Group 36 MID 144 Vehicle Control Unit Design and Function MID 144 Vehicle Control Unit The manufacturer diagnostic tool is the preferred tool for performing diagnostic work. Contact your local dealer for more information or visit “www.premiumtechtool.com”. System Overview W2002673 Vehicle ECU The Vehicle Electronic Control Unit (VECU) is a microprocessor based controller, programmed to perform several functions, these include:
Driver controls Vehicle and engine speed controls Starter control Cab power Broadcasting data on the serial data lines Trip data logging Diagnostic fault logging and password processing 5th Wheel Slide Switch The VECU communicates with other modules and shares its inputs through the SAE J1939 high speed data link as well as the SAE J1587 normal speed data link. The SAE J1587 data link is primarily used for programming, diagnostics and data reporting. In addition to switch and sensor data, the broadcast between modules also includes various calculations and conclusions each module has developed, based on the input information it has received.
These calculations and conclusions are part of the modules on-board diagnostic capability. 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, the vehicle operator will be advised that a fault has occurred by the illumination of a malfunction indicator lamp and a message in the driver information display, if equipped. The VECU performs these functions by monitoring the signals from sensors and switches, and data received over the serial data lines from the other modules.
The VECU directly monitors the Throttle Position (TP) Sensor and Vehicle Speed Sensor (VSS). The VECU also monitors the position or state of multiple switches, to perform its control and diagnostic functions. The switches include: A/C Pressure Switch Air Suspension Height Control Switch Differential Lock Switch Engine Brake Switches Ignition Key Switch PTO Switches (if equipped) Service and Park Brake Switches Speed Control Switches (Set/Decel, Resume/Accel) When diagnosing an intermittent code or condition, it may be necessary to use a diagnostic computer connected to the Serial Communication Port.
Additional data and diagnostic tests are available when a diagnostic tool is connected to the Serial Communication Port. The VECU is mounted on a panel below the Fuse and Relay Center (FRC) in the center of the dash. For diagnostic software, contact your local dealer or visit “www.premiumtechtool.com”. 3