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.
Technic Pin Double with Axle HoleLight Bluish GrayPart 32138Element 4211888×4
Technic Pin without Friction Ridges LengthwiseLight Bluish GrayPart 3673Element 4211807 or 36731941 spare in the box×4
Technic Wedge Belt Wheel [aka Pulley]Light Bluish GrayPart 4185Element 6321743 or 4494222×3
Technic Worm Gear Type 2Light Bluish GrayPart 32905Element 6185471×2
Wheel 11 x 8 with Center GrooveLight Bluish GrayPart 42610Element 4211758×4
Blue
66 pieces
Technic Axle Pin with Friction Ridges LengthwiseBluePart 43093Element 4309323 or 4206482×28
Technic Pin Long with Friction Ridges Lengthwise, 2 Center SlotsBluePart 6558Element 4514553×38
White
24 pieces
Control Unit, IR-Beacon / Remote Handset, EV3WhitePart 72156Element 6127283 or 6093253×1
Hub, EV3 Brick [Complete Assembly]WhitePart 95646c01Element 6261688 or 6187080×1
Technic Panel Car Mudguard LeftWhitePart 61071Element 6015597 or 4540101×1
Technic Panel Car Mudguard RightWhitePart 61070Element 6015596 or 4540100×1
Technic Panel Fairing # 3 Small Smooth Long, Side AWhitePart 64683Element 4547581×3
Technic Panel Fairing # 4 Small Smooth Long, Side BWhitePart 64391Element 4547582×3
Technic Panel Fairing #5 Long Smooth, Side AWhitePart 64681Element 4558802×3
Technic Panel Fairing #6 Long Smooth, Side BWhitePart 64393Element 4558797×3
Technic Tooth 1 x 3 with Axle Hole [Rounded Underside]WhitePart 41669Element 4173941×4
Wing / Blade 1 x 4 with Pin HoleWhitePart 98347Element 4656205×4
Dark Bluish Gray
14 pieces
Technic Axle 4 with StopDark Bluish GrayPart 87083Element 6083620 or 4560177×4
Technic Axle 5.5 with Stop [Rounded Short End]Dark Bluish GrayPart 59426Element 4508553×2
Technic Axle 8 with StopDark Bluish GrayPart 55013Element 4499858×6
Technic Gear 24 Tooth [New Style with Single Axle Hole]Dark Bluish GrayPart 3648bElement 6133119 or 4514558×2
Yellow
11 pieces
Technic Bush 1/2 Smooth with Axle Hole Semi-ReducedYellowPart 32123bElement 6271167 or 32123241 spare in the box×11
Tan
9 pieces
Technic Axle 4 with Centre StopTanPart 99008Element 4666999×3
Technic Gear 12 Tooth BevelTanPart 6589Element 4565452 or 4514556×1
Technic Gear 20 Tooth BevelTanPart 32198Element 6031962 or 4514557×1
Technic Pin Long without Friction RidgesTanPart 32556×4
Dark Tan
4 pieces
Technic Axle 3 with StudDark TanPart 6587Element 6031821 or 6013821×4
[No Color/Any Color]
1 piece
Sticker Sheet for Set 31313-1[No Color/Any Color]Part 13710Element 6031766×1
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.