America’s most complained-about engines & transmissions
We mapped the U.S. NHTSA owner-complaint record onto the specific engine and transmission in each vehicle, across 21 engine and 10 transmission platforms with documented defect patterns. The result is a ranking of which powertrains American owners report problems with most.
“A handful of powertrains account for an outsized share of what American owners actually report. The Ford 6F35 alone has logged more NHTSA complaints than any engine in our data, and Ford builds more of these problem platforms than any other automaker. These are owner complaints, not proven defects — but at this volume they stop being noise and start being a map of where the known trouble is.”
Key findings
- The Ford 6F35 is the most-complained-about transmission, with 51,609 NHTSA owner complaints — more than any single engine in this study.
- The Hyundai/Kia Theta II 2.4L is the most-complained-about engine, with 30,029 complaints — and the broader Hyundai/Kia Theta II family totals 48,019 across its variants.
- Ford appears more than any other automaker across these lists (6 of the 22 platforms shown).
- Across the two leaderboards, owners have logged 421,864 complaints against these documented-defect powertrains alone.
Most complained-about transmissions
10 documented-defect transmission families, ranked by total NHTSA owner complaints logged against the vehicles built with each.
| # | Transmission | Complaints | Critical recalls |
|---|---|---|---|
| 1 | Ford 6F35 | 51,609 | 3 |
| 2 | Chrysler 62TE 6-speed Automatic | 19,770 | 0 |
| 3 | ZF 9HP 9-speed Automatic | 18,527 | 0 |
| 4 | Subaru Lineartronic CVT | 16,772 | 10 |
| 5 | Jatco JF016E/JF017E CVT (Nissan) | 16,438 | 0 |
| 6 | Ford DPS6 PowerShift | 15,607 | 0 |
| 7 | GM 6L80/6L90 6-speed Automatic | 12,876 | 2 |
| 8 | Ram 68RFE / Aisin AS69RC | 8,616 | 0 |
| 9 | Honda 5-speed Automatic (B7XA/BAXA family) | 7,168 | 4 |
| 10 | GM 8L90 8-speed Hydra-Matic | 4,090 | 0 |
Most complained-about engines
Top 12 of 21 documented-defect engine families, ranked by total NHTSA owner complaints across every model that uses each.
| # | Engine | Complaints | Critical recalls |
|---|---|---|---|
| 1 | Hyundai/Kia Theta II 2.4L | 30,029 | 1 |
| 2 | GM 3.6L LFX/LLT V6 | 24,486 | 5 |
| 3 | Ford 3.5L EcoBoost (1st gen) | 22,810 | 0 |
| 4 | Ford 5.4L Triton V8 | 20,782 | 7 |
| 5 | Toyota 2GR-FE V6 | 19,075 | 1 |
| 6 | Hyundai/Kia Theta II 2.0L Turbo | 17,990 | 1 |
| 7 | Honda J35 V6 with VCM | 15,171 | 10 |
| 8 | Ford 1.6L EcoBoost | 14,345 | 0 |
| 9 | Honda 1.5L Turbo (L15B7) - Oil Dilution | 11,931 | 0 |
| 10 | Chrysler 2.7L V6 | 10,819 | 0 |
| 11 | VW/Audi 2.0T (EA888) | 10,655 | 9 |
| 12 | Ford 4.6L 2-valve Modular V8 | 9,437 | 2 |
Methodology
ProblemsByVin maps every U.S. NHTSA owner complaint to the specific engine or transmission platform in the affected vehicle, across documented-defect families — each selected for a class action, NHTSA investigation, manufacturer bulletin, or thousands of complaints across the fleet. Counts reflect all NHTSA owner complaints logged against the model years built with each platform, current as of the latest weekly sync. Raw volume partly tracks how many of a vehicle were sold, so these rankings show where documented trouble concentrates rather than a per-car reliability score. NHTSA complaints are unverified consumer reports. Full data and downloads: the data center.
Go deeper
Common questions
What is the most-complained-about engine in the U.S.?
By total NHTSA owner complaints logged against the vehicles built with it, the Hyundai/Kia Theta II 2.4L is the most-complained-about engine in this study, with 30,029 complaints — and the broader Hyundai/Kia Theta II family totals 48,019 across its 2.4L and 2.0T variants. See the full engine leaderboard above.
What is the most-complained-about transmission?
The Ford 6F35 leads the transmission ranking with 51,609 NHTSA owner complaints — more than any single engine in the study. The full top-ten transmission list is above, each linking to its detailed reliability page.
Does "most complained-about" mean least reliable?
Not on its own. Raw complaint volume partly tracks how many of a vehicle were sold and how long it has been on the road. These platforms were selected because each has a documented widespread defect pattern (a class action, NHTSA investigation, manufacturer bulletin, or thousands of complaints) — so the ranking shows where the known, documented trouble concentrates, not a simple reliability score.
Where does the data come from?
Every figure is computed from the U.S. NHTSA owner-complaint and recall record and refreshes with our weekly sync. NHTSA complaints are unverified consumer reports — powerful as aggregate patterns, but individual reports are allegations, not confirmed defects. The underlying data is free to download at /data/.