PLATE AS 1901684 - Caterpillar

ECM Pull Up Voltage
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 circuitsECM Pull Down Voltage
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.Inputs
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.Outputs
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.Input/Output
Communication between the ECM and the other control modules on the machine is conducted over data link circuits. The data link circuits