Vehicle CAN Bus Addon#

The standard comma harness only connects to the Party CAN bus, which is sufficient for steering and cruise control. However, some features require access to the Vehicle CAN bus — a separate bus that carries infotainment and body data.

The Vehicle CAN Addon Cable adds two wires (blue and pink) to your existing comma harness via Molex iGrid terminals. The addon cable then plugs into the diagnostic connector on the A-pillar — the same location where the popular S3XY Buttons Commander by enhauto connects.

This upgrade works with both HW3 and HW4 harnesses purchased from comma.ai or xnor.shop.

LHD only: This addon is designed for left-hand drive vehicles. On RHD cars the autopilot computer sits on the left side while the X179 A-pillar connector is on the right, requiring a cable run across the entire car. For this reason, the addon cable is only offered for LHD.

Where to insert the wires#

The two Molex iGrid terminals are inserted into your existing comma harness connector:

Molex terminal insertion

A-pillar connector location#

The Vehicle CAN bus connector is located on the right A-pillar (regardless of left- or right-hand drive). You access it by removing three plastic trim panels:

A-pillar connector X179

What does the Vehicle CAN bus enable?#

Full MADS support#

In stock openpilot, steering and speed control always engage and disengage together — pressing the brake turns off everything. Sunnypilot offers MADS (Modular Assistive Driving System), which keeps steering active even when you press the brake, so you can drive normally with both pedals. Without the addon, you’re limited to one-pedal driving (gas + regen only), because pressing the brake disengages openpilot entirely.

MADS is engaged by tapping the infotainment screen with three fingers. This gesture generates a CAN message that only exists on the Vehicle bus, which is why the addon cable is required.

Beyond MADS#

The Vehicle CAN bus also carries the same commands used by the Tesla app — opening the trunk, controlling climate, etc. None of this is implemented in openpilot yet, but the addon makes it accessible for anyone who wants to develop custom features.