Rule out the usual hiding places first. If the piece really is gone, check the set piece by piece
and leave with the element ID LEGO asks for, or a link to buy the part.
Builders who report a missing piece often find it in one of these places. Tick each one off as you look.
Look-alike colors in this set
These parts appear in this set in two colors that are easy to confuse. If you are one short in one color,
check whether it went in where the other color belongs. Each color has its own element ID in the parts list
at the back of the instructions.
Technic Axle and Pin Connector PerpendicularBlack ×14Dark Bluish Gray ×2Black is darker than Dark Bluish Gray.
Technic Beam 1 x 2 Thick with Pin Hole and Axle HoleBlack ×8Dark Bluish Gray ×4Black is darker than Dark Bluish Gray.
Technic Beam 1 x 3 ThickBlack ×7Dark Bluish Gray ×2Black is darker than Dark Bluish Gray.
Technic Beam 1 x 5 ThickBlack ×5Dark Bluish Gray ×1Black is darker than Dark Bluish Gray.
Technic Beam 1 x 5 Thin with Axle Holes on EndsBlack ×14Dark Bluish Gray ×1Black is darker than Dark Bluish Gray.
Technic Beam 1 x 7 Thick with Alternating HolesBlack ×5Dark Bluish Gray ×2Black is darker than Dark Bluish Gray.
2 more look-alike pairs
Technic Driving Ring Connector Smooth [2 rounded and 2 flat side walls]Black ×2Dark Bluish Gray ×4Black is darker than Dark Bluish Gray.
Technic Pin Connector Hub with 1 Pin with Friction Ridges Lengthwise [Centered Friction Ridge]Black ×8Dark Bluish Gray ×2Black is darker than Dark Bluish Gray.
Technic Steering Hub for Portal AxleDark Bluish GrayPart 92909Element 4610378×4
Tile Round 1 x 1Dark Bluish GrayPart 98138Element 6284596 or 62224161 spare in the box×1
Yellow
21 pieces
Technic Axle 3YellowPart 4519Element 6130007×3
Technic Axle 5YellowPart 32073Element 6130008×2
Technic Axle 9YellowPart 60485Element 6130010×1
Technic Axle and Pin Connector Perpendicular 3L with 2 Pin HolesYellowPart 42003Element 6273711 or 4200324×2
Technic Bush 1/2 Smooth with Axle Hole Semi-ReducedYellowPart 32123bElement 6271167 or 32123241 spare in the box×1
Technic Engine CrankshaftYellowPart 2853Element 6640378 or 4119474×2
Technic Engine Piston RoundYellowPart 2851Element 4112203 or 285124×6
Technic Pin Connector Hub with 1 Pin with Friction Ridges Lengthwise [Centered Friction Ridge]YellowPart 65487Element 6282151×4
Reddish Brown
15 pieces
Technic Axle 3 with StopReddish BrownPart 24316Element 6135494×7
Technic Axle 5 with StopReddish BrownPart 15462Element 6159763×8
Tan
14 pieces
Technic Engine Crankshaft CenterTanPart 2854Element 6355727 or 6013937×2
Technic Gear 12 Tooth BevelTanPart 6589Element 4565452 or 4514556×5
Technic Gear 20 Tooth Double Bevel with Axle Hole Type 1 [+ Opening]TanPart 18575Element 6346517 or 6084724×3
Technic Pin 3/4TanPart 32002Element 6663097 or 60139381 spare in the box×2
Technic Pin Long without Friction Ridges, with Anti-Roll NotchTanPart 39888Element 6321305×2
Orange
11 pieces
Technic Beam 1 x 2 Thick with Pin Hole and Axle HoleOrangePart 60483Element 6265128 or 6057526×6
Technic Pin Connector Round 1L [Beam]OrangePart 18654Element 63903801 spare in the box×2
Technic Pin Long with Friction Ridges Lengthwise and Stop Bush [2 Lateral Holes, Small Pin Hole]OrangePart 65304Element 6347790×3
Trans-Clear
6 pieces
Technic Engine Cylinder without Side Slots, with Bottom SlotsTrans-ClearPart 2850bElement 6514435 or 6353017×6
White
6 pieces
Technic Axle and Pin Connector Perpendicular 3L with Centre Pin HoleWhitePart 32184Element 6276981 or 6114940×2
Technic Pin Connector Round [Slotted]WhitePart 62462Element 6550164 or 6173116×4
Flat Silver
5 pieces
Technic Pin Connector Round [Slotted]Flat SilverPart 62462Element 6245499 or 6054858×5
Bright Green
4 pieces
Plate Special Round 2 x 2 with Center Stud (Jumper Plate)Bright GreenPart 18674Element 6380676×4
Dark Tan
4 pieces
Technic Axle 3 with StudDark TanPart 6587Element 6031821 or 6013821×4
Dark Turquoise
2 pieces
Technic Beam 1 x 3 ThinDark TurquoisePart 6632Element 6481482 or 4111952×2
Trans-Red
2 pieces
Tile Round 1 x 1 Half CircleTrans-RedPart 24246Element 6507960 or 62640331 spare in the box×2
[No Color/Any Color]
2 pieces
Sticker Sheet 1 for Set 42171-1[No Color/Any Color]Part 10105327Element 6462840×1
Sticker Sheet 2 for Set 42171-1[No Color/Any Color]Part 10107470Element 6478964×1
Tick each piece as you find it, or mark it missing.
When a piece really is missing
Ask LEGO
LEGO takes requests for pieces missing from a new set through its customer service site. The form asks for
the set number and each piece's element ID, the number printed beside the piece in the parts list at the back
of the instructions. This checker lists both.
Mark a piece missing and your list links it to an eBay search for that part, which also covers pieces from
older or second-hand sets.
Keep a record
Copy or download your missing list (the CSV opens in any spreadsheet), or print the whole checklist and tick
pieces off on paper. Your marks stay in this browser, so you can check a big set over several sittings.