994K Wheel Loader Machine Systems Caterpillar

Electronic Control Module (ECM)

Illustration 1	g03881193

Illustration 2	g03094428
(1) Connector view from ECM side (2) Connector view from harness side

The ECM decides based on input information and memory information. After the ECM receives the input information, the ECM sends a corresponding response to the outputs. The inputs and outputs of the ECM are connected to the machine harness by two 70 contact connectors (J1 and J2). The inputs and outputs to the ECM can be viewed through the Cat^® Electronic Technician (Cat ET) Service Tool.

This machine is equipped with multiple electronic control modules. The brake system uses the implement ECM and the transmission ECM.

Note: Only the complete ECM is serviced (no lower levels components). The ECM must be replaced if the ECM is damaged. Replace the ECM if a failure is diagnosed.

Pin Locations

Illustration 3	g03887268

Illustration 4	g03890049

Inputs

The inputs describe the status of the machine systems. Two types of inputs exist. The inputs can be either a switch type or a sensor type. Switches provide an open, a ground, or a + battery signal to the inputs of the controller. Sensors (frequency, pulse width modulated (PWM), or voltage) provide a changing signal to the sensor inputs of the controller. The inputs to ECMs are listed in table.

Temperature Sensors

Front/Rear Axle Oil Temperature Sensor

Illustration 5	g03877882

The axle oil temperature sensor sends a PMW signal to the Implement ECM indicating axle oil temperature. The duty cycle range for this sensor is 10.01% at −40° C (−40° F) to 89.26% at 120° C (248° F).

The Brake System uses one temperature sensor for the front axle oil and one temperature sensor for the rear axle oil.

Pressure Sensors

Brake Accumulator Pressure Sensor, Park Brake Oil Pressure Sensor, and Front/Rear Service Brake Pressure Sensor

Illustration 6	g03877924

The brake pressure sensor informs the XMSN ECM of brake system pressure. The pressure sensor output is a pulse width modulated signal. The duty cycle of the signals will vary in proportion to the system pressure. These PWM signals are inputs to the XMSN ECM. The XMSN ECM provides 8 V supply and 8 V return for the sensor.

The Brake System uses one pressure sensor for the front axle and one pressure sensor for the rear axle.

Switches

Switches provide one of the following types of input to the ECMs.

• Open

• Ground (-)

• Battery (+)

Switches are devises that have two states, Open and Closed.

• When a switch is open, no signal is provided to the corresponding input of the ECM. This condition is also referred to as floating.

• When a switch is closed, a ground signal (-) or a battery signal (+) is provided to the corresponding input of the ECM.

Parking Brake Solenoid

Illustration 7	g03887161

The parking brake solenoid is an on/off type solenoid that controls the flow of oil the parking brakes. The ECM sends a signal to energize or de-energize the solenoid depending on operator request. When the solenoid is energized, hydraulic oil is allowed to flow to the parking brakes, dis-engaging the parking brakes.

Parking Brake Operator Switch

Illustration 8	g03431151

The parking brake operator switch is a two pole switch. The switch has a common return for both poles of the switch, and three ECM contacts. Two of the contacts are on one pole and are a normally open and a normally closed contact. In the normally operating position, the normally open contact floats to a high voltage state and the normally closed contact is pulled to a low voltage state. The last ECM contact is an additional normally closed contact. When the switch is activated the normally closed contacts float to a high voltage state, and the normally open contact is pulled to a low voltage state. By monitoring the voltage state of the three ECM contacts, the ECM is able to determine the operator request for parking brake.

Front/Rear Brake Lube Oil Pressure Switch

Illustration 9	g03877962

The brake lube oil pressure switch is a pressure switch that is used by the XMSN ECM to monitor the brake lube oil pressure. The pressure switch is a normally open switch. When the proper pressure is supplied to the switch, the switch will send a ground (-) signal to the XMSN ECM. There is one switch for the front axle and one switch for the rear axle.

RH Brake Pedal Switch

Illustration 10	g03882473

The RH brake pedal has a two pole limit switch. The pedal changes the state of the switch when it is pressed. The first pole controls the brake lights and is directly connected to the switch. The contact for the light is normally open and is closed when the switch is depressed. The second pole alerts the ECM to the state of the brake pedal. The contact for the ECM is normally closed and opens when the pedal is depressed.

Outputs

The ECMs respond to decisions by sending electrical signals to the outputs. The outputs can create an action or the outputs can provide information to the operator or the service technician. The outputs of the ECM are listed in tables .

Data Link

Cat Data Link

The Cat Data Link is an input/output of the ECM. The data link uses the connector for the service port in order to communicate with the Cat ET. A data link connection is provided for the product link.

Note: The control for the product link provides a global positioning system for the machine.

The data link is bidirectional. The bidirectional link allows the ECM to input information and output information. The data link consists of the following parts: internal ECM circuits, the related harness wiring, the service tool connector and the connector for the product link.

• The ECM receives commands from the Cat ET in order to change the operating modes. The Cat ET will read the service codes that are stored in the memory of the ECM. The Cat ET will clear the service codes that are stored in the memory of the ECM.

• The ECM sends the input and the output information to the Cat ET.

Note: An electronic control module that uses the Cat Data Link will have a module identifier (MID). The MID for the Machine Electronic Control Module is 039. The MID for the Transmission Electronic Control Module is 051. The MID for the Implement Electronic Control Module is 052.

CAN Data Link

A data link is required for communication with the Cat ET and the electronic control modules. The data link also communicates with the instrument clusters and other devices using this communications protocol. The data link is not used in order to broadcast any diagnostic information.