and the direction of the tracks to the machine ECM by sensing the sprocket in drive motors.

The speed sensors for the tracks are an input of the machine ECM. The sensor tells the ECM the speed of each track. The speed sensors for the tracks are frequency sensors. Frequency sensors produce a signal that varies the frequency as the condition changes.

Key Start Switch

Illustration 23	g01333401
Key start switch

When the key start switch is in the ON position, electrical power from the batteries is supplied to the electronic control modules.

When the key start switch is in the START position and the conditions for starting the engine are satisfied, the start relay is energized.

Parking Brake Switch

Illustration 24	g01356599
Parking brake switch

The parking brake switch is a two pole double throw rocker switch. The ON/OFF pole of the parking brake switch is an input of the machine ECM. The ON/OFF pole informs the ECM that the operator wants the parking brake engaged. The ECM shifts the transmission to NEUTRAL and the ECM de-energizes the brake solenoid valve to the left and right brakes. The solenoid valve redirects the hydraulic oil pressure that keeps the brakes disengaged. Without hydraulic oil pressure, the brakes will engage. The brakes are applied with a mechanical spring. The brakes are hydraulically released. When you de-energize the brake solenoid valve, hydraulic pressure is removed from the brakes and the brakes are locked by mechanical force.

The ON/OFF pole has two input connections to the machine ECM. The normally closed contact of the parking brake switch is at connector J1-33. The normally open contact of the parking brake switch is at connector J1-34. When the operator places the parking brake switch in the ON position, the normally closed circuit is open and the normally open circuit is closed to ground. When the switch is in the OFF position, the normally closed circuit is closed to ground and the normally open circuit is open.

Implement Lockout Switch

Illustration 25	g01356609
Implement lockout switch

The implement lockout switch is used to deactivate the pilot oil supply of the implement system. The implement lockout solenoid is de-energized when the operator places the implement lockout switch in the LOCKED position. This solenoid valve blocks supply oil to the implement main control valve. No pilot pressure will be available for initiating movement of the bucket or the ripper.

The implement lockout switch and the machine ECM are connected at connector J2-46 and connector J2-47. The implement lockout solenoid is activated and deactivated from connector J2-2 and connector J2-4 on the machine ECM.

Reversing Fan Switch

Illustration 26	g01242277
Reversing fan switch

The reversing fan switch is located on the right hand console. The reversing fan switch will energize the reversing fan solenoid. The reversing fan solenoid redirects hydraulic pressure in order to reverse the cooling fan. When the reversing fan switch is in the OFF position the following actions will occur:

• On 20 minute intervals, the engine cooling fan will automatically reverse. The fan will run in reverse for 20 seconds before the fan returns to forward motion.

• If you press the switch momentarily, the cooling fan will reverse for 20 seconds before returning to forward motion.

• The purge interval and the duration of the purge are configurable with Electronic Technician (ET) or the Messenger. The purge interval can be configured from 300 seconds to 7200 seconds. The duration of the purge can be configured from 5 seconds to 30 seconds.

The reversing fan switch and the machine ECM are connected at connector J1-63 and connector J1-64.

MSS Key Reader Control

The AVSpare machine security system (MSS) serves the following purposes:

• Prevent unwanted machine operation.

• Prevent theft of the machine.

• Prevent unauthorized operation of the machine.

Components of the MSS

The MSS consists of the following components:

• Machine ECM

• Electronic key

• Exciter coil

• Key reader

• Status indicator

Basic Operation

Note: Ensure that you have only one electronic key near the exciter coil when the MSS reads the key. If there is more than one key the ECM will not be able to read the key and the machine will not start.

MSS may be programmed to read a standard AVSpare key or an electronic key. The electronic key contains an electronic chip within the plastic housing for the key. Each key emits a unique signal to the MSS. The keys can be identified by a gray housing or a yellow housing. MSS can have programmed settings to require an electronic key or a standard AVSpare key for starting during certain periods of time.

The electronic control module (ECM) of the MSS is setup with the ID of the keys of the intended users. When the MSS is armed, the ECM validates the ID of the key in the key start switch. If the ID for the key is in the list of authorized keys in the ECM and the key is valid, the machine will operate normally. If the ID for the key is not in the list of authorized keys in the ECM or the key is not valid in the ECM, the MSS will keep the critical machine functions disabled. The following table tells the operator the status for starting the machine. The status light is located near the key start switch.

Table 4

MSS Status Light
Red light	The key is not authorized.

Note: MSS will not shut down the machine after the machine has started.

Switches (Buttons) of the Messenger Display

Illustration 27	g01918282
Switches (Buttons) of the Messenger (8) Back Button (9) Left/Up Button (10) Right/Down Button (11) OK Button

Back Button - This button is used in order to return to the previous screen.

Left/Up Button - This button is used for navigation of the menu and to set data.

Right/Down Button - This button is used for navigation of the menu and to set data.

OK Button - This button is used to confirm a selection on the screen.

See the System Operation, "Menu Navigation" Section of this manual for details.