2021 GMC Sierra 3500HD
The 2021 GMC Sierra 3500HD is a pickup truck; vehicles over 8,500 lb GVWR are not certified for fuel economy by the EPA, so this page is built from NHTSA's recall, complaint and investigation records. NHTSA lists 5 recall campaigns for this model year, 2 rated critical, which gives it a Safety Signal grade of F. Owners have filed 20 complaints, most often about the power train.

Specs & fuel economy
Source: EPA fueleconomy.govNo EPA fuel-economy record: the EPA does not certify vehicles over 8,500 lb GVWR. Recall, complaint and investigation data below come from NHTSA.
Specifications filed with NHTSA
Source: NHTSA vPICDimensions Exterior
| Body style | Incomplete - Chassis Cab (Double Cab) |
| Doors | 4 |
| GVWR class | Class 3: 10,001 - 14,000 lb (4,536 - 6,350 kg) |
Engine Basics
| Cylinders | 8 |
| Displacement | 6.6 L |
| Engine configuration | V-Shaped |
Fuel Economy
| Fuel | Gasoline |
Transmission
| Drivetrain | 4WD/4-Wheel Drive/4x4 |
Filed by the manufacturer with NHTSA under the federal vehicle-identification rule and decoded from the VIN pattern — not a manufacturer press kit, so it describes the configurations we could identify rather than every trim (seen: AT4, Fleet/Base, SLE, SLT). Figures for the trim you are looking at may differ.
Dimensions & weight
Source: Transport Canada| Length | 235.4–266.1 in |
| Width (body, without mirrors) | 81.9 in |
| Height | 79.9–80.7 in |
| Wheelbase | 141.7–172.0 in |
| Track, front | 67.3 in |
| Track, rear | 68.1 in |
| Curb weight | 6,338–7,172 lb |
| Weight distribution, front/rear | 57/43 |
Measured by Transport Canada for its Canadian Vehicle Specifications database, which covers the North American versions of each model — here 14 configurations: Crew Cab L/Box Drw 2WD, Crew Cab L/Box Drw 4X4, Crew Cab L/Box Srw 2WD, Crew Cab L/Box Srw 4X4, Crew Cab M/Box 2WD, Crew Cab M/Box 4X4 …. Where a range is shown, those versions differ. Width is the body without mirrors, which is why it can read narrower than a brochure figure. Before we used it we checked it against the US manufacturer press kits we hold (27 Sep 2026): wheelbase agreed within 1% on every vehicle we could compare, length on 98%, and the curb weight fell inside the manufacturer's range on 96%. Source dataset. Contains information licensed under the Open Government Licence – Canada. Licence.
Factory warranty running out?
The 2021 GMC Sierra 3500HD is in the years where transmission, electronics and drivetrain repairs land on the owner. What an extended plan does and does not cover is worth reading before a dealer quotes you one.
What to check before you buy →Affiliate disclosure: some links on this page are affiliate links. If you request a quote or buy through them we may earn a commission at no extra cost to you. Nothing on this page changes because of it.
Recalls (5)
Source: NHTSA recall databaseLatches/Locks/Linkages
N232426400Service Brakes, Hydraulic
N212349181Seat Belts
N202322230Seat Belts
N202314670These are vehicle campaigns — the ones the automaker filed against this model. NHTSA also records equipment recalls, filed by a parts maker against a component (a tyre, a child seat, an aftermarket part), and those are not listed here or counted above. nhtsa.gov/recalls shows both for a VIN.
NHTSA defect investigations
Air Bags:Srs Malfunction Warning Lamp/Light — Air Bag Malfunction closed
On April 9, 2021, the Office of Defects Investigations (ODI) opened PE21-010 to investigate instances of air bag malfunction indicator light (MIL) illumination and potential for frontal air bag non-deployment in several vehicles manufactured by General Motors (GM). The vehicles included model year (MY) 2020 through 2021 CT4 and CT5 passenger cars, Sierra and Silverado trucks (1500/2500/3500 models), XT4 and MY 2021 Escalade, Suburban, Tahoe, Yukon SUVs. Technical Service Bulletin (TSB) 21-NA-005, issued in March 2021, addresses air bag MIL illumination with diagnostic trouble codes (DTCs) B0001-1B or B0012-0D. It cites rust particles in the connection terminal interface of the driver air bag
Opened Apr 9, 2021 · closed Aug 24, 2023 · action PE21010 · the investigation’s page →
Whether any of this applies to one specific Sierra 3500HD
A campaign covers a build range, not a model year, so two identical-looking cars from 2021 can differ. Both of these check a VIN against the manufacturer’s own list, free, in about ten seconds. GMC publishes its own lookup because federal rule 49 CFR 573.15 requires it to, and to keep it current to within seven days.
Hear about a recall before the letter does
The manufacturer’s letter is the last step of a recall: it has up to 60 days after filing to mail owners, at the address on the registration. We email you the day NHTSA posts a recall on the 2021 GMC Sierra 3500HD, with what to do next. Nothing else, ever — no newsletter, no marketing, one-click unsubscribe in every message.
Parts & accessories for the 2021 GMC Sierra 3500HD
Search by fitment on eBay Motors — OEM take-offs, aftermarket, and the trim pieces dealers no longer stock. The listing and the price are the seller's.
Find parts for this Sierra 3500HD →Owner complaints
Source: NHTSA complaint database0 involved a crash · 0 a fire · 0 injuries · 0 deaths reported
10 per 10,000 built · GMC reported 19,358 Sierra 3500HD built (its Early Warning production report to NHTSA)
Filed per year: 2021: 2 · 2022: 5 · 2023: 1 · 2024: 3 · 2025: 8 · 2026: 1
Most-cited components
In owners' own words
Filed with NHTSA by the people who own these cars, one per problem area. Quoted as written, with anything identifying removed.
The contact filed the complaint on behalf of the owner of a 2021 GMC Sierra 3500. The contact stated that while the vehicle owner was driving at an undisclosed speed, the driver noticed that the rear wheels were attempting to lockup. The contact stated that the failure was noticeable while driving forward and while reversing.
During takeoff the transmission acted as if it was in neutral while I was crossing traffic luckily, the semi truck that was coming towards me was able to stop. I had the vehicle towed to a shop. After the vehicle was towed to the shop the transmission acted normal when the mechanic searched the VIN number.
The contact owns a 2021 GMC Sierra 3500. The contact stated that while his wife had the vehicle idling with the rear defroster activated, shortly afterwards, she observed smoke coming from the plastic on the rear sliding window.
The contact owns a 2021 GMC Sierra 3500. The contact stated that while reversing, the back over prevention camera screen displayed an image of the ground. The contact stated that the image was approximately ten feet behind the vehicle. The vehicle was taken to the dealer; however, the failure was not duplicated.
Multiple instances of diesel engine emissions system parts and software failure. While driving, towing or not, the DIC would randomly display a message that the DEF level is low and reduced speed will occur in x-amount of miles and that mileage would then begin a visible countdown on the DIC, sometimes much more quickly than the actual…
The right rear tire (Goodyear Wrangler 275/65R20) separated and blew out on the highway, the truck was very difficult to control however it was safely stopped and there were no injuries. There was no observed warning prior to the blow out. The tire separation caused damage to the right rear quarter panel.
Complaint counts are raw owner reports to NHTSA, not verified defects, and scale with how many were sold. Use them to spot patterns, not to rank.
Reported by GMC itself: 4 death-or-injury claims on this model year in its quarterly Early Warning reports to NHTSA (49 CFR 579.21): 8 injured, as claimed, not verified — about 21 per 100,000 built. Every Sierra 3500HD model year, by year and system → Dated and by system, they are exhibit F of the defect dossier.
Crash ratings
Source: NHTSA NCAPNHTSA has not published 5-Star crash ratings for this model year.
Service bulletins & campaigns
Source: NHTSA manufacturer communications- Term not in NHTSA’s summary · GM warranty extension 22-NA-244This warranty administration service bulletin provides information about GM Accessories - Dealer-Installed, Repaired or Replaced During Warranty Coverage Period.
- 15 years or 150,000 miles, whichever comes first · GM service campaign N242454441-02Certain vehicles listed above, may have a condition where the transmission control valve has worn, resulting in a gradual loss of pressure within the valve.
- 15 years or 150,000 miles, whichever comes first · GM service campaign N242454441-01Certain vehicles listed above, may have a condition where the transmission control valve has worn, resulting in a gradual loss of pressure within the valve.
- 15 years or 150,000 miles, whichever comes first · GM bulletin N242454441Certain vehicles listed above, may have a condition where the transmission control valve has worn, resulting in a gradual loss of pressure within the valve.
The term and the vehicles it covers are the manufacturer’s, as NHTSA’s summary of each filing states them; a dealer checks one particular car by its VIN. Every GM warranty extension (33) → · Every warranty extension on file, all makes →
Most often about: Engine, Electrical System, Equipment, Unknown Or Other, Power Train.
- PIT5698F Service bulletin2026-09-26 · Unknown Or Other
- This PI provides Diagnostics tips on how the LIN bus works and how to diagnosis it.
- PIP4902W Service bulletin2026-09-04 · Unknown Or Other
- This preliminary information advises a dealer on how to email GDS2 session logs into Technical Assistance.
- PIP6127A Service bulletin2026-08-27 · Unknown Or Other
- This document assists GM dealer technicians with diagnosing torque converter concerns to ensure torque converter replacement is necessary. The torque converter part number will be placed on order restriction, and the technician will be asked to follow 25-NA-148 before requesting a part through PQC.
- PIC6551C Service bulletin2026-08-20 · Unknown Or Other
- This Preliminary information communicates to dealer to perform a MEC reset for wireless projection issues
- PIT6031B Service bulletin2026-08-07 · Unknown Or Other
- This Preliminary information communicates an issue where an aftermarket autostop device or rear taillights is causing a dead battery.
- PIT5680B Service bulletin2026-07-23 · Unknown Or Other
- This PI provides information to repair the door water deflector which is not sealed properly allows water into the door jam/sill area.
- PIT5099J Service bulletin2026-07-21 · Unknown Or Other
- PI to help diagnose A/C concern
- PIT5509N Service bulletin2026-07-21 · Unknown Or Other
- This PI provides diagnostic tips for diagnosing electric trailer brakes issues.
A service bulletin is the manufacturer telling its dealers how to diagnose or repair a known condition. It is not a recall, not a finding that the vehicle is defective, and the work is not automatically free — though a bulletin is often what a dealer works from when you describe a symptom, so quoting the document number can save a diagnosis. The count is every communication filed; the list shows the most recent, one entry per campaign, because a single campaign is usually filed as several documents on the same day. The summaries are NHTSA's; the full documents come from the manufacturer.
Diagnostic trouble codes on file
Source: NHTSA manufacturer communications and complaintsCodes documented against this model year in the federal record. A code appearing here does not mean this vehicle will set it — it means the code is part of this nameplate-year's documented history.
| Code | What it means | Most often filed under | Where it appears |
|---|---|---|---|
| P12A6 P12A6 on GMC → | Manufacturer-defined — the meaning is set by the automaker, not the standard. | Engine | 7 bulletins |
| P0442 P0442 on GMC → | A small leak in the evaporative emissions system. | Engine · Gas cap → | 6 bulletins |
| P0455 P0455 on GMC → | A large leak in the evaporative emissions system — often a fuel cap left off. | Engine · Gas cap → | 6 bulletins |
| P0747 P0747 on GMC → | Manufacturer-defined — the meaning is set by the automaker, not the standard. | Power Train | 6 bulletins |
| P0446 P0446 on GMC → | A fault in the evaporative vent control circuit. | Engine · EVAP vent valve → | 5 bulletins |
| P0449 P0449 on GMC → | A fault in the evaporative vent valve or solenoid circuit. | Engine · EVAP vent valve → | 5 bulletins |
| P062B P062B on GMC → | Manufacturer-defined — the meaning is set by the automaker, not the standard. | Unknown Or Other | 5 bulletins |
| P2463 P2463 on GMC → | Soot has built up in the diesel particulate filter beyond the allowed limit. | Engine | 4 bulletins |
| B2B0D B2B0D on GMC → | Manufacturer-defined — the meaning is set by the automaker, not the standard. | Electrical System · Battery → | 3 bulletins |
| B2B0E B2B0E on GMC → | Manufacturer-defined — the meaning is set by the automaker, not the standard. | Electrical System · Battery → | 3 bulletins |
| P0300 P0300 on GMC → | Misfire detected, but not isolated to one cylinder. | Engine · Ignition coils → | 3 bulletins |
| P2714 P2714 on GMC → | Manufacturer-defined — the meaning is set by the automaker, not the standard. | Unknown Or Other | 3 bulletins |
Generic codes (the second character is 0 or 2) mean the same thing on every vehicle sold in the United States. Manufacturer-specific codes (1 or 3) mean whatever the automaker assigned, and no honest source can define them for you — which is why the ones here carry the evidence instead of a definition. A code is a link when enough separate federal documents name it across the catalogue to be worth a page of its own; the rest are listed here, where the vehicle is the context that makes them mean something.
Affiliate disclosure: some links on this page are affiliate links. If you request a quote or buy through them we may earn a commission at no extra cost to you. Nothing on this page changes because of it.
Sierra 3500HD by model year
all years, side by side →Common questions about the 2021 Sierra 3500HD
Source: EPA, NHTSA and manufacturer press kitsDoes the 2021 GMC Sierra 3500HD have any recalls?
NHTSA has posted 5 recall campaigns for the 2021 GMC Sierra 3500HD, 2 of them rated critical. The most serious on file is 24V797000, covering Power Train. There is an active park outside advisory — act on it before driving. Check your own VIN at nhtsa.gov/recalls; a recall applies to specific build ranges, not every car.
How safe is the 2021 GMC Sierra 3500HD?
NHTSA has not published a crash-test rating for the 2021 GMC Sierra 3500HD yet. On the recall record WhichTrim grades it F (57/100), which measures open and severe recalls rather than crash protection.
What are the dimensions of the 2021 GMC Sierra 3500HD?
Transport Canada measured it at 235.4–266.1 in long, 81.9 in wide (body, without mirrors), 79.9–80.7 in tall, on a 141.7–172.0 in wheelbase. Curb weight: 6,338–7,172 lb depending on configuration. Those are its measurements of the North American versions; every figure is in the table above.
What do owners complain about on the 2021 GMC Sierra 3500HD?
Owners have filed 20 complaints with NHTSA about the 2021 GMC Sierra 3500HD, most often about power train, service brakes, electrical system. Complaints are unverified owner reports, so treat the pattern as a signal and the individual report as an anecdote.
Are there service bulletins for the 2021 GMC Sierra 3500HD?
The manufacturer has filed 841 service bulletins and related communications with NHTSA for the 2021 GMC Sierra 3500HD, most often covering engine, electrical system, equipment. The most recent is dated 2026-09-26. A bulletin is not a recall: it is the repair procedure a manufacturer sends its dealers for a condition it knows about, and the work is not automatically paid for. It is still worth knowing — if the symptom matches, quoting the bulletin number at the service desk can save a diagnosis. The document numbers and summaries are listed above.
What we hold, and what an empty row means
Paid vehicle-history reports will not tell you the difference between “nothing happened to this car” and “we never received that record” — both of the big two say as much in their own help pages. Most of what is on this page comes from complete federal registers, so we can tell you which is which, row by row.
| Data | Held | Source | What it covers — or what empty means |
|---|---|---|---|
| Fuel economy & configurations | none | EPA certification records | The EPA does not certify vehicles rated over 8,500 lb GVWR, so heavy-duty nameplates have no entry at all. |
| Emission certificates | none | EPA emission certificates | The EPA published no certificate we could match to a configuration on this page. |
| Recalls | 5 | NHTSA recall campaigns | A complete federal register: every campaign covering this model year, with severity and advisory flags. |
| Owner complaints | 20 | NHTSA complaint database | Also complete, but unverified: these are reports owners filed, not findings. Counts scale with how many were sold. |
| Crash ratings | none | NHTSA NCAP | NHTSA has not tested this model year. Cars are selected for testing, so untested is not unsafe. |
| Service bulletins | 841 | NHTSA manufacturer communications | Everything the manufacturer told its dealers about a defect or malfunction, short of a recall. |
| Investigations | 1 | NHTSA Office of Defects Investigation | Open and closed defect investigations, with the agency's own narrative. |
| Driver-assist crash reports | none | NHTSA Standing General Order 2021-01 | No report has been filed. Only entities named in the order report, and only crashes they hear of — so this is also what an unequipped car, or a manufacturer without telematics, looks like. |
| Specifications filed with NHTSA | 8 fields | NHTSA vPIC, decoded from VIN patterns | What the manufacturer filed under the federal VIN rule — a configuration, not the full trim ladder. |
| Measured dimensions | 7 fields | Transport Canada, Canadian Vehicle Specifications | Length, width, height, wheelbase, track and curb weight, measured on the North American versions. |
| Trims, pricing & equipment | none | Manufacturer press kit | We have not transcribed a press kit for this model year yet. This is our gap, not the manufacturer's — the one row here where an empty cell means we are behind. |
Rebuilt nightly; this page was generated 2026-10-26. Every figure above is traceable to the source named beside it, and the JSON for this page carries the same values with their identifiers.
Sources & method
Safety Signal starts every model-year at 100 and subtracts points per open NHTSA recall campaign by severity: critical 15 (fire risk, park-outside or do-not-drive advisories), high 8 (brakes, steering, airbags, loss of drive power, structure, battery), moderate 6, minor 3 (software, labels, lighting fixed by an update). The most serious recall counts in full and each further one counts 85% of the one before, because a vehicle sold in millions is recalled more often than a rare one without being more dangerous — and because a flat subtraction bottomed the scale out, scoring a vehicle with 22 recalls within a point of one with six. A ≥ 90, B ≥ 80, C ≥ 70, D ≥ 60, otherwise F. Read it as what it counts: recall campaigns on the federal record, weighted by severity. The damping reduces the sales bias by roughly 40% but does not remove it: like our complaint counts, this is not normalized by how many were sold, so a best-seller still scores somewhat worse than an obscure model with the same real risk. NHTSA crash ratings, do-not-drive and park-outside advisories, and the crash, fire, injury and death counts in owner complaints are reported separately on every page and never blended into the letter — a vehicle can hold five stars and a poor letter at once, and where that happens we say so rather than leave you to notice. Because the scale subtracts from a clean sheet, a model year too new to have been recalled, complained about or bulletined scores full marks on an empty record; we label those grades provisional rather than present them as earned.
EPA figures come from fueleconomy.gov vehicle records. Recalls, complaints, investigations and crash ratings come from NHTSA's public flat files, refreshed nightly.