Key findings
- A 4.9× larger share than in 2016. 0.77% of complaints mentioned an OBD-II trouble code in January–September 2016, 3.74% in the same months of 2026.
- The biggest jump came in 2026. The share went from 2.42% in 2025 to 3.74% in 2026, while the total number of complaints changed by +5%. In September 2026 alone it was 5.2%.
- Misfire codes are a big part of it. Complaints that mention a misfire code (P0300–P0312) went from 64 in 2021 to 333 in 2026, 15% of all complaints with a code. The models with the most of them are the Ford Escape, Ford Edge and Honda Accord.
- Most big brands follow the trend. For 13 of the 15 brands with the most complaints, a code now appears in a larger share of their complaints than in 2021. The exceptions are Volkswagen and BMW, where the numbers are too small to say much.
Share of complaints that mention a code, by year
Each year counts the same months, January–September, so the latest year compares fairly with earlier ones.
| Year | All complaints | With a code | Share |
|---|---|---|---|
| 2026 | 59,600 | 2,230 | 3.74% |
| 2025 | 56,650 | 1,370 | 2.42% |
| 2024 | 51,510 | 1,128 | 2.19% |
| 2023 | 47,511 | 898 | 1.89% |
| 2022 | 41,014 | 629 | 1.53% |
| 2021 | 38,512 | 562 | 1.46% |
| 2020 | 44,641 | 663 | 1.49% |
| 2019 | 57,239 | 756 | 1.32% |
| 2018 | 47,591 | 502 | 1.05% |
| 2017 | 49,579 | 427 | 0.86% |
| 2016 | 54,846 | 420 | 0.77% |
Month by month
Between 37 and 362 complaints a month mention a code, so single months jump around. The 12-month average smooths that out and shows the long-term trend.
Which codes are behind the rise
The codes owners mentioned most in January–September 2026, with the same months of 2025 and 2021 for comparison. Counts are complaints, and one complaint can mention several codes.
| Code | 2026 | 2025 | 2021 |
|---|---|---|---|
| P0302 Cylinder 2 Misfire Detected, mostly Ford and Honda | 103 | 65 | 16 |
| P1326 Manufacturer-specific code, mostly Hyundai and Kia | 101 | 78 | 23 |
| P0303 Cylinder 3 Misfire Detected, mostly Ford and Honda | 91 | 40 | 12 |
| P0300 Random/Multiple Cylinder Misfire Detected | 89 | 48 | 13 |
| P0301 Cylinder 1 Misfire Detected, mostly Ford and Honda | 84 | 42 | 15 |
| P0304 Cylinder 4 Misfire Detected, mostly Honda and Ford | 83 | 53 | 19 |
| U3000 Control Module, mostly Honda | 72 | 37 | 3 |
| C2200 Manufacturer-specific code, mostly Jeep and Ram | 65 | 26 | 0 |
| P0420 Catalyst System Efficiency Below Threshold Bank 1 | 65 | 38 | 17 |
| P0700 Transmission Control System (MIL Request), mostly Chevrolet and GMC | 50 | 31 | 8 |
Misfire codes fill 5 of the 10 places. A misfire makes the engine shake and, when it's bad, the check engine light flash, so owners notice it and often quote the code their scanner showed.
Codes without a link are defined by the carmaker, not by the OBD-II standard, so their meaning differs between brands.
By system, the number of complaints that mention a code of that type:
| System | 2026 | 2021 |
|---|---|---|
| Powertrain (P codes) | 1,728 | 451 |
| Body (B codes) | 107 | 45 |
| Chassis (C codes) | 274 | 63 |
| Network (U codes) | 276 | 35 |
Powertrain (P) codes are the ones that turn on the check engine light. Body, chassis and network codes usually light other warnings, such as ABS or airbag lights, or none.
By brand
For each of the 15 brands with the most complaints in January–September 2026: the share of that brand's own complaints that mention a code. The last two columns show that share in 2026 and in 2021. Because each brand is compared with itself, the number doesn't simply grow with how many cars the brand sells.
| Brand | Complaints | With code | 2026 | 2021 |
|---|---|---|---|---|
| Chevrolet | 5,085 | 291 | 5.7% | 1.9% |
| GMC | 2,972 | 166 | 5.6% | 1.5%* |
| Kia | 3,323 | 163 | 4.9% | 1.9% |
| Jeep | 3,499 | 156 | 4.5% | 1.7% |
| Honda | 6,121 | 267 | 4.4% | 1.2% |
| Subaru | 959 | 38 | 4.0% | 0.4%* |
| Ford | 10,238 | 392 | 3.8% | 2.0% |
| Ram | 2,485 | 94 | 3.8% | 1.9%* |
| Nissan | 2,234 | 82 | 3.7% | 2.6% |
| Hyundai | 4,298 | 154 | 3.6% | 1.0% |
| Toyota | 4,081 | 93 | 2.3% | 1.5% |
| Dodge | 968 | 19 | 2.0%* | 0.9%* |
| Volkswagen | 1,326 | 18 | 1.4%* | 1.5%* |
| BMW | 1,101 | 6 | 0.5%* | 0.6%* |
| Tesla | 1,526 | 4 | 0.3%* | 0.1%* |
* Based on fewer than 20 complaints with a code: treat it as a rough figure.
A higher share doesn't mean a brand is less reliable. It means that when its owners complain, they more often quote a fault code the car stored. Electric cars like Teslas have no misfire or emissions codes, and their owners rarely quote any code.
Why it may be happening
NHTSA doesn't record why owners mention codes, so these are possible explanations, not findings:
- Reading codes got cheap and easy. A Bluetooth OBD-II adapter and a phone app cost less than a tank of gas, and many auto parts stores read codes for free. More owners know the code before they file a complaint.
- Cars on the road are getting older. Engines with more miles misfire and wear out sensors more often, and those faults set codes.
- Complaints are getting more detailed. Owners who research their problem online learn that the code matters and include it.
- How complaints are filed changes too. NHTSA takes complaints through its website, a phone hotline and other channels, and a change in which one people use can change how detailed the reports are.
Two checks on our own counting: if we count only codes written exactly the way a scanner shows them, like "P0420" with no space or dash, the share still grows from 0.75% in 2016 to 3.52% in 2026. If we count only powertrain codes, the ones behind the check engine light, it grows from 0.54% to 2.90%. So the trend doesn't come from loosely matched text or from other warning lights.
How we counted
- Source: the public NHTSA complaints file with 1,609,883 vehicle complaints in all; complaints about tires, child seats and other equipment are left out. The comparisons use complaints received through September 30, 2026. Each complaint is counted once, in the month NHTSA first received it, even if it lists several components or vehicles.
- A complaint "mentions a code" when its text contains an OBD-II trouble code: a letter P, B, C or U followed by four characters, such as P0420, C1391 or U0100, also when written as "P 0420" or "p-0420".
- Same months every year. Every year is compared over January–September, ending with the last complete month in the file.
- Complaints aren't failure rates. They're unverified reports from US owners. A brand with more cars on the road gets more complaints, and well-known problems attract more reports, so the counts show what owners report, not how often parts fail.
- We don't publish the text of complaints or anything that identifies the people who filed them.
Download the data and cite it
- monthly.csv: every month since 2016 with all complaints, complaints that mention a code, the share, and the strict count.
- makes-by-year.csv: the same per brand and calendar year, for brands with at least 100 complaints that year (2026 runs through September).
You're free to reuse the numbers, tables and charts on this page under CC BY 4.0. Please credit EngineLightCodes with a link to this page, for example:
EngineLightCodes, "Check engine light code complaints: NHTSA data, 2016–2026", data through September 30, 2026, https://enginelightcodes.com/research/check-engine-code-complaints/
We update the page when NHTSA publishes new complaints. Questions or a correction? See how to reach us.