Trailer "bulb check" feature

**tact** · 7th January 2026, 06:09 AM

Hi All,

Did a search and saw no posts on this.... In the L663 iGuide there is mention of a bulb check feature that can be activated from the driver interactive screen. Some of the wording:
Before carrying out a bulb check:

Switch off all of the vehicle’s lights.
Apply the Electric Parking Brake (EP.
Switch off the vehicle’s ignition.

The bulb check illuminates all of the vehicle's lights and the corresponding trailer lights in turn. The sequence automatically stops after 3 minutes.
Check that each trailer light illuminates at the same time as the corresponding vehicle light when carrying out either of the operations shown below.
This would be a really useful feature but for the life of me, I cannot get it to work. Anyone tried/succeeded? Wondering if it is dependant on specific feature/pack being added to the vehicle? e.g. I don't see any mention of this as a feature of the optional Towing Pack (which I do not have with my 110 D250 S). Also cannot see any reference to it in google searches.

**grey_ghost** · 8th January 2026, 02:27 PM

Hi,

I haven't heard of this feature either to be honest - but I'm guessing that you would need the optional tow pack for it to work?

Sorry - I'm not much help.

Cheers,
GG.

**WhatIsClocks** · 11th January 2026, 02:47 PM

https://youtu.be/upUqHBR6ISw?t=64 will probably answer your question -- there's a button in the luggage area and requires the ignition to be off.

**tact** · 12th January 2026, 05:50 PM

Originally Posted by WhatIsClocks

https://youtu.be/upUqHBR6ISw?t=64 will probably answer your question -- there's a button in the luggage area and requires the ignition to be off.

Hey thanks. The iGuide mentions buttons in the load area AND a process to follow to do it on the interactive screen. My vehicle does not have the buttons in the back for this. So looking for what is needed to get it to work using the screen up front.

Have been thinking that maybe the buttons in the back only come if ordering some pack or other for new builds.

I can see the Trailer Module is physically installed in my car (it is under the load area floor) but I also see it is marked as "not fitted" in the vehicle configs (via the GAP tool). So it's possible there is just a config that needs turning on to get the bulb check feature to work. (This worked for other devices, like the subwoofer, physically present, just needed to enable it in the vehicle config using the GAP tool)

**jwb** · 14th January 2026, 10:46 AM

I have the factory tow pack installed. There are 2 buttons in the cargo area for raising and lowering the rear to aid un/hitch and very helpful they are.
Looks like UK models have 2 buttons 1 for deploying the hitch and the other for bulb check so thinking our AU models don't get the bulb check.

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