Note: The ECM is not serviceable. If the ECM is damaged, the ECM must be replaced. The ECM failure is unlikely. If the ECM failure is suspected, contact the Technical Communicator at a local dealership for possible consultation with Caterpillar before replacing the ECM. Replace the ECM only after all of the other possible causes of a particular problem have been investigated.
To aid in diagnostics of certain electrical circuits, an internal "pull up voltage" is connected to the ECM switch and sensor signal input contacts. An above normal voltage is internally connected to the ECM signal input circuit through a resistor.
During normal operation, the switch or sensor signal will hold the circuit low or at a certain signal amplitude. When circuit conditions such as a loss of power to the component, a disconnection, or an open circuit, the ECM circuit will be puled high by the pull up voltage. The pull up voltage will result in an above normal voltage condition at the ECM contact. As a result, the ECM will activate an FMI 03 (voltage above normal) diagnostic code for the affected circuit.
The types of ECM input circuits that have pull up voltage present are:
- Pulse Width Modulated (PWM) sensor input circuits
- Switch to ground switch input circuits
- Active analog (voltage) input signal circuits
- Passive analog (resistance) input signal circuits
In order to aid in diagnostics of electrical circuits controlled by the ECM, an internal "pull down voltage" is connected to the ECM switch to battery input circuits.
During normal operation, the switch contacts that are allowing the connection to a voltage source will hold the circuit high. When conditions like a loss of power to the switch supply, switch circuit disconnection, or an open circuit, will allow the ECM circuit to be pulled low by the pull down voltage. The pull down voltage will result in a below normal voltage condition at the ECM contact. As a result, the ECM will activate an FMI 04 (voltage below normal) diagnostic code for the affected circuit.
The machine has several different types of input devices. The ECM receives machine status information from the input devices. The ECM determines the correct output action that is needed in order to control machine operations based on memory and software parameters. The machine utilizes the following types of inputs: switch type and sensor type.
Switches provide signals to the switch inputs of the ECM. The possible outputs of a switch are listed: an open signal, a grounded signal and + battery signal.
Sensors provide an electrical signal to the ECM that constantly changes. The sensor input to the ECM can be one of several different types of electrical signals such as: pulse width modulated (PWM) signals, voltage signals and frequency input signals. Refer to the correct pilot machine schematic to verify each input to the ECM.
The ECM sends electrical signals through the outputs. The outputs can create an action or the outputs can provide information to the ECM. The ECM can send output signals to the system components in one of several different electrical signal types such as: driver outputs, sinking driver outputs, sensor power supply outputs and data link outputs. Refer to the correct pilot machine schematic to verify each output to the ECM.
Communication between the ECM and the other control modules on the machine is conducted over data link circuits. The data link circuits allow the sharing of information with other electronic control modules. The data link circuits are bidirectional. The data link circuit allows the ECM to send information and to receive information.
The ECM supports two types of data link systems.
- Cat® Data Link
- SAE J1939 Data Link
The two types of data links are the main structure for communication between all of the control modules on the machine. More than one CAN data link system can be present on a machine. Dedicated CAN data link circuits can be used for communication between specific controls on the machine.
Communication between the ECM and the other control modules on the machine are conducted over the J1939 Data Link circuit. The J1939 Data Link circuit is connected to each control module. The ECMs use the Cat Data Link to send and receive information from the Cat® Electronic Technician (Cat ET) Service Tool.
A module identifier (MID) is assigned to each ECM on a machine. For example, the MID for the Machine ECM is 299.