Troubleshooting
784C, 785B, 785C, 789B, 789C, 793B, 793C, 793D, 797 and 797B Off-Highway Truck/Tractors Vital Information Management System (VIMS)
General Information
Troubleshooting the Vital Information Management System requires additional information from the machine Service Manual, the Electrical System Schematic, and the Operation and Maintenance Manual.
As a guide, a "VIMS schematic" is provided in the Testing and Adjusting section of this manual. Refer to the Electrical System Schematic that is located in the machine Service Manual for a complete representation of the machine that is being diagnosed.
When the troubleshooting procedure instructs the service personnel to REPAIR THE HARNESS, always use the Electrical System Schematic that is located in the machine Service Manual to trace the circuit. Perform continuity checks at the connectors in order to locate the harness failures. At component connectors, always check the ground circuit. The power circuits of the control require less than 2 ohms of resistance between the ground contacts of the connector and frame ground. Signal circuits ("sensors, switches, solenoids etc.") require less than 5 ohms of resistance for normal operation. Resistance that is greater than 5 ohms can cause incorrect diagnosing of problems.
Repairs of the machine harness should be performed with wire of the same gauge. All joints should be soldered. All joints should be taped tightly. Use the 1P-0810 Vinyl Tape or shrink sleeving for all repairs to the harness. Repairs to the data link circuit in the harness must maintain the same "twist" ratio in the wiring that was provided in the original harness. The "two wires" of the Cat Data Link must maintain a twist rate of 2 ±1 turns per inch. Wiring of the display data link must maintain the twist rate of 2 ±1 turns per inch. The wires of the display data link are listed here: A251-BK (ground), C414-BU (Load), C413-YL (Data) and E708-PK (clock). Twisting is VERY IMPORTANT! Twisting will minimize the electrical interference to other circuits that is caused by the data link. Interference to the data link from other circuits will also be minimized.
During troubleshooting, inspect all component and harness connections before any component is replaced. Electrical problems can be caused if harness connections are not clean and tight. The electrical problem can be permanent or the electrical problem can be intermittent. Make sure that the connections are tight before other tests are made.
The failure of an electrical component can cause the failure of one or more related components. Always attempt to find the cause of the electrical system failure and then correct the cause of the electrical system failure before replacing a component.
Some machine functions that use solenoid valves require a suppressor diode across the valve coil. If the suppressor diode is faulty, electronic noise that is generated by the solenoids turning ON and OFF can cause erratic operation of the display components.
Data events and system events are defined by the machine's configuration software. Diagnostic functions for a given event are also defined in the configuration software. The VIMS 10.0X and later software use an improved "event definitions" in order to reduce the number of "nuisance events" for both machine and system conditions. An important change that was made to the software is the addition of a longer evaluation time. The longer evaluation time allows the VIMS to display an event only if an actual electrical failure exists. The VIMS may wait up to 8 SECONDS before displaying a system event on the message center or the VIMS may wait up to 8 SECONDS before storing a system event. During this time period, the gauges that are located on the "VIMS display components" may fall to the "red zone". The message area will show "ERR". During troubleshooting, allow an adequate amount of time for the VIMS to report that a new condition exists. For example, unplug a sensor from the machine harness. The VIMS may wait up to 8 seconds before reporting this condition as an "ERR". Some "system events" for filters may require SEVERAL MINUTES before the VIMS reports the condition. Likewise, when the condition is corrected, several minutes may be required before the event ceases to be reported. When the VIMS has received an event from an electronic control via the Cat Data Link, the VIMS adds zero time to these events. The VIMS displays the events immediately. The "event delay" is defined in the software of the control.
Repairs are considered complete when the system event is no longer present and the parameter appears to read the condition of the machine correctly.
Note: If an event is displayed for a bypass filters switch and the bypass switch has been replaced use the Electrical System Schematic as a troubleshooting aid. Check the components that are listed here: wire harness, the bypass switch and the ECM. Refer to the Testing and Adjusting, "Troubleshooting Switch Circuits" section.
Note: If consistent incorrect "fuel levels" are reported with no "reported faults", verify that the "program input" (contact 3) of the fuel level sensor is grounded "(the short tank configurations only)". If the contact is not grounded, repair the harness.
Quick Reference
* See the Troubleshooting, "Troubleshooting Diagnostic Codes Using Abbreviated Procedures" section for failures that have diagnostics (MID/CID/FMI).
* See the Troubleshooting, " Switch Circuits" section for failures in the operation of the alert indicator.
* For the "experienced service technician", see the Troubleshooting, "Troubleshooting Diagnostic Codes Using Abbreviated Procedures" section for troubleshooting failures that have diagnostics (MID/CID/FMI).
Note: Refer to the Special Instruction, REHS0126, "Diagnostic Code Information for Caterpillar Electronic Control" for information on diagnostic codes utilized by Caterpillar machines that are equipped with Caterpillar electronic controls.
