A GMC VIN starts with 1GT on US-built trucks (Sierra and Sierra HD patterns we tested) and 1GK on US-built SUVs and crossovers (Yukon, Yukon XL, Acadia, Terrain). Canada Terrain patterns we tested used 2GK, and some Mexico Terrain patterns used 3GK. Positions 4-8 carry the line, series, body and engine, 9 is the check digit, 10 is the model year, and 11 is the plant. A clean decode only describes the factory build, so run recalls and a history report before you write a check.
We ran GMC patterns through NHTSA's free vPIC decoder in mid October 2026 because Sierra and Yukon listings keep borrowing Chevy talk. GMC shares platforms with Chevrolet -- Sierra with Silverado, Yukon with Tahoe, Terrain with Equinox -- but the WMI and trim labels are not interchangeable. For the general 17-character walkthrough, use our how to decode a VIN guide. The Chevy side lives in our Chevrolet VIN decoder. This page sticks to what GMC VINs actually returned.
Positions 1-3: 1GT trucks vs 1GK SUVs
vPIC lists General Motors LLC behind every GMC pattern we tried. The useful split is vehicle type. A 2020 Sierra 1500 pattern starting 1GTU9DED came back as a Fort Wayne, Indiana pickup with a 5.3-liter L84. A 2020 Elevation pattern starting 1GTR9CEH returned a 4.3-liter LV3 at the same plant. A 2021 Sierra 2500 Denali starting 1GT49REY decoded to Flint, Michigan with a 6.6-liter L5P Duramax. So if a seller calls a truck "Mexicali-built" and the plant field says Fort Wayne or Flint, believe the VIN.
On the SUV side, a 2021 Yukon SLT pattern starting 1GKS2BKD came back Arlington, Texas with a 5.3-liter L84. A Yukon XL pattern starting 1GKS2GKC also pointed at Arlington. A 2017 Acadia SLT starting 1GKKNMLS returned Spring Hill, Tennessee with a 3.6-liter LGX. Terrain is the crossover that moves plants: a 2016 Denali pattern starting 2GKFLVEK decoded to CAMI in Ontario with a 2.4-liter LEA, and a 2019 SLT pattern starting 3GKALVEG came back San Luis Potosi, Mexico. Same nameplate, different country. Match the dash plate, door-jamb label and title the way we describe in how to find and verify a VIN.
Positions 4-8: shared platforms, different badges
GMC packs model line, series, body, drive and engine into the middle five characters, and vPIC reads them back as Model, Series, Trim and Engine Model. The engine label is the one that matters for recalls. Our Sierra 1500 tests returned L84 for the 5.3 and LV3 for the 4.3. Heavy-duty patterns returned L5P for the Duramax 6.6. Acadia returned LGX for the 3.6. Terrain returned LEA for the older 2.4. Those same RPO-style engine codes show up on Chevrolet twins, which is why a Sierra decode and a Silverado decode can look almost identical once you get past the WMI.
Honestly, skip forum letter charts. Trim strings in vPIC often list several packages on one pattern, and that is normal. Paste all 17 characters, then compare the result with the window sticker or the glovebox SPID / door-pillar QR data if the truck still has it. GM moved a lot of that content into a QR code on the certification label for 2018-and-newer vehicles, which our Chevrolet decoder covers in more detail. If the listing says Denali and the decode says Fleet/Base, you have a conversation to start.
Positions 9, 10 and 11: check digit, year, plant
Position 9 is the check digit defined in 49 CFR 565.15. A typo usually fails the math. A cloned VIN copied off a real truck passes it, so treat a valid check digit as the minimum bar. Position 10 is the model year letter (L was 2020, M was 2021, P was 2023 in our runs). Position 11 is the plant: Fort Wayne and Flint showed up on Sierras, Arlington on Yukons, Spring Hill on Acadias, CAMI and San Luis Potosi on Terrains.
After the decode: Sierra vs Silverado, recalls, history
If you are shopping a used Sierra, read our used Chevy Silverado buying guide for the shared powertrain homework, then confirm the exact VIN on GM's recall lookup. GM's May 2025 recall report 25V274 covers a large group of 2021-2024 trucks and SUVs with the 6.2-liter L87 V8 for engine failure that can cause loss of propulsion. That campaign is VIN-specific, so do not assume a Sierra is in or out because a Silverado friend had the same year. Older GM ignition-switch history still turns up on older used lots; our GM ignition switch recall used-car check explains what to look for on paper.
Car and Driver's Sierra 1500 page is useful for generation context, and IIHS Sierra ratings change by year and cab style, so check the exact one. None of this shows salvage brands, auction damage, odometer gaps or old insurance claims. Those come from DMV, insurer, auction and shop records, which is what CARFAX describes as the basis of its reports. Pull your own report; seller-supplied PDFs still get edited. As of mid October 2026, a CARFAX report through us is about $5.50 as a guest or about $4.50 as a member, and a CARFAX plus AutoCheck bundle is about $6.75, against roughly $39.99 to $44.99 at retail. Confirm at checkout. We are a licensed CARFAX and AutoCheck reseller, not affiliated with CARFAX, AutoCheck, or Experian.
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