FORScan for Mazda: What You Can Change and How to Start
FORScan is a Windows diagnostic and module-configuration tool that talks to vehicle ECUs through the OBD-II port. On Mazda SkyActiv cars it lets you change settings stored in the body control modules, instrument cluster, and other ECUs — door-lock behavior, daytime running lights, i-Stop defaults, and similar. These modules are separate from the CMU infotainment unit, so FORScan changes survive CMU firmware updates, factory resets, and battery disconnection.
What FORScan Can Change
Section titled “What FORScan Can Change”FORScan edits ASBuilt data in the body modules. That covers a different set of features than the CMU infotainment screen:
| FORScan (module config) | CMU (infotainment) |
|---|---|
| Auto door lock/unlock behavior | Disclaimer screen |
| DRL configuration | Touchscreen-while-driving lock |
| i-Stop default state | Boot time |
| Find My Car (horn honk) | Custom apps and gauges |
| Emergency Stop Signal (ESS) | Visual themes |
| Headlight off timer | Audio/UI behavior |
| Cruise control display type | — |
The two are independent. A FORScan change lives in the RBCM, FBCM, SSU, or IC; nothing you do to the infotainment unit touches it, and vice versa.
Most Popular Changes
Section titled “Most Popular Changes”| Change | Module | Hardware needed | Notes |
|---|---|---|---|
| i-Stop default OFF | SSU | No | Starts each drive with i-Stop disabled; the button still toggles it manually. |
| Auto door lock/unlock | RBCM | No | Locks at speed, unlocks on ignition off. Exposes new options in CMU settings. |
| Find My Car (horn on double-lock) | RBCM | No | Double-press lock on the fob honks the horn and flashes the hazards. |
| Emergency Stop Signal (ESS) | FBCM | No | Rapid hazard flash under hard braking above ~60 km/h. |
| DRL configuration | FBCM | No | Change the DRL source: parking lights, low beams, or turn-signal lamps. |
| Headlight off timer | RBCM | No | Keeps headlights on 15–180s after shutdown via a high-beam stalk pull. |
| Fog lights with high beams | FBCM | Fog lights | Overrides the factory fog-light shutoff when high beams come on. |
| Auto-fold mirrors on lock | RBCM | Power-fold mirrors | Folds mirrors when locking. Requires power-fold hardware. |
| Auto Hold default ON | EPB | Electronic parking brake | CX-5 KF (2017+) only. Auto Hold defaults to ON each start. |
| Cruise control display type | IC | Cruise stalk | Switch between standard CC, CC with speed limiter, and MRCC display. |
Every change is reversible by restoring the original ASBuilt values. The vehicle-specific pages below give exact byte addresses and checksum steps for each car.
Requirements
Section titled “Requirements”Software
Section titled “Software”- FORScan for Windows. Download from forscan.org.
- The free version reads modules. Writing ASBuilt data needs the extended license (about $10–15/year).
- FORScan Lite (iOS/Android) has limited module access — use the full Windows version for configuration work.
- Windows-only. On Mac or Linux, run it in a Windows VM (Parallels, VMware, VirtualBox) or Boot Camp.
Hardware
Section titled “Hardware”You need an OBD-II adapter with MS-CAN (medium-speed CAN) support. The Mazda body modules sit on MS-CAN, not the standard HS-CAN bus, and most cheap adapters only talk HS-CAN. See the adapter buying guide for specific adapters and how to switch each one between HS-CAN and MS-CAN.
Knowledge
Section titled “Knowledge”- Back up all ASBuilt data before changing anything.
- Understand the checksum system — many blocks reject a write unless the checksum is recalculated.
- Know which modules your specific car actually has before enabling a feature.
CAN Bus Architecture
Section titled “CAN Bus Architecture”Mazda SkyActiv cars expose two CAN buses through the OBD-II port:
| Bus | Speed | Modules | Scanned by default? |
|---|---|---|---|
| HS-CAN (high speed) | 500 kbit/s | PCM, TCM, ABS, EPS | Yes |
| MS-CAN (medium speed) | 125 kbit/s | RBCM, FBCM, SSU, IC | No — requires adapter mode switch |
The popular changes all target modules on MS-CAN: door locks, DRL, i-Stop, ESS. Switch the adapter to MS-CAN before scanning, or those modules never appear.
Backup First
Section titled “Backup First”Back up ASBuilt data for every module before you change anything. A backup is the only clean way to revert.
- Connect the adapter and switch it to MS-CAN mode.
- In FORScan, scan for modules. You should see RBCM, FBCM, SSU, and IC at minimum.
- For each module: open it → ASBuilt Data → Read → Save to file.
- Name backups with a date and description, e.g.
RBCM_stock_2024-01-15.abt. - Repeat for every module you plan to touch.
With a backup, reverting is writing the original values back. Without one, you’re hunting for stock values in the community or accepting the risk of restoring the wrong data. The full walkthrough is on the ASBuilt backup and restore page.
Checksums
Section titled “Checksums”Many ASBuilt blocks on Mazda SkyActiv modules include a checksum byte. Change the data without recalculating it and FORScan rejects the write, or the module quietly stores corrupted data.
- Each block has a specific byte position designated as the checksum.
- The checksum is computed from the other bytes in the block.
- The algorithm varies by module.
The Mazda SkyActiv OBD-II Calc spreadsheet (by SergSlimMazda, versions v7.00–v7.09, on Scribd and the Mazda forums) automates this: paste in your current hex, flip the bits you want, and it recalculates the checksum byte for you. Write the complete block, new checksum included, to the module.
Do not hand-edit hex without recalculating the checksum.
Common Mistakes
Section titled “Common Mistakes”| Mistake | Consequence | Prevention |
|---|---|---|
| Not switching to MS-CAN | Body modules don’t appear | Switch adapter mode before scanning |
| No backup before changes | Can’t cleanly revert | Back up every module first |
| Wrong checksum | Write rejected or data corrupted | Use the calc spreadsheet |
| Enabling ADAS without the hardware | Warning lights, stored DTCs | Confirm the physical sensors exist |
| Writing to the PCM without expertise | Driveability problems | Leave the PCM alone unless you’re sure |
| Modifying safety modules (ABS, airbag) | Safety-system malfunction | Don’t touch these |
Safety Boundaries
Section titled “Safety Boundaries”Safe to change — software-only features: door-lock behavior (RBCM), DRL configuration (FBCM), i-Stop default (SSU), Find My Car horn honk (RBCM), ESS (FBCM), headlight timer (RBCM), blinker on lock/unlock (RBCM), cruise control display type (IC).
Leave alone unless you fully understand the module: PCM (powertrain — affects driveability), ABS/DSC (braking behavior), airbag/SRS (occupant safety), EPS (steering assist).
Requires the physical hardware to be present: ADAS features (LDWS, HBC, SCBS, BSM, MRCC) throw warnings if enabled in the IC without sensors; camera path lines need a CAN-connected reverse camera; lane-keep assist (LAS) needs the FSC camera plus an LAS-capable EPS.
No FORScan change is physically permanent. Anything you write, you can write back.
Vehicle-Specific Guides
Section titled “Vehicle-Specific Guides”Exact byte addresses, supported features, and checksum notes differ by model:
A first session, backup included, runs about 30–60 minutes.