Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Module, Vehicle System Interface (VSIM): Operation
The microcontroller-based electronic Vehicle System Interface Module (VSIM) contains the electronic logic circuitry and software that enable many of the aftermarket equipment and systems typically installed on police or fleet vehicles to communicate with and be integrated with the Electronic Control Units (ECUs) and features already installed in the vehicle. The VSIM can communicate with aftermarket ECUs or with other ECUs in the vehicle using the Controller Area Network-Chassis (CAN-C) data bus.
The VSIM is powered by a fused B(+) circuit and is grounded at all times so that it can operate regardless of the ignition position. The VSIM awakens or sleeps based upon the status of the CAN-C data bus. The VSIM monitors both active and stored Diagnostic Trouble Codes (DTC) through On-Board Diagnostics (OBD) and communicates with a diagnostic scan tool using the CAN-C data bus.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.