STUD 1869719 - Caterpillar

diagnostics for the ECM can be accessed through one of the following tools: the Operator Monitoring System and Cat® Electronic Technician (Cat ET) Service Tool. To troubleshoot the electronic control system of the machine, additional information is required from the Service Manual of the machine. The following list contains some of the required support materials:
Systems Operation, UENR2964, "320D2 and 323D2 Excavators"
Testing and Adjusting, UENR2963, "320D2 Excavator"
Operation and Maintenance, SEBU9008, "320D2 Excavator"
Electrical Schematic, UENR5968, "320D2 Excavator Electrical System"
Hydraulic Schematic, UENR3603, "320D2 and 320D2 GC Excavator Hydraulic System"As a guide, a typical system schematic is included at the end of this manual. For an accurate representation of the machine that is being diagnosed, refer to Electrical System Schematic in the Service Manual.When the troubleshooting procedure instructs you to “REPAIR THE HARNESS OR REPLACE THE HARNESS”, use the Electrical System Schematic for the machine that is being serviced to trace the circuit. Perform continuity checks at the harness connectors to locate harness failures. At the connectors of the components, always check the ground circuit. Less than 5 Ω of resistance is required between the ground contacts of the connector and the frame ground. The power circuits of the ECM should have less than 2 Ω of resistance between the contacts of the ground connector and the frame ground. Less than 5 Ω of resistance is required for signal circuits for normal operation. Excessive ground resistance that is greater than 5 Ω can cause incorrect diagnosing of problems.During troubleshooting, inspect all connections before any component is replaced. If these connections are not clean and tight, permanent electrical problems or intermittent electrical problems can result. Check that the wires are pushed into the connectors completely. Make sure that the connections are tight before other tests are made.Failure of an electrical component can cause the failure of other components. Also, failure of an electrical component can be caused by the failure of other components. Always attempt to correct the cause of an electrical system failure before you replace a component.