BMW I-Bus / K-Bus Firmware for ESP32 & Arduino

Control your classic BMW from your phone.
Ready-to-flash ESP32 firmware that puts the lights, windows, locks and trunk of your car on a web page — no app and no internet needed. A version for Arduino boards without Wi-Fi — Uno, Nano, Pro Mini, Mega — is included too. With transceiver schematics and wiring photos for the BMW E46.

Features · Quick Start · Web Interface · Hardware · Where to Connect · Messages · FAQ

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🌟 What Is This?

Classic BMWs link their body electronics over a single wire, the K-Bus. A small microcontroller on that wire can tell the light module, the body module and the windows what to do.

This repository is the firmware side of that idea: complete sketches you upload, connect and use. The ESP32 version creates its own Wi-Fi network and lets you control the car from a web page on your phone.

Firmware	Board	What it does
E46_KBus_ESP32	ESP32	Wi-Fi web interface to control the car from your phone.
E46_KBus_Code	Arduino Uno / Nano / Pro Mini / Mega	These boards have no Wi-Fi, so this version works from the remote key: welcome lights, goodbye lights and follow-me-home.
Basic_Code	Arduino Uno / Nano / Pro Mini / Mega	Bus reader that prints every message — useful to check your wiring.

Important

These sketches need the BMW IBus KBus library. It handles the bus communication — receiving, checksums and collision-free transmitting — and has to be installed before the sketches compile.

flowchart LR
    PHONE["Phone<br/>web interface"] <-->|"Wi-Fi"| MCU["ESP32"]
    MCU <--> TRX["Bus transceiver<br/>TH3122.4 · ELMOS 10026B"]
    TRX <--> CAR["BMW K-Bus<br/>12 V · single wire"]

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✨ Features

	Function	How it works
📱	Phone control	Lights, locks, trunk, windows, sunroof, interior light and wipers from any phone browser — no app, no internet.
🎚️	Settings on the page	Change the sleep timers and switch functions on or off; everything is stored on the ESP32.
🔎	Bus monitor	See the latest bus messages live in the web interface.
💤	Sleep mode	Powers down when the bus goes quiet and wakes up with the car, so it does not drain the battery.

Arduino boards have no Wi-Fi, so their firmware is driven by the remote key instead:

	Function	How it works
💡	Welcome lights	Press unlock — parking lights and turn signals come on. Press unlock again within about 15 seconds to add the fog lights.
👋	Goodbye lights	Press lock — the lights come on for 2 seconds as you walk away.
🏠	Follow-me-home	With the car locked, press lock twice within 4 seconds to keep the headlights on.

The ESP32 firmware includes these three as well; they can be switched off in the web interface.

🚀 Quick Start

1. Build the interface — the transceiver circuit connects the microcontroller to the 12 V bus.

2. Tap the bus — the CD-changer connector in the trunk gives you 12 V, ground and K-Bus in one plug.

3. Install the library — download the BMW IBus KBus library as a ZIP and add it in the Arduino IDE with Sketch → Include Library → Add .ZIP Library… It is also on its way into the Library Manager.

4. Get the firmware and open the sketch for your board in the Arduino IDE:

git clone https://github.com/muki01/BMW_IBus_KBus.git

5. Upload.

• ESP32 — open Codes/E46_KBus_ESP32, set your own Wi-Fi password in Config.h, select ESP32 Dev Module and upload. Then connect your phone to the BMW-E46 network and open http://192.168.4.1
• Arduino — open Codes/E46_KBus_Code, select your board (Uno, Nano, Pro Mini or Mega 2560) and upload. Disconnect the transceiver from D0 / D1 while uploading; the bus shares the hardware UART with USB.

📱 ESP32 Web Interface

Control	Monitor	Settings

The ESP32 creates its own Wi-Fi network and serves a single page that behaves like an app — it works without internet and without installing anything.

• Control — every button sends one message from E46_Codes.h. Filter by category — lights, locks, windows, interior, wipers — and see at a glance how long the ESP32 stays awake. The buttons are defined in Commands.h; add, remove or reorder a line to change the page.
• Monitor — the last 20 messages on the bus, newest first, with the sending and receiving module named.
• Settings — switch the key-fob light functions on or off, adjust both sleep timers and put the device to sleep. Settings are stored in flash.

How sleep works

The ESP32 does not use a sleep mode of its own. Exactly like the Arduino version, it is switched off completely by the bus transceiver and powered up again when the car wakes up.

Situation	Behaviour
The bus is active	The ESP32 stays on.
The bus has been silent for 60 s	The ESP32 pulls the transceiver's EN pin low. The transceiver goes to sleep and switches the ESP32's power supply off.
You used the web interface	It stays on for another 300 s after your last action, even if the bus is silent.
Any message appears on the bus	The transceiver wakes up and switches the power supply back on; the ESP32 starts again — for example when you press the remote key.

Both times can be changed on the Settings tab. The Control tab shows a countdown to the next sleep with a Stay awake button, and Sleep now is on the Settings tab.

Warning

Anyone who can join the Wi-Fi network can unlock the car. The firmware therefore has no default password and does not compile until you set your own in Config.h. Choose a strong one.

Note

The ESP32 firmware is experimental: it compiles on Arduino-ESP32 2.x and 3.x and the web interface has been tested in a browser, but it has not yet been verified in a vehicle.

🔧 Hardware

The bus idles at battery voltage, so a microcontroller must never be wired to it directly. The firmware is designed around the TH3122.4 / ELMOS 10026B bus transceiver:

Transceiver pin	Arduino	ESP32	Purpose
TXD	D0 (RX)	GPIO16	Bus → microcontroller
RXD	D1 (TX)	GPIO17	Microcontroller → bus
SEN/STA	D3	GPIO4	Bus-idle detection before transmitting
EN	D4	GPIO5	Keeps the transceiver on; pulled low to switch everything off
—	D13	GPIO2	Bus activity LED
—	D7 / D8	USB	Debug output

Arduino — powered from the transceiver's 5 V output. When the bus goes quiet the firmware pulls EN low, the transceiver switches its regulator off and the Arduino powers down with it. Bus activity wakes both again. The pins are the same on the Uno, Nano, Pro Mini and Mega 2560.

ESP32 — two things differ from the Arduino build:

• Power: the transceiver's regulator cannot supply an ESP32 with Wi-Fi, so the ESP32 gets its own 12 V buck converter with an enable pin. The transceiver's 5 V output — the pin that powers the Arduino — drives that enable pin instead. When the transceiver sleeps, the converter is off and the ESP32 draws nothing; when the bus wakes the transceiver, the converter starts and the ESP32 boots.
• Logic level: the transceiver uses 5 V logic and ESP32 pins are 3.3 V. Use a level shifter or voltage divider on the signals going into the ESP32 (TXD and SEN/STA).

The pins are set in Config.h.

Alternative interface circuits

Optocouplers (PC817) — built from common parts; well suited to reading the bus.

MCP2025 LIN transceiver — compact, with a built-in voltage regulator.

These circuits have no SEN/STA and EN pins, so the firmware's collision avoidance and sleep mode are not available with them.

🔌 Where to Connect (BMW E46)

The K-Bus is not available on the OBD-II port. These are the most practical places to reach it:

Option 1 — CD-changer connector (easiest)

Pre-wired in the trunk on most cars, even when no CD changer is installed. One plug provides everything you need.

1. Open the trunk — driver's side	2. Remove the trim to reach the bracket	3. The 3-pin connector X18180

Wire colour	Signal
⚪🔴🟡 White / red with yellow dots	K-Bus
🔴🟢 Red / green	+12 V
🟤 Brown	Ground

Option 2 — K-Bus junction block (above the fuse box)

The central splice point where every K-Bus branch of the car meets. Take the bus signal here and source 12 V and ground elsewhere.

1. Locate the connector block above the fuse box	2. Unclip it and pull it out
3. Find the K-Bus junction block	4. All white / red / yellow wires are K-Bus

Option 3 — Radio connector

The K-Bus wire (white / red / yellow) is also present in the radio harness behind the head unit.

📖 Message Reference

E46_Codes.h contains more than 100 ready-to-send messages for the E46. A selection is shown here with its checksum. Behaviour varies between models and equipment levels, so verify each one on your own car.

Events the firmware can react to

Message	Meaning
00 04 BF 72 22 EB	Key fob — unlock pressed
00 04 BF 72 12 DB	Key fob — lock pressed
44 05 BF 74 04 00 8E	Key inserted
44 05 BF 74 00 FF 75	Key removed
80 04 BF 11 00 2A	Ignition off
80 04 BF 11 01 2B	Ignition position 1
80 04 BF 11 03 29	Ignition position 2
50 04 68 32 11 1F	Steering wheel — volume up
50 04 68 32 10 1E	Steering wheel — volume down
50 04 68 3B 02 05	Steering wheel — R/T button

Lights

Message	Action
3F 0B BF 0C 00 00 00 00 7A 48 0A 06 B9	Parking lights + turn signals
3F 0B BF 0C 00 00 00 00 7A 48 0B 06 B8	Parking lights + turn signals + fog lights
3F 0B BF 0C 00 00 00 00 02 4E 0A 06 C7	Low beams
3F 0B BF 0C 00 00 00 00 62 08 A0 06 4B	Goodbye lights
3F 0B BF 0C 00 00 80 00 00 00 00 06 01	Follow-me-home
3F 0B BF 0C 00 00 00 00 00 00 01 06 80	Fog lights
3F 0B BF 0C 20 00 00 00 00 00 00 06 A1	Hazard lights
3F 05 00 0C 75 01 42	Hazard lights for 3 seconds
3F 05 00 0C 01 01 36	Interior light on

Windows, sunroof, locks and wipers

Message	Action
3F 05 00 0C 52 01 65	Driver window — open
3F 05 00 0C 53 01 64	Driver window — close
3F 05 00 0C 54 01 63	Front passenger window — open
3F 05 00 0C 55 01 62	Front passenger window — close
3F 05 00 0C 7E 01 49	Sunroof — open
3F 05 00 0C 7F 01 48	Sunroof — close
3F 05 00 0C 03 01 34	Central locking — toggle
3F 05 00 0C 34 01 03	Lock doors
3F 05 00 0C 02 01 35	Open trunk
3F 05 00 0C 49 01 7E	Front wipers
3F 05 00 0C 62 01 55	Front washer
3F 05 00 0C 4E 01 79	Alarm LED ("clown nose") for 3 seconds

Want to write your own functions? The message format, the API and the module address list are documented in the library repository.

📡 Supported Models

The firmware and message table were written for the BMW E46. The K-Bus itself is shared by many models, so the hardware and the library also work on the cars below — the messages may differ and need to be verified.

Chassis	Series	Years	I-Bus	K-Bus
E46	3 Series	1997–2006		✅
E38	7 Series	1994–2001	✅	✅
E39	5 Series	1995–2004	✅	✅
E53	X5	1999–2006	✅	✅
E83	X3	2003–2010		✅
E85	Z4	2002–2008		✅

📁 Repository Structure

BMW_IBus_KBus/
├── Codes/
│   ├── E46_KBus_ESP32/      ESP32 firmware: web interface for your phone
│   ├── E46_KBus_Code/       Arduino firmware: light functions from the remote key
│   └── Basic_Code/          Bus reader for checking the wiring
├── Schematics/              Transceiver circuits
└── images/                  Wiring photos and screenshots

The bus communication code lives in its own repository: BMW_IBus_KBus_Library.

❓ FAQ

Can I connect to the OBD-II port instead?

No. The K-Bus is the car's internal body network and is not present on the OBD-II connector. The line on the OBD-II port is the diagnostic K-Line — for that, see OBD2 K-line Reader.

Will it drain my battery?

No. Both versions are switched off completely by the transceiver when the bus goes quiet, and powered up again when the car wakes up. While the car sleeps, only the transceiver's own sleep current remains.

Which Arduino boards work?

The Arduino sketches build for the Uno, Nano, Pro Mini and Mega 2560. Boards with native USB such as the Leonardo and Micro are not supported as they are, because their Serial port is the USB connection and not a UART.

Why is there no default Wi-Fi password on the ESP32?

Because the web interface can unlock the car. A password that is published in a repository would let anyone nearby open every car running this firmware, so you have to choose your own before the sketch compiles.

Does it work on other BMWs?

The hardware and the library work on any car with an I-Bus or K-Bus. The messages in this repository were collected on an E46 and should be checked on other chassis before you rely on them.

How do I add my own button to the web interface?

Add one line to Commands.h with the group, the button text and the name of a message from E46_Codes.h. The page is built from that list.

🤝 Contributing

Contributions are welcome — especially:

• Test reports for the ESP32 firmware
• Verified messages for other chassis (E38, E39, E53, E83, E85)
• Wiring photos and connection points for other models

Please read the Contributing Guide and the Code of Conduct. Tested it on your car? Open a vehicle report with the model and year — real-world reports help everyone.

🔗 Related Projects

This firmware is part of a family of open-source automotive projects. They share the same hardware approach, so what you build for one carries over to the others.

Firmware — flash it and use it
BMW I-Bus / K-Bus Firmware you are here	Phone control and key-fob light functions for the BMW E46, on the ESP32 and Arduino.
OBD2 K-Line Reader	Scan tool for K-Line cars (ISO 9141-2, KWP2000) with a web dashboard, for the ESP32, ESP8266 and Arduino.
OBD2 CAN Bus Reader	Scan tool for CAN bus cars (ISO 15765-4) with the same web dashboard, for the ESP32.
VAG KW1281	KW1281 diagnostics for VW, Audi, Škoda and SEAT: ECU information, measuring groups and fault codes.
Libraries — build your own firmware
BMW IBus KBus Library	Receives, checks and sends BMW I-Bus and K-Bus messages; the library behind the BMW firmware.
OBD2 K-Line Library	K-Line diagnostics behind one API: ISO 9141-2, KWP2000, KW1281, DS2 and KW82.
OBD2 CAN Bus Library	OBD-II diagnostics over ISO 15765-4 with the ESP32's built-in CAN controller.
Interface
OBD2 Diagnostic UI	The web dashboard used by the two OBD2 readers.

💼 Custom Development

I design automotive diagnostic tools, firmware and hardware professionally. Whether you need a complete product or only the communication layer, I can help.

Service	Details
Protocol implementation	BMW I/K-Bus, K-Line (ISO 9141-2 / KWP2000), CAN / UDS, VAG KW1281 and other manufacturer-specific protocols
ECU communication & reverse engineering	Bus sniffing, packet decoding, module control, undocumented ECUs and buses
ECU security access	Seed-key algorithms and unlock routines for KWP2000 / UDS
Embedded firmware	Arduino, ESP32, ESP8266, STM32, Raspberry Pi Pico
Custom hardware	Diagnostic dongles, shields and PCBs designed to your requirements
Companion apps	Android, iOS and web apps to visualise, log and control your device

Have a project in mind? Reach out through the Contact section below.

📬 Contact

For custom development, collaboration, sponsorship or ready-made devices:

Channel	Address
📧 Email	muksin.muksin04@gmail.com
💼 LinkedIn	linkedin.com/in/muksin-muksin
🐙 GitHub	@muki01

☕ Support the Project

If this project helped you, consider supporting its development:

📈 Star History

⚠️ Disclaimer

Warning

This is a hobby and development project. Transmitting on a live vehicle bus can affect lighting, locking and other body functions. Test with the vehicle stationary, proceed at your own risk, and never operate the system in a way that distracts from driving. The author accepts no responsibility for damage or malfunction.

BMW is a registered trademark of BMW AG. This project is independent and is not affiliated with, endorsed by or sponsored by BMW AG.

📄 License

Released under the GNU General Public License v3.0.

• You are free to use, study, modify and share this firmware.
• If you distribute it — on its own or as part of a product or firmware — you must make the complete source available under the same license.

Closed-source or commercial product? A separate commercial license is available. Get in touch through the Contact section.

Copyright © 2023–2026 Muksin Muksin.

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Created by Muki · If this project helped you, please give it a ⭐

_{BMW · I-Bus · K-Bus · IBus · KBus · E46 · ESP32 · Arduino · web interface · welcome lights · follow-me-home · car hacking · TH3122}

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