V-MAC IV SYSTEM OVERVIEW Additional data and diagnostic tests are available when a diagnostic computer is connected to the Serial Communication Port. For diagnostic software, contact your local dealer. Five electronic control modules are used; the Engine Management System (EMS) Module, Instrument Cluster Module (ICM), Vehicle Electronic Control Unit (VECU), Transmission Electronic Control Unit (TECU) and the Gear Selector Electronic Control Unit (GSECU). Together, these modules operate and communicate through the J1939 high speed serial data line to control a variety of engine and vehicle cab functions.
The Engine Management System (EMS) Module controls fuel timing and delivery, fan operation, engine protection functions, engine brake operation, the EGR valve, and the turbocharger nozzle. The Vehicle Electronic Control Unit (VECU) controls cruise control functions, accessory relay controls and idle shutdown functions. The Instrument Cluster Module (ICM) primarily displays operational parameters and communicates these to the other ECU’s. All have the capability to communicate over the J1587 normal speed data lines primarily for programming, diagnostics and data reporting.
The Instrument Cluster Module (ICM) is mounted behind the driver's steering wheel and is the main control center for dashboard functions. The ICM is used to provide the operator with information via gauges, indicator lamps and a display. Via the three connectors on the rear of the instrument cluster module, information from the whole vehicle is received. Some information is received from sensors directly connected to the instrument panel, and some is received across the J1708/1587 data link. The data link permits other control units in the vehicle to send messages to the instrument panel.
The instrument panel receives these messages, processes them and then presents the information in a suitable form to the operator. The operator can use a control stalk on the steering column to cycle through a set of menus to gain a more detailed picture of the vehicle status. In addition to their control functions, the modules have on-board diagnostic capabilities. The on-board diagnostics are designed to detect faults or abnormal conditions that are not within normal operating parameters.
When the system detects a fault or abnormal condition, the fault will be logged in one or both of the modules' memory, and the vehicle operator will be advised that a fault has occurred by illumination of the Malfunction Indicator Lamp. The module will also initiate the engine shutdown procedure if the system determines that the fault will damage the engine. The Vehicle Electronic Control Unit (VECU) is mounted on a panel below the top dash access panel in the center of the dash on conventional models. The VECU is a microprocessor based controller programmed to perform several functions, these include:
Driver Controls Vehicle and engine speed controls Starter control Cap Power Idle controls In some situations when a fault is detected, the system will enter the "limp home" mode. The limp home mode allows continued vehicle operation but the system may substitute a sensor or signal value that may result in poor performance. In some instances, the system will continue to function but engine power may be limited to protect the engine and vehicle. Fault codes logged in the system memory can later be read, to aid in diagnosing the faults, with a diagnostic computer or through the instrument cluster display, if equipped.
When diagnosing an intermittent code or condition, it may be necessary to use a diagnostic computer connected to the Serial Communication Port. Broadcasting data on the serial data lines Trip data logging Diagnostic fault logging and password processing The VECU performs these functions by monitoring the signals from sensors and switches, and data received over the serial data lines from the other ECU's. The VECU directly monitors the Throttle Position (TP) Sensor Vehicle Speed (MPH) Sensor (VSS). Page 6 DESCRIPTION AND OPERATION