Comma 3X Rivian Gen 1
Install Tips and Tricks

!!  IMPORTANT  !!
To prevent issues with Rivian’s sensitive electronics, we strongly recommend
your Rivian is asleep during the installation of the Comma harness.  
(Follow instructions in the Install in Sleep Mode section.)

Table of Contents

Driver+ vs. Openpilot        2

Hardware Install Guides        2

Support        2

Hardware        3

Required        3

Optional        3

Tools        4

Required        4

Helpful        4

Tips and Tricks        5

Autonomy Experience Module (AXM)        5

Install in Sleep Mode        6

Harness Install        7

Cable Routing        8

Installing a Power Source        10

Disconnecting AXM Power        12

Windshield Placement        14

Magnetic Mounts for Quick Release        14

Magnetic Mounts + Longitudinal Upgrade        15

Troubleshooting        17

Comma Connect        19

Set up Your Account and Share Routes        20

Create and Share Clips        20

Sunnypilot        20

Installation        20

Version Comparison Table        22

Glossary        23

Driver+ vs. Openpilot

Driver+ and Openpilot are Level 2 automation systems. They can assist with steering, acceleration and deceleration, but the driver must remain engaged and ready to take over at any time.

        * ADAS = Advanced Driver Assistance System

        ** Within reason. Openpilot may not function properly in every situation.

Hardware Install Guides

We recommend you use the Comma Power OBD-II harness or a Fuse Tap 
to ensure clean, isolated power to your Comma 3X.

Support

• Discord - Comma Rivian
• Discord - Sunnypilot Rivian
• Openpilot - Wiki

Hardware

Required

*   includes 8-degree mount + 8’ USB-C 3.1 cable

** includes Fuse Tap

** support our lead Rivian port developer!

Optional

• Longitudinal Upgrade Kit + 8’ USB-C cable

• Allows use of Openpilot Longitudinal in place of Rivian ACC
• Only supported by sunnypilot, a community-developed fork
• Set cruise speed using the steering wheel buttons
• Choose driving personalities (follow distance) using the scroll wheel
• Use Rivian’s blind spot monitors (BSM) with auto lane changes

• Magnetic Mount (for quick and easy Comma disconnect)

• Beartech Magmount + 8-degree mount - Install Guide
• Chun Quick Mount
• Janka Cross Glide Mag Mount

If you have a Magmount and the Longitudinal Upgrade Kit (which requires a second USB-C cable), the adapters below allow you to still quickly remove your Comma 3X.  Refer to the Magnetic Mounts + Longitudinal Upgrade section for installation details.

These adapters can only be used on the secondary OBD-C port!

See the Magnetic Mounts section for more information.

• USB-C Extender Adapter

• Plugs into the secondary OBD-C plug on the Comma 3X

• USB-C Magnetic Adapter

• Sits between the extender and the second USB-C 3.1 cable

Tools

Required

• Torx T20 screwdriver (to remove two screws holding up the footwell cover)
• Flathead screwdriver (to unplug, manipulate and push in the harness connector)
• Light source (to see what the hell you are doing back there)

• Floor lamp and/or Headlamp

• Plastic trim tool (for removing panels and  routing the USB-C cable)

• Trim tool set on Amazon

Helpful

• Socket wrench with extender and ½” socket (to remove the fuse panel bolt)
• L-shaped tool (to grab and manipulate the harness connector)

• Hook set on Amazon

• Long needle-nose pliers (to hold and manipulate the harness connector)
• Small hands, long fingers (to reduce the level of frustration)

Tips and Tricks

Autonomy Experience Module (AXM)

To give you an idea of what you’re working with, below is a side view of the AXM.  

Inside the passenger footwell,

1. You are looking at the AXM in the direction of the blue arrows.
2. You can remove the white connector in the green rectangle for easier access.
3. The Comma harness connector will slide into the slot in the yellow rectangle.  

(Fun Fact:  This module is water-cooled!  Red rectangle highlights the coolant pipes.)

Install in Sleep Mode

!!  STRONGLY RECOMMENDED  !!

There have been several instances where Driver+ was deactivated
and unrecoverable after connecting the Comma harness with Rivians awake.  
The Comma 3X may also not receive power.

To avoid this potential issue, install the Comma harness with your Rivian in sleep mode. To accomplish this, follow these steps:

1. Turn off Gear Guard.
2. Open the passenger door, lock your Rivian and leave the door ajar.
3. Turn off Bluetooth on your phone.
4. Walk away for 15-20 minutes to allow the Riv to enter sleep mode.
5. If you have one, keep your key fob out of range.
6. If you have your phone connected to the Riv’s WiFi hotspot, turn that off.
7. Return to your Riv on the passenger side and ensure all screens are off and remain off during installation.
8. Be sure not to put any weight on the driver or passenger seat, as this could wake her up.
9. Connect the harness and wake your vehicle.
10. You should not need to perform a hazard reset.
11. Connect your Comma and off you go!

If you encounter an issue with Driver+ after installation, refer to the Troubleshooting section for assistance.

Harness Install

See the guide and videos in the Hardware Install Guides 
section for detailed instructions.

@mcgaverty—Later model Rivians have a large cable harness to the left of the fuse panel leg.  Removing this bolt and pulling the fuse panel connection out and to the left (so it rests on top of the bolt) will give you more access room in the back.

@mcgaverty—Removing the white connector in front helps with access. You can use a flathead screwdriver to gently push up on the release tab located at the bottom left of the connector, while simultaneously pushing the connector out with the screwdriver.

@Seoras—One tool that was absolutely invaluable was an L-shaped poky stick (official term). Highly recommend having something similar.

@mountainman—Fold the carpet back towards you. You will likely break the styrofoam on the left side, but it still tucks back in fine. That will create much more space. I also think running your left hand behind the [fuse panel] support on the left makes it much easier to guide the plug.

Cable Routing

The Electric Valentines - How to Hide and Route Comma 3X Cables

AmpedUp - Rivian Comma AI Installation Guide shows how to route the USB-C cable at the 5-minute mark.

Carlos Alvarez - The Rivian RADAR detector mirror mount shows how to remove the Mobile Eye housing, allowing you to route the USB-C cable behind it if you feel ambitious.  The retainer clips have been known to break, so be careful.

“Something a lot of people do is forget to remove the piece above the mirror itself first. That can make the top a little harder to get because it's trying to pry against the mirror itself, then they end up popping the mirror off too.” - Tip submitted by@livinginKaos

Mirror housing Clip Locations

If you don't want to remove the A-pillar cover, there is sufficient space to easily push the cable between the windshield and the A-pillar.

A-pillar Clip Locations

@mcgaverty—For cable routing, you can also pop this side panel off. There is an opening to push the cable through to the footwell.

Installing a Power Source

There are two options for installing a power source for your Comma 3X.

Comma Power

1. If you purchased your harness from Comma, use the supplied Comma Power.
2. Connect the OBD-II end to your port in the driver’s footwell.
3. Run the long cable around your center console, tucking it in the gaps.
4. Plug the 4-pin Molex connector end into the Comma harness box.

Fuse Tap

1. If you purchased your harness from Lucas, it now comes with a fuse tap. This keeps your OBD-II port free and simplifies cable management.
2. Unscrew the two Torx T20 screws and remove the passenger footwell cover.  You will see a fuse panel tucked up behind it.
3. Remove the 20-amp fuse in slot F34 (which is for the front and rear center lamps).  Save that fuse as a spare.

4. Plug your fuse tap into F34.  It should have 5 and 20-amp fuses pre-installed. The wire should point out towards the AXM. A tight bend is fine.
5. Plug the 4-pin Molex connector end into the Comma harness box.
6. Tuck in your harness and wires.
7. Reattached the passenger footwell cover.

Disconnecting AXM Power

As of July 2025, Lukas’ harness does not use AXM power and includes a fuse tap.  Skip this section if your harness from Lukas included a fuse tap.

If you have the original harness from Comma or Lukas, it draws power directly from the AXM, which can sometimes cause intermittent ACC, radar, and Driver+ errors. While the exact cause is still unclear, these issues can often be resolved by switching to a cleaner, independent power source.

1. It's easiest if you completely remove the harness from the car, but it should also be doable while it's still installed—just be sure to use the sleep method to ensure no power is running through the harness during the process.
2. Remove the harness box (the component with the USB-C and 4-pin Molex power ports) from the rest of the harness.
3. In the wiring connector that plugs into the harness box, look for two red wires if you have a harness from Comma or two purple wires if you purchased your harness from Lukas. These are the 12V power lines. They’re located side by side in the center of the connector.

Wire Identification

                Comma Harness                                Lukas Harness

4. Use your jeweler’s tool to lift the locking tabs above each wire and gently pull them out of the connector housing. Quick How-To Video.

Locking Tabs & Wago Clamp

5. With both wires removed, insert them into a Wago clamp (or other secure splicing method) to connect them directly to each other. This allows the 12V line to bypass the harness box and the Comma unit, effectively isolating those electronics from AXM power.

Windshield Placement

You’ll need the 8-degree mount, which came with your harness.

@gerrylum— Attach the mount to your windshield about 1” under the center of the mirror, not the whole assembly, since the Mobile Eye assembly is off-center.

Magnetic Mounts for Quick Release

Magnetic mounts allow you to easily remove your Comma 3X from your vehicle, preventing theft and keeping it cool in hot temperatures.  It also allows you to bring the Comma 3X inside to upload routes with Firehose (lots of Gigs!) to the Comma team for training and improvement.  There are several magnetic mounts on the market right now.  Check out Erich Moraga’s youtube channel where he’s reviewed all the mounts and tells you how to get them:

https://www.youtube.com/@ErichMoraga

Attach the Beartech or Chun magmounts to the Comma 3X with the USB-C ports facing the rear of the vehicle, not the windshield. This prevents the wires from passing over the cameras and allows the window mount to be flush against the windshield.

Magnetic Mounts + Longitudinal Upgrade

The Longitudinal Upgrade Kit uses another USB-C cable that connects directly to the secondary USB-C port in the back of the Comma 3X.  This eliminates the “quick release” functionality of your magnetic mount.  To solve this, we can use a magnetic USB-C adapter between the USB-C port and the USB-C cable.  We must use an extender because the port is recessed into the Comma 3X.

The Secondary USB-C port has a plastic cover that must be removed.

The extender plugs into the port and the magnetic adapter plugs into the extender.

Troubleshooting

Software Installation

It’s best to install the default Openpilot software first to ensure your Comma 3X hardware is set up properly and to familiarize yourself with how Openpilot assists your driving.

We’ve encountered instances of software downloads stalling due to a home mesh network.  If this happens, try using a mobile hotspot or your Connect+ connection.

Hardware Installation

If, after installing your Comma 3X, you have no power to the unit or are seeing error lights on the driver display screen, try the troubleshooting procedures below. After each procedure, check to see if your Comma is operating properly.  You may not need to complete all three.

1. Perform a Hazard Reset

1. Hold down the left-most steering wheel button and the hazard button above the mirror until your Rivian's displays turn off.
2. This software reset will take under 10 minutes.
3. Avoid a second reset within an hour.

2. Allow the Rivian to Deep Sleep

1. Shut all doors and lock your Rivian.
2. Step away from the vehicle and keep all phones and key fobs out of range for at least 30 minutes.
3. This allows all modules to power down completely.

3. Perform a High Voltage Reset

1. Note that this is an advanced procedure.  If you do not feel comfortable executing this, contact Rivian service.
2. Open your driver’s side window and leave the driver’s door ajar.  You’ll be cutting all power to the vehicle, so you don’t want to get locked out.
3. Open your hood and remove the air intake cover.

4. Disconnect the fireman’s loop connector by pressing the release tab and pulling on the loop.  This cuts power to your high-voltage battery.  
   Do not cut the loop!

5. Disconnect the negative 12V battery terminal cable(s).  
   (Early model Rivians have two 12V batteries.)
6. Let the vehicle rest for at least 30 minutes.
7. Reattach the negative battery terminal(s).  If you have two 12V batteries, reconnect them in sequence as quickly as possible.
8. Reattach the fireman’s loop connector and the air intake cover.
9. Wake your Rivian and perform a Hazard Reset.

Operation

1. If you experience power issues or communication errors during operation, ensure that Comma Power is installed.
2. Ensure you are using a high-quality USB-C 3.1 Gen 2 or 3.2 cable like this one:  PDEEY USB-C 3.2 Gen 2.
3. Some drivers have had success flipping their USB-C cable connectors 180 degrees.
4. You can also try the troubleshooting steps above to restore your Comma to Rivian connection.
5. If your Comma powers on, but does not engage the camera when pressing the brake to put the Rivian into “Drive”, ensure the OBD-C cable is plugged all the way into the Comma 3X.  You will hear and feel an audible click when the cable is fully inserted. If it’s not fully inserted, you may get power to the Comma 3X, but not data.

Other Resources

• OpenPilot Wiki - Troubleshooting

• Github repo for more complex communication issues and fixes

• Unofficial Documentation of Unofficial Fixes

• Github repo for hardware issues and fixes

• Comma Connect Tutorial

• explains how to set up Comma Connect, upload logs, and share routes

Comma Connect

Set up Your Account and Share Routes

• Comma Connect Tutorial

Create and Share Clips

• Comma Connect Clips Tutorial

Sunnypilot

Installation

It’s best to install standard Openpilot first to ensure your Comma 3X hardware is set up properly and to familiarize yourself with how Openpilot assists your driving.

Once you have some Openpilot miles under your belt, sunnypilot is a community- supported fork (version) that allows you to utilize Openpilot’s longitudinal control and MADS.  Currently, Openpilot still uses Rivian’s ACC.

1. Before starting this process, it’s best to bring your Comma 3X inside and power it with a USB-PD or laptop charger on your home’s WiFi.
2. Reset your Comma 3X by going to Settings > Software > Uninstall Openpilot.
3. Your Comma will reboot.
4. Choose “Custom Software” and type in sunnypilot/staging.
5. Connect your Comma 3X to your Rivian and allow it a minute or two to Register and Fingerprint. This process detects and selects your Rivian under the Vehicle menu.
6. If you have the Longitudinal Harness Upgrade installed, your Comma 3X will automatically detect it once connected to your Rivian.
7. Toggle ON Openpilot longitudinal by going to Developer > openpilot Longitudinal Control (Alpha). 
8. You'll know if Openpilot Long is working if you see a speed limit sign in the upper left corner of your Comma 3X when you engage.
9. If not, you may need to reboot your Comma 3X so it detects the additional Panda installed.

As of 07 June 2025, the xnor development and testing branches from Lukas
(Rivian port’s lead developer) have been merged into the official sunnypilot build!  

Discord release message here.  

You can install…

• sunnypilot/staging
• sunnypilot/master (uncompiled, so will take time to load)

Version Comparison Table

 * If MADS is enabled, otherwise, n/a
** Automatic lane change with Blind Spot Monitor detection

 *** Driving Personality also adjusts Follow Distance

 * Manual Cruise Control (only available when towing)

Glossary

ADAS (Advanced Driver Assistance System)

• Technologies that assist drivers with the safe operation of a vehicle
• Comma is a Level 2 ADAS, which means it can control steering, acceleration and deceleration; but the driver must remain engaged and ready to take over at any time.

Driving Model

• The machine-learning “brain” of Openpilot — a neural-network file that ingests camera, radar, and vehicle-state data and outputs the desired path plus steering, acceleration, and braking targets.
• On Sunnypilot, you can experiment with different driving models by clicking on the Models menu.  You’ll need to select and download each one.  You do not need to recalibrate when changing driving models.
• Favorite models for Rivian drivers include: Tomb Raider 7, Tomb Raider 10, WD40, and Down to Ride.

Fork

• A new, independent software project created by copying and modifying the source code of an existing one.  Sunnypilot is a fork of Openpilot.

MADS (Modified Assistive Driving Safety)

• Available on Sunnypilot.  Utilizes ALC (Automatic Lane Centering) while allowing you, the driver, to control speed, acceleration, and braking.  Many drivers find it very useful on side streets and in heavy stop-and-go traffic.
• MADS in Action: Sunnypilot MADS on Rivian

Longitudinal (LONG) Control is forward speed and braking

• Rivian stock version is ACC (Adaptive Cruise Control)

Lateral (LAT) Control is left and right steering

• Rivian stock version is LKAS (Lane Keep Assist System)