PLATE 2292459 - Caterpillar

Illustration 1 g01309473
ECM Connectors and ContactsThe Power Train ECM is located under the left console.The ECM makes decisions that are 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 ECM sends the information to the Caterpillar Electronic Technician service tool on the Cat Data Link.Note: The ECM is not serviceable. If the ECM fails or if the ECM is damaged, the ECM must be replaced. The failure rate for the ECM is very low. If the ECM is suspected to be faulty when there is a problem with an electrical circuit on the machine, replace the ECM only after all of the other possible causes of the problem have been investigated.ECM Pull Up Voltage
In order to aid in diagnostics of certain types of electrical circuits that are controlled by the ECM, an internal "pull up voltage" is connected to ECM switch and sensor signal input contacts. An above normal voltage is internally connected to the ECM signal input circuit through a resister.During normal operation, the switch or sensor signal will hold the circuit low or at a certain signal amplitude, however, circuit conditions such as a loss of power to the component, a disconnection or an open circuit will allow the circuit to be pulled high by the ECM pull up voltage. This will result in an above normal voltage condition at the ECM contact. As a result, the ECM will activate a 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 that are controlled by the ECM, an internal "pull down voltage" is connected to ECM switch to battery type input circuits. During normal operation, the switch contacts that are allowing the connection to a voltage source will hold the circuit high. When circuit conditions such as a loss of power to the switch supply voltage, a disconnection in the switch circuit or an open circuit will allow the circuit to be pulled low by the ECM pull down voltage. This 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 and 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.