2014 Kia Optima: what breaks, and at what mileage
What breaks on the 2014 Kia Optima
On the 2014 Kia Optima, the failure owners report most often is other engine problem, and the reports cluster around 87,000 miles. The earliest to appear is other steering problem, reported by a median of 5,000 miles. Overall it scores 75 out of 100, high risk for a 2014.
High risk for a 2014 — 75th riskiest of the 270 2014 vehicles we can rate. 787 owner reports; fleet size estimated from this year's own recall paperwork.
What breaks on the 2014 Kia Optima
Owners have reported 64 named failure modes on the 2014 Kia Optima, and the three most-reported carry 36% of everything filed.
Other engine problem leads with 182 reports, about 2.1 per 1,000 vehicles and with the middle half of reports between 50k to 119,000 miles.
Other steering problem follows with 60 reports, usually reported between 110 to 50,000 miles.
Other body or interior problem follows with 41 reports, usually reported between 53k to 100,000 miles. 2 of those reports mention a fire.
By system, the reports fall mostly into engine (281), steering (81) and body (61).
At what mileage it happens
439 of the reports on the 2014 Kia Optima came with an odometer reading, and half of those were filed before 72,000 miles.
Cumulatively, 34% by 50,000 miles, 70% by 100,000 miles and 93% by 150,000 miles of the dated reports had been filed, with 7 filed above the top of the chart.
The busiest stretch is between 0 and 10,000 miles, which alone holds 16% of the dated reports.
25% of the dated reports were filed below 36,000 miles.
In the order they tend to show up: other steering problem around 6k, other visibility problem around 24k, tail light, brake light or signal failure around 40k and other speed control problem around 56k.
Tick median reported mileage Solid middle half of reports Faint 10th to 90th percentile Colour how bad the failure is when it happens
Showing the 12 most-reported failure modes of 64. The full list is in the table below.
How reports accumulate
Every report with an odometer reading, cumulative, from 0 to 200,000 miles. A further 7 reports came in above that, which is why the line stops short of the top. A curve that climbs early is a car with early problems, whatever its total.
- Line share of reports filed by that mileage
- Dashed the median reported mileage
Severity, and what it costs
Across the named modes, 29 mention a crash, 58 a fire, 28 an injury and 3 a fatality. Those are the words owners used in their own complaints, and NHTSA does not verify them, but they are the closest thing in this data to a measure of what a failure actually did.
The average severity weight across every report on this year is 4.79, where a stalled engine or a failed airbag weighs many times more than a rattling trim panel, and a figure this high means the reports are dominated by failures with safety consequences rather than annoyances. The weighting is set out in full on the methodology page.
What the top failures cost to put right, as editorial estimates for an independent US shop rather than figures from NHTSA: other engine problem at $300–$4,000, other steering problem at $350–$2,400, other body or interior problem at $200–$2,000 and other electrical problem at $250–$2,000. Dealer labour, a seized bolt or a part that is no longer made can push any of these past the top of its range.
40% of the reports on this year sit in the engine, transmission, drivetrain or cooling systems — the four where a repair bill is usually four figures.
Every reported failure mode
| Failure mode | System | Reports | With reading | 25th | Median | 75th | Per 1,000 | Typical repair | Severity |
|---|---|---|---|---|---|---|---|---|---|
| Other engine problem | engine | 182 | 122 | 50k | 87k | 119k | 2.1 | $300–$4,000 | High |
| Other steering problem | steering | 60 | 42 | 110 | 6k | 50k | 0.7 | $350–$2,400 | High |
| Other body or interior problem | body | 41 | 15 | 53k | 67k | 100k | 0.5 | $200–$2,000 | Moderate |
| Other electrical problem | electrical | 36 | 17 | 49k | 72k | 88k | 0.4 | $250–$2,000 | Moderate |
| Complete engine failure or seizure | engine | 29 | 15 | 101k | 117k | 128k | 0.3 | $4,500–$12,000 | Critical |
| Other fuel system problem | fuel | 29 | 11 | 31k | 80k | 129k | 0.3 | $300–$2,200 | High |
| Other brake problem | brakes | 25 | 13 | 65k | 80k | 113k | 0.3 | $300–$1,800 | High |
| No-start or intermittent start failure | engine | 21 | 16 | 55k | 68k | 97k | 0.2 | $200–$1,800 | Moderate |
| Other powertrain problem | transmission | 20 | 11 | 51k | 89k | 101k | 0.2 | $400–$4,500 | High |
| Excessive oil consumption | engine | 19 | 9 | 15k | 101k | 112k | 0.2 | $900–$6,500 | High |
| Steering column or shaft failure | steering | 18 | 9 | 50k | 99k | 104k | 0.2 | $600–$2,500 | Critical |
| Other speed control problem | adas | 15 | 9 | 10k | 56k | 89k | 0.2 | $250–$2,000 | Critical |
| Tail light, brake light or signal failure | lighting | 14 | 8 | 6k | 40k | 68k | 0.2 | $100–$900 | Moderate |
| Fuel leak or fuel odor | fuel | 13 | 3 | — | 104k | — | 0.1 | $300–$2,500 | Critical |
| Paint peeling or clear coat failure | body | 13 | 0 | — | — | — | 0.1 | $600–$6,000 | Low |
| Other visibility problem | glass | 11 | 10 | 2k | 24k | 39k | 0.1 | $150–$1,400 | Moderate |
| Cruise control failure | adas | 9 | 9 | 85k | 85k | 97k | 0.1 | $200–$1,400 | High |
| Other lighting problem | lighting | 9 | 6 | — | 59k | — | 0.1 | $120–$1,200 | Moderate |
| Other driver assistance problem | adas | 9 | 7 | — | 72k | — | 0.1 | $250–$1,800 | High |
| ABS module or sensor failure | brakes | 8 | 3 | — | 210k | — | 0.1 | $500–$2,400 | High |
| Other suspension problem | suspension | 8 | 5 | — | 100 | — | 0.1 | $350–$2,000 | Moderate |
| Oil leak | engine | 6 | 3 | — | 140k | — | 0.1 | $250–$2,200 | Moderate |
| Stalling while driving | engine | 6 | 4 | — | 119k | — | 0.1 | $300–$2,500 | Critical |
| Overheating | cooling | 6 | 2 | — | 88k | — | 0.1 | $400–$3,500 | High |
| Loss of braking | brakes | 6 | 2 | — | 294k | — | 0.1 | $400–$3,000 | Critical |
| Airbag warning light or occupant sensor fault | airbag | 6 | 3 | — | 124k | — | 0.1 | $300–$1,600 | High |
| Sunroof failure or glass breakage | body | 6 | 6 | — | 40k | — | 0.1 | $700–$4,500 | High |
| Headlight failure or clouding | lighting | 6 | 5 | — | 79k | — | 0.1 | $150–$1,800 | Moderate |
| Engine knock or bearing noise | engine | 5 | 1 | — | 180k | — | 0.1 | $2,500–$9,000 | High |
| Fuel pump failure | fuel | 5 | 0 | — | — | — | 0.1 | $600–$2,600 | High |
| Fuel injector failure | fuel | 5 | 5 | — | 75k | — | 0.1 | $450–$2,800 | Moderate |
| Seat belt or retractor failure | airbag | 5 | 2 | — | 72k | — | 0.1 | $200–$900 | High |
| Timing chain, belt or tensioner failure | engine | 4 | 2 | — | 111k | — | 0.0 | $1,200–$4,500 | Critical |
| Turbocharger or supercharger failure | engine | 4 | 0 | — | — | — | 0.0 | $1,500–$4,500 | High |
| Backup camera failure | infotainment | 4 | 0 | — | — | — | 0.0 | $250–$1,200 | Moderate |
| Air conditioning failure | hvac | 4 | 4 | — | 55k | — | 0.0 | $400–$2,800 | Moderate |
| Software fault or failed update | software | 4 | 4 | — | 45k | — | 0.0 | $0–$600 | Moderate |
| Other wheel or tire problem | wheels | 4 | 3 | — | 79k | — | 0.0 | $200–$1,500 | High |
| Engine bay fire | engine | 3 | 2 | — | 107k | — | 0.0 | $4,000–$20,000 | Critical |
| CV axle or driveshaft failure | drivetrain | 3 | 3 | — | 30k | — | 0.0 | $450–$2,200 | High |
| Airbag failed to deploy in a crash | airbag | 3 | 2 | — | 67k | — | 0.0 | $1,000–$5,000 | Critical |
| Airbag inflator rupture | airbag | 3 | 3 | — | 62k | — | 0.0 | $0–$0 | Critical |
| Lane keep or steering assist fault | adas | 3 | 0 | — | — | — | 0.0 | $200–$1,600 | High |
| Electrical fire or melted wiring | electrical | 2 | 2 | — | 36k | — | 0.0 | $1,500–$9,000 | Critical |
| Misfire or rough idle | engine | 2 | 1 | — | 55k | — | 0.0 | $250–$1,600 | Moderate |
| Thermostat failure | cooling | 2 | 2 | — | 50k | — | 0.0 | $250–$900 | Moderate |
| Fuel tank, filler or EVAP failure | fuel | 2 | 1 | — | 90k | — | 0.0 | $250–$1,800 | Moderate |
| Alternator or charging system failure | electrical | 2 | 1 | — | 8k | — | 0.0 | $450–$1,600 | High |
| Control module (ECM/PCM/BCM) failure | electrical | 2 | 0 | — | — | — | 0.0 | $700–$3,000 | High |
| Ignition switch, key fob or immobilizer failure | electrical | 2 | 1 | — | 20k | — | 0.0 | $250–$1,500 | High |
| Parking brake failure | brakes | 2 | 0 | — | — | — | 0.0 | $250–$1,300 | Moderate |
| Steering rack, gear or tie rod failure | steering | 2 | 0 | — | — | — | 0.0 | $700–$2,600 | High |
| Wiper or washer failure | glass | 2 | 2 | — | 47k | — | 0.0 | $120–$800 | Moderate |
| Complete transmission failure | transmission | 1 | 0 | — | — | — | 0.0 | $2,800–$8,000 | Critical |
| CVT failure | transmission | 1 | 0 | — | — | — | 0.0 | $3,000–$8,500 | Critical |
| Shifter, linkage or stuck-in-park failure | transmission | 1 | 0 | — | — | — | 0.0 | $250–$1,400 | High |
| Starter failure | electrical | 1 | 1 | — | 49k | — | 0.0 | $350–$1,300 | Moderate |
| Brake line, hose or caliper failure | brakes | 1 | 0 | — | — | — | 0.0 | $250–$1,600 | Critical |
| Blind spot monitor failure | adas | 1 | 0 | — | — | — | 0.0 | $250–$1,300 | Moderate |
| Loss of power steering | steering | 1 | 1 | — | 22k | — | 0.0 | $600–$2,800 | Critical |
| Control arm, ball joint or bushing failure | suspension | 1 | 1 | — | 90k | — | 0.0 | $400–$2,200 | High |
| Alignment fault and uneven tire wear | suspension | 1 | 1 | — | 612 | — | 0.0 | $150–$1,200 | Moderate |
| Tire blowout or tread separation | wheels | 1 | 1 | — | 38k | — | 0.0 | $200–$1,500 | Critical |
| Rust or structural corrosion | body | 1 | 0 | — | — | — | 0.0 | $500–$6,000 | High |
| Unclassified problem | other | 66 | 28 | 44k | 62k | 89k | 0.7 | — | Moderate |
Rate per 1,000 uses a fleet-size estimate derived from recall paperwork for this exact model year. It is a lower bound. Repair costs are typical independent-shop ranges for the failure, not figures from these reports.
How often, against how many were built
Scaled by an estimate of how many of these cars exist, the 2014 Kia Optima draws about 8.9 per 1,000 vehicles, which puts it in the 89th percentile of complaint rates among 2014 vehicles we can rate.
That denominator is the weakest number on the page and it is fair to say so plainly. Rate per 1,000 uses a fleet-size estimate derived from recall paperwork for this exact model year. It is a lower bound.
The working figure is 88,074 vehicles. If the true number is twice that, every rate on this page is half what it says; the ranking against other 2014 vehicles, which is what the risk score uses, is far more robust than the rate itself.
What owners wrote
Verbatim from NHTSA complaint narratives, trimmed for length. The odometer reading is the one the owner gave.
Other engine problem
My kia optima 2014 started a noise near the engine that sounds like a clapping noise. The first kia dealer I took it to said that it is not to worry and is part of the kia engineering design. The second kia dealer I took it to said that the noise is bad news and after further diagnostics, they determined that the entire engine needed to be replaced. Just 5,000 miles into the life of my brand new kia optima 2014. I want people to be aware that if you hear a clapping noise near the top of the engine than please take it into a kia dealer immediately while it is still under warranty. It is not currently a kia recall but I feel it should be since this can lead to replacing the entire engine. Thank you. *tr
I had my car kid optima 2014 2 weeks (800 miles on my new ).the engine was making a knocking noises took it back to dealership it was the piston not working fully they said I was going to have to have engine replaced .I don't want the car ! I'm not happy. *tr
Other steering problem
Tl* the contact owns a 2014 kia optima. The contact was driving 50 MPH when the power steering assist failed. The vehicle was not taken for inspection or diagnosis. The manufacturer was not notified of the issue. The approximate failure mileage was 100.
I complained to the dealer about the rough ride and harsh ride but was told not to worry. I then took it on the highway and the steering pulled to the left and I never felt confident about the steering only to say that it did not feel right and it was worrisome to me. It simply did not feel right to me. I've been driving 50 years and have never felt this uncomfortable driving/steering a car at highway speeds. *tr
Other body or interior problem
On our 2014 optima lx model the passenger seat is adjusted to low to the floor board and my partner which is 61 years old and 4'10" is staring right at the dash cannot see over the top of dash and if air bag should deploy maybe very dangerous not to mention would like to see the outside world . *tr
Tl* the contact owns a 2014 kia optima. While driving, the front driver's seat fell back without warning. The failure recurred multiple times. The vehicle was taken to four different dealers, but the cause of the failure could not be determined. The manufacturer was made aware of the failure, but provided no assistance. The failure was not remedied. The failure mileage was 200. The VIN was not provided.
Recalls on the 2014 model year
NHTSA has issued 7 recall campaigns covering the 2014 Kia Optima, affecting an estimated 381,959 vehicles. A recall is a different kind of evidence from a complaint: it is the regulator and the manufacturer agreeing that something has to be fixed, and the fix is free for as long as the car exists.
The campaigns cover service brakes, hydraulic:antilock/traction control/electron and fuel system, gasoline:delivery:hoses, lines/piping, and fitt. Whether the work was actually done on the car in front of you is a question only the VIN can answer, and the manufacturer or NHTSA will answer it free.
One caution about reading these together: a recall usually raises the complaint count for the same part, because owners who read about it go and file. The mileages stay informative; the counts get noisy.
SERVICE BRAKES, HYDRAULIC:ANTILOCK/TRACTION CONTROL/ELECTRONIC LIMITED SLIP:CONTROL UNIT/MODULE
1,730,192 vehicles 2023-09-25- Defect
- Kia America, Inc. (Kia) is recalling certain 2010-2019 Borrego, 2014-2016 Cadenza, 2010-2013 Forte, Forte Koup, Sportage, 2015-2018 K900, 2011-2015 Optima, 2011-2013 Optima Hybrid, Soul, 2012-2017 Rio, 2011-2014 Sorento, and 2010-2011 Rondo vehicles. The Hydraulic Electronic Control Unit (HECU) may experience an electrical short, which can result in an engine compartment fire while parked or driving.
- Consequence
- An engine compartment fire while parked or driving can increase the risk of injury.
- Remedy
- Owners are advised to park outside and away from structures until the recall repair is complete. Dealers will replace the HECU fuse, free of charge. Interim notification letters, notifying owners of the safety risk, were mailed November 14, 2023. Owner notification letters were mailed March 29, 2024 through June 18, 2024. Owners may contact Kia customer service at 1-800-333-4542. Kia's number for this recall is SC284.
FUEL SYSTEM, GASOLINE:DELIVERY:HOSES, LINES/PIPING, AND FITTINGS
72,848 vehicles 2022-02-17- Defect
- Kia Motors America (Kia) is recalling certain 2013-2014 Optima vehicles that were previously repaired under NHTSA recall number 20V-100. The low pressure fuel hose may be damaged, or missing heat-protective tape, which can result in a fuel leak.
- Consequence
- A fuel leak can increase the risk of a fire.
- Remedy
- Dealers will replace the low pressure fuel hose, free of charge. Owner notification letters were mailed August 2, 2022. Owners may contact Kia customer service at 1-800-33-4542. Kia's number for this recall is SC228.
SERVICE BRAKES, HYDRAULIC:ANTILOCK/TRACTION CONTROL/ELECTRONIC LIMITED SLIP:CONTROL UNIT/MODULE
440,370 vehicles 2021-05-10- Defect
- Kia Motors America (Kia) is recalling certain 2013-2015 Optima and 2014-2015 Sorento vehicles previously recalled under recall 20V-519. Brake fluid may leak inside the Hydraulic Electronic Control Unit (HECU), possibly resulting in an electrical short.
- Consequence
- An electrical short in the HECU increases the risk of a fire while parked or driving.
- Remedy
- Owners are advised to park outside and away from other vehicles and structures until the recall repair is completed. Dealers will install a new multi-fuse, and inspect the HECU for leaks, replacing the HECU if necessary, free of charge. Owner notification letters were mailed on July 2, 2021. This recall supersedes previous NHTSA recall number 20V-519. Owners may contact Kia customer service at 1-800-333-4542. Kia's number for this recall is SC212.
SERVICE BRAKES, HYDRAULIC:ANTILOCK/TRACTION CONTROL/ELECTRONIC LIMITED SLIP:CONTROL UNIT/MODULE
440,370 vehicles 2020-08-27- Defect
- Kia Motors America (Kia) is recalling certain 2013-2015 Optima and 2014-2015 Sorento vehicles. Brake fluid may leak inside the Hydraulic Electronic Control Unit (HECU), possibly resulting in an electrical short.
- Consequence
- If the HECU short circuits, there is an increased risk of an engine compartment fire.
- Remedy
- Kia will notify owners, and dealers will inspect the HECU for leaking brake fluid and replace the HECU if necessary, free of charge. Owners are advised to park outside and away from other vehicles and structures until the recall repair is completed. The recall began October 20, 2020. Owners may contact Kia customer service at 1-800-333-4542. Kia's number for this recall is SC197.
FUEL SYSTEM, GASOLINE:DELIVERY:HOSES, LINES/PIPING, AND FITTINGS
141,774 vehicles 2020-02-21- Defect
- Kia Motors America (Kia) is recalling certain 2013-2014 Optima vehicles equipped with 2.4L Gasoline Direct Injection (GDI) or 2.0L GDI Turbo engines. The low pressure fuel hose may deteriorate and crack over time due to heat generated within the engine compartment.
- Consequence
- If the fuel hose cracks, a fuel leak can occur, increasing the risk of a fire.
- Remedy
- Kia will notify Owners, and Dealers will inspect the low pressure fuel hose for damage or leaking, replacing it as necessary. If no damage or leaking is found, a heat-protective tape will be installed. Repairs will be performed free of charge. The recall began June 12, 2020. Owners may contact Kia customer service at 1-800-333-4542. Kia's number for this recall is SC187.
FUEL SYSTEM, GASOLINE:DELIVERY:HOSES, LINES/PIPING, AND FITTINGS
71,653 vehicles 2018-12-19- Defect
- Kia Motors America (Kia) is recalling certain 2011-2017 Optima, 2012-2017 Sorento and 2011-2018 Sportage vehicles that previously received an engine replacement under recall number 17V-224, warranty, or the Knock Sensor Detection System (KSDS) Product Improvement Campaign. The high pressure fuel pipe that connects to the fuel pump outlet may have been damaged, misaligned or improperly torqued during the engine replacement procedure, possibly causing a fuel leak.
- Consequence
- A fuel leak in the presence of an ignition source can increase the risk of a fire.
- Remedy
- Kia has notified owners, and dealers will inspect and replace the fuel pipe, as necessary, free of charge. The recall began January 17, 2019. Owners may contact Kia customer service at 1-800-333-4542. Kia's number for this recall is SC172.
ENGINE AND ENGINE COOLING:ENGINE
618,160 vehicles 2017-03-31- Defect
- Kia Motor Company (Kia) is recalling certain 2011-2014 Optima, 2012-2014 Sorento and 2011-2013 Sportage vehicles. Machining errors during the engine manufacturing process may cause premature bearing wear within the engine.
- Consequence
- Bearing wear may result in the engine seizing, increasing the risk of a crash.
- Remedy
- Kia will notify owners, and dealers will inspect the engine assembly, and replace the engine if necessary, free of charge. The recall began June 20, 2017. Owners may contact Kia customer service at 1-800-333-4542. Kia's number for this recall is SC147.
Recall work is free at a franchised dealer regardless of the car's age. Check the VIN at nhtsa.gov/recalls before assuming it was done.
How it ranks in the 2014 field
The score at the top of the page, placed among its peers. The zones are the same thresholds the scorer applies, read out of the scorer itself, so the picture and the band word cannot disagree.
Scores are ranked within the model year, never across years, because an older car has had longer to accumulate reports.
- Left fewer and less serious reports
- Right more, or worse
- Marker this vehicle
How 2014 compares with the other years
High risk for a 2014 — 75th riskiest of the 270 2014 vehicles we can rate. The comparison is always within the same model year, so an older car is never penalised for having had longer to break.
Across the 20 model years of this car that carry enough reports to score, 2005 comes out best at 57 and 2019 worst at 80, with 2014 itself at 75.
If the model year is negotiable, 2005, 2003, 2007, 2006, 2004, 2002, 2010, 2009, 2001 and 2008 score lower than 2014 by a margin worth acting on. Same body, same engines, different luck — usually a supplier change or a mid-cycle fix, which the complaint data can show but never explain.
Within the 2011–2016 generation specifically, 2012 is the strongest year at 74 and 2016 the weakest at 77.
Scores compare each year against other cars of the same model year, so a low number on an older car is a real result and not an artefact of age.
Shorter is better. Years with too few reports to score are shown without a bar rather than as a zero, because no data is not good news.
Within the 2011-2016 generation, 2012 Kia Optima scores best at 74 and 2016 Kia Optima worst at 77.
Where to spend the inspection money
The mileages below are where the first quarter of reports for each mode had already been filed, which makes them the point at which a fault is worth looking for rather than the point at which it happens: other steering problem from about 110, other visibility problem from about 2k, tail light, brake light or signal failure from about 6k and other speed control problem from about 10k.
On a 2014 Kia Optima with more miles than that on it, the useful question to put to a seller or a mechanic is whether other steering problem has been dealt with, and if so with what parts and at whose expense. A car that has already had the repair is in a different position from one that has not.
Treat it as where to point the inspection, not as a prediction. A well-maintained example can sail past every mileage on this page, and a neglected one can fail well before the first of them.
What this page cannot tell you
787 owner reports; fleet size estimated from this year's own recall paperwork. Every count on this page is therefore a floor: it is the number of owners who went to the trouble of filing with a federal agency, which is a small and self-selected fraction of the owners who had the fault.
Of those 787 reports, 439 carried an odometer reading, so the mileages here describe 56% of the sample rather than all of it. Owners also round: readings pile up on multiples of ten thousand, which is why this site publishes "about 90,000 miles" and not "91,438".
The failure modes are assigned by software reading the owner's own words, which is accurate in bulk and wrong in individual cases. A mode with a handful of reports may contain a misfiled one.
And nothing here predicts what one car will do. These are other people's complaints, filed years apart, on cars maintained by strangers. Read the page as a map of where this model year has previously gone wrong, then have the specific car in front of you inspected.
Questions this page answers
What are the most common problems with the 2014 Kia Optima?
The most-reported failures are other engine problem (182 reports, median 87,000 miles), other steering problem (60 reports, median 5,000 miles) and other body or interior problem (41 reports, median 65,000 miles). Counts come from owner complaints filed with NHTSA, which are voluntary, so they show what owners bothered to report rather than every fault that occurred.
At what mileage do 2014 Kia Optima problems start?
Other steering problem is the earliest failure mode to show up, with a median reported mileage of 5,000 miles and a quarter of reports before 100 miles. Across all failure modes on this year, the median report sits at 72,000 miles.
Is the 2014 Kia Optima reliable?
It scores 75 out of 100 on our risk index, which is high — 75th riskiest of the 270 2014 vehicles we can rate. The score is a comparison against other 2014 vehicles, not a prediction about any individual car, and it is built from complaint rates, severity and how early failures appear.
Which year of the Kia Optima is best?
Within the 2011–2016 generation, 2012 scores best at 74 out of 100 and 2016 worst at 77. Same body, same engines, different luck.
Where this comes from. Every figure above is computed from NHTSA owner complaints and recall records for this exact make, model and year. Complaints are voluntary and self-selected, so treat counts as a floor. The methodology page writes out each formula, and the same numbers are available as JSON.
What breaks at my mileage Compare with another car
Source Owner complaints and recall records published by the US National Highway Traffic Safety Administration, model years 1996–2027 Figures rebuilt Published by AtWhatMileage How every figure is computed