Comma 4 - can't get longitudinal enabled with lukas longitudinal harness

[upalikaru]

Hello all,

I have a new Comma 4 with the Comma Rivian harness. I also bought and installed the Lukas longitudinal harness and the Janquick Quick Release Mount.

After installing Sunnypilot, I'm able to get Openpilot lateral working. But I'm not able to get longitudinal working, similar to https://www.rivianforums.com/forum/...-help-longitudinal-control-not-working.57285/

I don't see the option to enable Alpha Longitudinal in the Developer settings menu on the Comma 4. I also tried toggle Alpha Longitudinal using Sunnylink, but it also doesn't seem to stick. It keeps resetting back to Disabled. And even then, I don't think it's activating (Rivian TACC is being used instead)

Based on the comment by Gerry in that thread, it looks like the long harness is supposed to show some kind of LED in blue/red, but mine doesn't show any LED. Is there something wrong with my install, or is my longitudinal harness defective?

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[godfodder0901]

Hello all,

I have a new Comma 4 with the Comma Rivian harness. I also bought and installed the Lukas longitudinal harness and the Janquick Quick Release Mount.

After installing Sunnypilot, I'm able to get Openpilot lateral working. But I'm not able to get longitudinal working, similar to https://www.rivianforums.com/forum/...-help-longitudinal-control-not-working.57285/

I don't see the option to enable Alpha Longitudinal in the Developer settings menu on the Comma 4. I also tried toggle Alpha Longitudinal using Sunnylink, but it also doesn't seem to stick. It keeps resetting back to Disabled. And even then, I don't think it's activating (Rivian TACC is being used instead)

Based on the comment by Gerry in that thread, it looks like the long harness is supposed to show some kind of LED in blue/red, but mine doesn't show any LED. Is there something wrong with my install, or is my longitudinal harness defective?

Rotate the USB-C 180 degrees.

 

[upalikaru]

Thanks for the reply. Which USB-C connection?

 

[godfodder0901]

Thanks for the reply. Which USB-C connection?

The Aux. Either end.

 

[upalikaru]

Are you referring to the short USB-C cable in the photo labeled in yellow "Lukas Long"? If so, I tried reversing it from both sides (one side at a time) and no luck. Still no LED on the box.

 

[upalikaru]

Adding one more photo to show connection to vehicle side

 

[godfodder0901]

Are you referring to the short USB-C cable in the photo labeled in yellow "Lukas Long"? If so, I tried reversing it from both sides (one side at a time) and no luck. Still no LED on the box.

Looks like you need to enable Alpha on the device itself, like the thread you referenced. It doesn't sound like it takes when done through Sunnylink.

 

[upalikaru]

I don't see the option to enable Alpha Longitudinal in the Developer settings menu on the Comma 4. Is it because Sunnypilot is not detecting the long harness?

 

[jrmbadger]

Im unfamiliar with the specific Janquick mount. Is this the one you are using? Mount If so, if you look at the diagram there, there is a “data blocker” usb thing on the end of the usb connection that then gets connected to the lukas harness. That doesnt seem to be plugged in in your case.

Not sure what that does but could that be the issue?

If not, id try connecting everything without the usb combiner thingy supplied with the mount. Just run the two usb cables up to the comma 4 ports. Not getting any lights on the lukas box indicates a lack of power likely.

 

[upalikaru]

Yes, that is the Janquick mount I have, specifically the Comma 4 version.

Mine didn't come with the "data blocker" plug. According to the "update" tab, it seems to be included with a newer version of the mount?

Updated: March 25, 2026

Due to Comma’s removal of USB support for Panda
( https://github.com/commaai/openpilot/pull/37217/changes )
we have made the following updates to the included accessories:

1. Removed the connecting cable between the secondary port of the Comma device and the mount.
2. Revised the PCB board of the mount and removed the secondary USB port.
3. Added a Data Blocker for connection to the Lukas Box.

 

[jrmbadger]

Try it without the mount and see if you can get it working. If you can get it working without the mount, then contact Janquick and see what they recommend.

 

[upalikaru]

I tried it with the 2 separate usb-c cables going to the Comma 4 and no luck. I still don't see any LEDs turned on on the long harness box.

 

[jrmbadger]

Hmmm. The light on the lukas box is very small. Are you sure you don’t see it?

also, try and turn the cable going into the comma 180 degrees.

if that doesn't work i would see if @gerrylum or @LivingInKaos have ideas. Otherwise perhaps the longitudinal harness is bad.

 

[LivingInKaos]

So just to be sure here. You have the main odb USB c going from the harness to the mount which then connects to the main port on the comma. Then you have also placed a USB c cable from the longitudinal adapter and the auxiliary port on the comma?

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