What is an Upfitter Electronic Module? (Explained)

Your vehicle is integrated with several modules as it features various sensors. Each module functions to reinforce the performance of your car while keeping the engine in good condition. 

The Upfitter Electronic Module is a computer that controls a specific vehicle part. The UEM not only allows you to control auxiliary equipment. It also enables you to access vehicle data without affecting other components. 

If you’re wondering how the UEM works and how you can reset it when it goes bad, this article comes in handy. Let’s get started. 

What is Upfitter Electronic Module and How does it work? 

Many automakers design vehicles to allow owners to add extra and special features to their vehicles and customize them. The computer in the car that enables you to achieve this is the Upfitter electronic module, UEM. The UEM, also called the Vehicle System Interface Module (VSIM) or Upfitter Interface Module (UIM) grants you access to your vehicle data. 

You can connect to a couple of functions and features without altering the performances of other components. What makes it possible is the built-in input commands, together with the J1939 communication bus output signals. The VSIM isn’t a dealer-installable device. Rather, it is manufactured with your vehicle and once assembled, the VSIM cannot be added. 

The Upfitter Electronic Module (UEM) is designed with some wired inputs and outputs. It is built purposely for UpfitRam trucks. UEM is needed for PTO capabilities or functionalities. But to make it work out, PTO must first be prepped on a vehicle before. PTO stands for Power Take-Off. It is a tool that transmits the mechanical power of an engine to another device without an engine.

The UEM enables the Upfitter to control specific functions using the J1939 or hardwire commands. The VSIM or UEM is available as a standard option. Its location is right behind the knee blocker (the trim covering the steering column), under the steering column. These hardware commands or connectors come with a vehicle’s VSIM. Gently remove the VSIM mounting bracket, using a screw tool. Then move the bracket and the VSIM to easily access the connectors. 

The upfitter module hardware drives standard automotive LEDs/relays and analog outputs and supports various OEM (original equipment manufacturer) baud rates and network protocols. It offers you access to control several accessories such as lights. The buttons are programmable through the EVIC (Electronic Valve Internal Combustion) so you can change how they function.  

Key Features of Upfitter Electronic Module

The model is an exclusive device that grants you access to connect to the vehicle’s different functions without literally cutting the wire. In addition, the computer’s features make it a lot more functional.

  1. Convenience: J1939 together with GM CAN, and FCA, all work to instantly generate a vehicle’s structural data. 
  2. Automatic sleep mode when inactive to reduce battery consumption
  3. Based on the vehicles data, the UEM enables other components like relay driver and output signals to control circuits
  4. Flexibility: Easy to operate output functions, due to user-friendly interface
  5. Extensive Control: Up to 4 or more inputs can control just one output.
  6. It makes troubleshooting easier through warning LED
  7. It has seven low true outputs, one high true output and two low true inputs.

VSIM Jumper Harnesses

When you order the upfitter package, you will receive a wiring harness (found in the spine of the cab in a compartment). These wires will help you connect your accessories to the system under the hood.

The VSIM jumper harness comes with a Vehicle’s VSIM. It has four different colored connectors. The Black, Brown and Green connect directly to the VSIM with the same cavity. Each colored connector has its number of cavities. 

Upfitter VSIM signals for Black connector include: High beam, Howler siren disabled, Driver seat belt not latched, Oil pressure warning signal, left turn signal and more. The Green connector signals include: Engine shutdown timer disable, Door unlock (all) function, Auxiliary/cluster lighting dimmer and more. 

Five of the Brown connector signals are Split shaft PTO – digital input, Rear bulb out detection off and three different PTO engine speed signals. All must be well plugged into the right labeled connector. 

Conditions under which VSIM may not function

The uplift components connected to the vehicle system interface module (VSIM) may malfunction at times. The reason is not far-fetched. 

  • VSIM signals will not function if the vehicle is not awake.
  • If VSIM locks become inactive
  • If the vehicle communication bus is inactive, all signals (Inputs, Outputs and J1939) will not work
  • If the key is turned in the off position while the vehicle is in sleep mode, the VSIM will not function. 

How to Diagnose inactive VSIM

It is possible to correct some of these issues by updating the VSIM with the newest software. The wiTECH is one device you can use to check if the VSIM is active on the Bus. If active, you can reset the part or install the latest software into VSIM. 

If the VSIM isn’t active, you can lower the VSIM and disconnect the connector to reset the module. You can find the VSIM beneath your car dash, near the park brake pedal. 

  • Press up on the module, 
  • Release the tab, 
  • Lower the VSIM. 
  • Disconnect the VSIM connector for 30 seconds

Once you complete this procedure and the VSIM remains inactive, you may need to contact your service manual to perform diagnostics.


What is Upfitter electronic module used for?

It is an electrical way of simplifying the mechanical structure of an engine or adding customized features. This depends on the needs of the vehicle owner. Auto owners ensure that making vehicle structural data available is critical and a component like the UEM comes in handy. 

Is Upfitter Electronic Module the same as VSIM?

Yes, the Upfitter Electronic Module (UEM) is the same as Vehicle System Interface Module (VSIM). In some other vehicles, the UEM is also called the Upfitter Interface Module (UIM). Although the name differs from vehicle model to model, the functions of the UEM are the same.  

What is the location of the VSIM connectors? 

The VSIM connectors face towards the front of the truck. You will find exactly along the direction where you face while driving your car. To access them, you will need to first pull out the VSIM mounting bracket and the VSIM. 

Final Wrap 

An Upfitter Electronic Module or VSIM provides augmentation for your vehicle. Through the VSIM, Upfitters gain reliable and quick access to your vehicle system. It contains different power components to simplify or change your vehicle’s design and reduce power. This includes changes to your vehicle’s chassis.

Upfitting allows you to enjoy more protective functions and other controls from your car. This not only meets your driving needs but also contributes to your daily efficiency. I hope this article helps you make an informed decision.


  • James Smith

    I'm James Smith, a car enthusiast and a content writer for Daily Car Tips. I have a passion for all things cars, from classic muscle cars to the latest electric vehicles. When I'm not writing about cars, you can usually find me tinkering with my car or checking out the latest automotive trends.