OpenHaldex — ESP32‑C6 Haldex Controller

OpenHaldex is an open‑source Haldex AWD controller for Volkswagen and Audi Group vehicles using Haldex Generation 1, 2 and 4 differentials.

The firmware runs on an ESP32‑C6 microcontroller and reads CAN bus messages from the vehicle, allowing the controller to modify or generate commands so the Haldex differential behaves exactly as configured.

Contents

• Features
• Purchase
• Overview
• Hardware
• Modes
• Expert Mode
• Installation
• Firmware Installation
• CAN Sniffing
• PCB & Enclosure
• Acknowledgements
• Disclaimer

Features

• Two TWAI (CAN) interfaces for reading and bridging CAN traffic
• Built‑in Wi‑Fi for on‑device configuration and diagnostics
• Multiple preset modes plus customisable mode profiles
• Tune your Haldex system directly from your phone via Wi-Fi

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Purchase

Assembled modules are available from Forbes Automotive if you do not wish to build one yourself:

➡ OpenHaldex C6 Controller – Forbes Automotive

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Overview

OpenHaldex sits between your vehicle and the OEM Haldex controller. It can operate as a passthrough (OEM behaviour), or modify messages to request different amounts of differential lock.

Supported generations: Gen1, Gen2 and Gen4

Gen3 and Gen5 are currently unsupported.

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Hardware

The PCB is based around an ESP32‑C6 Mini (with Wi‑Fi)

Two TWAI/CAN controllers are built into the PCB along with external IO control:

• External mode button
• On‑board RGB LED
• Brake / handbrake signals

There are also two high‑side drivers for brake/handbrake but these could be repurposed for other functions.

This platform replaces the earlier Teensy (OpenHaldex T4) design to provide better wireless support and on‑device configuration.

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Modes

The controller provides several preset modes along with a fully customisable mode:

Mode	Behaviour
Stock	OEM behaviour
FWD	Zero lock
7525	25% lock
6040	40% lock
5050	100% lock
Expert	User‑defined lock profile

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LED Indicators

5 mm onboard LED colour indicates the active mode:

Colour	Mode
Red	Stock
Green	FWD
Cyan	7525
Magenta	6040
Blue	5050
White	Expert

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Expert Mode

Expert mode allows lock targets to be configured based on speed and throttle setpoints using a table inside the Web UI. This is true full control over your Haldex system. No guesswork. You tune it and it'll do exactly what you want it to do, every time.

Expert mode grid configuration interface within the OpenHaldex C6 UI.

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Changing Modes

Modes can be changed using multiple interfaces:

On‑board button

Press the Mode button to cycle through modes.

Wi‑Fi

Use the Web UI at:

192.168.1.1 or openhaldex.local

CAN

Send a CAN message containing the mode number in Byte 0.

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Mode Numbers (CAN Byte 0)

Stock = 0
FWD = 1
5050 = 2
6040 = 3
7525 = 4
Expert = 5

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Broadcasted State

Default CAN ID:

0x6B0

The module broadcasts its current state on the CAN bus.

data[1] = standalone_flags (bitmask for Gen1/Gen2/Gen4)
data[2] = processed_haldex_engagement (mapped by firmware)
data[3] = lock_target_percent
data[4] = vehicle_speed
data[5] = mode_override_flag
data[6] = current_mode_number
data[7] = pedal_value

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Wi‑Fi Setup

1. Connect to the access point OpenHaldex‑C6
2. Open a browser and navigate to

192.168.1.1 or openhaldex.local

3. Access the Web UI

If the Wi‑Fi interface becomes unresponsive:

• Long‑press the Mode button to reset Wi‑Fi.

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Installation

Route cables as required and connect harness ends as described in the harness instructions.

For full step‑by‑step instructions see the OpenHaldex Installation Guide.

▶ Installation demo (YouTube Short): https://youtube.com/shorts/iUkNh9NbyKY?si=IhgqLIi0WM8wXqe9

• Haldex Connector — VW 1J0‑973‑713
• Vehicle Connector — VW 1J0‑973‑813

MX23A12NF Connector Pinout

Pin	Signal	Notes
1	Vbatt	+12 V
2	Ground/MALT	Ground
3	Chassis CAN Low	To chassis/ECU side
4	Chassis CAN High	To chassis/ECU side
5	Haldex CAN Low	To Haldex differential
6	Haldex CAN High	To Haldex differential
7	Switch Mode External	+12 V to activate
8	Brake Switch In	+12 V input
9	Brake Switch Out	Gen1 differentials only
10	Handbrake Switch In	+12 V input
11	Handbrake Switch Out	Gen1 differentials only

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Firmware Installation (ESP Web Tools)

Firmware can be installed directly from your browser using ESP Web Tools.
This is the recommended method for most users.

1. Connect the OpenHaldex controller to your computer using a data-capable USB-C cable.
2. Open the firmware installer page: Module Software Updater
3. Click Connect and select the OpenHaldex serial port.
4. Click Install and follow the prompts.
5. Wait for the firmware to flash and the device to reboot.

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CAN Sniffing (SavvyCAN / GVRET)

Enable Analyzer Mode in the setup menu to capture CAN frames.

SavvyCAN Connection

1. Connect to the OpenHaldex Wi‑Fi AP
2. In SavvyCAN select:

Add New Device Connection → Network Connection (GVRET)

3. Enter:

IP: 192.168.1.1
Port: 23

4. Set CAN speed:

500000

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PCB & Enclosure

Gerber files and enclosure designs are available in the PCB folder.

Pinout and functionality remain consistent across supported enclosure versions.

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Nice to Haves

• Flashing LED indicator when CAN message transmission fails

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Acknowledgements

• Forbes Automotive — Lead development of the OpenHaldex C6 platform, including reverse‑engineering and open‑source implementation for Gen2 and Gen4 Haldex systems, along with ongoing maintenance of the project
• A Banging Donk — Original OpenHaldex project for Gen1 vehicles
• Arwid Vasilev — PCB redesign (V1.02)
• LVT Technologies — OTA update integration (now deprecated, but still appreciated)

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Disclaimer