What does the switch on the Forscan do

What does the switch on a FORScan adapter do?

A FORScan adapter is used to diagnose, program, and modify vehicle modules in Ford and Mazda cars. Since these vehicles use multiple communication buses (CAN networks) to manage various systems, an adapter capable of switching between them is required. This is where the switch on some FORScan adapters comes into play.

What is the purpose of the switch?

The switch on a FORScan adapter is used to manually toggle between two different CAN buses:

  1. HS-CAN (High-Speed Controller Area Network)
  2. MS-CAN (Medium-Speed Controller Area Network)

Ford uses HS-CAN to communicate with main control modules, such as the powertrain control module (PCM), ABS, transmission, and airbag. In contrast, MS-CAN is used for comfort and infotainment systems, such as climate control, door modules, and radio.

Since standard OBD2 adapters cannot automatically read MS-CAN data, an adapter with a physical switch is needed to allow the user to manually switch between these two networks.

How does the switch work in practice?

When you connect a FORScan adapter to your car's OBD2 port and start the FORScan software, the system will attempt to identify which modules are present in the car.

  • In HS-CAN mode (default mode):
    • FORScan can communicate with common modules such as PCM (Powertrain Control Module), ABS (Antilock Braking System), TCM (Transmission Control Module), IPC (Instrument Panel Cluster), and others that use high speed.
  • When FORScan asks you to switch to MS-CAN:
    • The software needs to communicate with modules located on the medium-speed bus. At this point, you must move the switch to MS-CAN mode.
    • After reading information from MS-CAN modules, FORScan may ask you to move the switch back to HS-CAN for further diagnostics or programming.

Why do some adapters not have a switch?

Some newer adapters have a built-in automatic switch between HS-CAN and MS-CAN. This means they do not need a physical switch – FORScan handles the switching automatically via the software.

How to use the switch correctly?

  1. Start FORScan and connect your adapter to the car's OBD2 port.
  2. Select the correct communication port in FORScan and connect to the vehicle.
  3. When FORScan asks you to switch to MS-CAN, move the switch on the adapter and confirm in the software.
  4. When you are finished with MS-CAN modules, move the switch back to HS-CAN and continue diagnosis or programming.

⚠ Important considerations:

  • Do not change the switch position when FORScan is actively communicating with a module – wait until the program prompts you to do so.
  • Ensure you have a compatible adapter; some cheap ELM327 clones have an unreliable switch and can cause errors during programming.

Summary

The switch on a FORScan adapter allows manual toggling between the HS-CAN and MS-CAN buses in Ford and Mazda cars. This is necessary to read and program all modules in the car, including comfort and infotainment systems.

---- Summary below ---

The switch on a FORScan adapter is used to toggle between different data networks in Ford vehicles. Ford uses multiple communication buses (such as HS-CAN, MS-CAN, and sometimes J1850), and certain modules are located on different buses.

Common modes on a FORScan adapter with a switch:

  1. HS-CAN (High-Speed CAN bus) – Default mode for most ECUs (engine, ABS, transmission, etc.).
  2. MS-CAN (Medium-Speed CAN bus) – Used for comfort systems such as door modules, infotainment, and climate control.

When using the FORScan software on a computer or mobile device, you may need to manually switch the toggle depending on which module you want to read or program.