A MODULE THAT READS YOUR ELECTRIC CAR DIRECTLY, SO THE TRACKING AND PREHEATING DO NOT GO THROUGH THE MANUFACTURER
Plug this into your car's diagnostic port and the data goes to your server, not the manufacturer's — including the ability to send commands back.
by Open Vehicle Monitoring System team
AutomationOpen-hardware
- difficulty
- ●●●●○
- time
- a weekend-plus
- license
- MIT
- repo
- repo ACTIVE836 stars
●●●●○ · a weekend-plus · MIT · 836 stars · repo ACTIVE
WHAT YOU’LL NEED
- 3D printer + filament — printable parts — files are in the repo
- Electronic parts — full list with part numbers in the repo BOM
- Dev board / microcontroller — runs the project firmware
Partner
COMPAREE VERDICT
OVMS is for someone who wants full control over their EV telemetry and is prepared to solder a board, flash firmware and read a CAN bus datasheet to make that happen. The hardware is well-documented and the firmware is mature, but this is not plug-and-play: you will spend time mapping signals for your specific car and year if someone has not already done it. The payoff is genuine independence from manufacturer apps that go dark when support ends or subscription terms change. The single thing most likely to go wrong is discovering halfway through that your car model has incomplete or outdated support in the repo, which turns a weekend into a reverse-engineering project. If your car is on the tested list and you are comfortable with embedded development, this is exactly what it claims to be. If you have never configured a CAN filter or compiled ESP-IDF firmware, start with something simpler.
IN THE REPO
NOT IN THE REPO
- —Full hardware design (Altium and KiCad exports), firmware source, build guide and per-vehicle configuration modules are all in the repo under MIT licence.
- —A working build requires soldering surface-mount components, sourcing cellular and GPS modules, and configuring the firmware for your specific car model.
- —Vehicle support is contributed by owners — coverage is good for popular EVs (Nissan Leaf, Kia e-Niro, Renault Zoe, Tesla, VW e-up) but patchy for rarer models.
- —You will need a cellular data plan for the GSM modem and a server to receive the telemetry (self-hosted or the project's free community server).
- —The module reads and writes to the car's CAN bus — errors in configuration or commands can trigger dashboard warnings or fault codes.
- —MIT licence permits commercial use.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
Partner · KickstarterHeyGears G1: 10M+ colors and transparent parts in one print, plus UV printing on flat objects. Figures, parts and labels — no painting.
Gallery
Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Check vehicle support (Start in the vehicle/ directory — each supported car has a subdirectory with notes on what works and what does not. If your model is missing or marked incomplete, expect to do CAN reverse engineering.)
- 2.Read the hardware guide (The docs/ folder has build instructions, BOM and pinouts. The Altium source is in the hardware/ directory; KiCad exports are also provided.)
- 3.Order or fabricate the PCB(Gerbers are in hardware/ — upload to your preferred fab house. A two-layer board, no exotic specs.)
- 4.Source components and solder(BOM is in the docs. Most builders report the SIM800 and GPS modules as the longest-lead items. Surface-mount soldering required.)
- 5.Flash firmware and configure for your car (Firmware build instructions are in the repo root README. Vehicle-specific configuration goes in the relevant vehicle/ subdirectory.)
Resources
Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.
- User guide and build docs github.com
- Vehicle support directory github.com
- Project site openvehicles.com
KNOWN ISSUES
- The biggest trap is assuming your car is fully supported because it appears in the vehicle list — many entries are partial, covering only basic telemetry or specific model years. Read the notes file for your car before ordering parts.
- The SIM800 GSM module is 2G-only, which is being phased out in some countries. Check that your carrier still supports 2G before buying, or plan to substitute a 4G module (requires firmware changes).
- CAN bus wiring varies by model year even within the same car. The OBD-II pinout is standard, but the signals on those pins are not — a configuration that works for a 2019 Leaf may not work for a 2021.
- The module draws power from the car's OBD port, which on some vehicles is always live. A runaway firmware loop or misconfigured sleep mode can flatten the 12V battery if left plugged in.
- If you use the project's community server, your telemetry is visible to other users by default unless you configure privacy settings. Self-hosting avoids this but adds server setup to the build time.
- Sending the wrong CAN message can put the car into a fault state that requires a dealer reset. Test every remote command (charge start, climate control) while standing next to the car before relying on it from distance.
Do I need to keep this plugged in all the time?
No — you can unplug it when not needed. But if you want continuous telemetry and remote commands, it stays in the OBD-II port. Some builders add a switch to isolate it from the car's 12V bus when parked long-term.
Will this void my car's warranty?
Plugging into the OBD-II port is legal and common, but sending CAN commands (charge start, climate control) writes to the bus in ways the manufacturer did not intend. Whether that voids warranty depends on your dealer and jurisdiction — there is no universal answer.
Can I use this to unlock paid features or increase range?
No. OVMS reads and sends the same messages the car already understands — it does not modify firmware or bypass restrictions. If a feature is software-locked by the manufacturer, this will not unlock it.
What happens if my car model is not in the supported list?
You can add support yourself by reverse-engineering the CAN messages, which requires a logic analyser, the car's service manual (if available), and time. The repo has a guide for adding new vehicles, but this is not a weekend task — expect weeks.
Do I need the project's server or can I run my own?
You can do either. The project provides a free community server, or you can self-host the server component (also open source, in the repo). Self-hosting gives you full control but requires a VPS or home server with a static IP.
Community builds
No community builds yet — be the first, we feature the best ones.
Discussion1
FROM THE COMPAREE TEAM
836 stars and active development as of August 2026, with per-vehicle modules spanning everything from the Nissan Leaf to the VW e-up — which car would you add support for if yours is not on the list yet?
Open Vehicle Monitoring System team
OVMS started as a single-car project to keep a Roadster connected after Tesla's early telematics systems aged out, then grew into a community effort as other EV owners faced the same problem with different manufacturers. The hardware is now on its third major revision, with contributors from across Europe, North America and Australia.
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DISCLAIMER
- Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM13d ago
Practical notes from our verification: the hardware has been stable since v3.2, the last major board revision, and the repo includes both Altium source and KiCad exports so you are not locked to one tool. The biggest variable is vehicle support — popular EVs like the Leaf and Zoe have multiple contributors keeping the configuration current, while rarer models have single-person support that can go stale between firmware updates. If your car is not fully documented, budget time to learn CAN bus reverse engineering, not just soldering. The 2G modem is the one ageing component — several builders in the discussions have already swapped to 4G modules, though that requires firmware changes the repo does not yet merge by default.