I have the weirdest thing with my son's set. Currently one of the yellow action tiles honks the horn but the other yellow brick does not. No matter the lighting conditions, the position, orientation, etc. They both used to work and suddenly one is specifically not reacting. If it was different colors not responding I would assume battery issue is affecting the color sensor, but they are both the same color surface finish. Any thoughts?

  • 1
    Welcome to Bricks.SE! I have this set, but I've not encountered this before. Would I be correct in assuming that you've already tried washing both yellow elements with soap and water?
    – jncraton
    Sep 16, 2019 at 15:38
  • Which train is this about? A set number or link would help. Haven't seen it, I have no clue how it works, but are you sure it's a color sensor and not something lese like NFC which could account for one brick being defective and not the other?
    – Joubarc
    Oct 10, 2019 at 12:22
  • 1
    Nevermind, it IS color-based
    – Joubarc
    Oct 10, 2019 at 12:30

2 Answers 2


You may want to contact the LEGO customer service about it and see if they can provide a replacement brick. Assuming your train is 10874 or 10875, they should still have it in stock and you can probably just order a new one via a replacement part order.

On the other hand, since the recognition appear to be indeed color-based this might not help at all.


It seems the train motor shoots light and detects its reflections to respond to each action bricks. When the surface of the action brick is scratched up, the sensor cannot detect the color properly. This may explain why your toy responds to one yellow and not the other yellow action brick.

Incidentally, I noticed when the battery level is very low, the train fails to respond to any action bricks...

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