Of the approximately 40 million used cars sold each year, over 450,000 have odometers that were illegally altered, according to federal estimates.

That’s despite decades of efforts to curtail tampering, according to the National Highway Traffic Safety Administration. “Odometer fraud is a serious crime that costs Americans more than $1 billion annually,” an agency spokesman said.

Altering a vehicle’s odometer reading has been illegal since 1972 and was further discouraged by the Truth in Mileage Act of 1986, which requires mileage disclosure when ownership is transferred. In 1994, federal odometer tampering statutes were reworded to underscore that the practice is illegal. But odometer rollbacks are still stubbornly common.

While lower mileage can seal the sale of a used car, drivers of leased vehicles may also be tempted. Those who choose a cheaper low-mileage lease but exceed the limit will incur a penalty at turn-in time, often as much as 20 cents a mile. An extra 5,000 miles a year over a four-year lease could mean a $4,000 bill.

“Criminals target luxury vehicles on ultra-low-mileage lease programs using odometer ‘freeze’ switches or illicit odometer programming tools,” the NHTSA spokesman said.

Online, mileage cheats abound, underscoring the difficulty of rooting out the problem. YouTube videos demonstrate procedures that preventodometers from counting miles and link to sellers offering freeze switches for various vehicles.

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A number of automakers did not respond to requests for comment on odometer tampering. However, General Motors said in a statement that it “uses industry-standard encryption methods to help prevent odometer manipulation, and we continually improve security and redundancies to safeguard vehicle data.”

“Those techniques used are proprietary and confidential,” it added. Pressed further on leased cars and the ways to detect tampering,GM said, “Our team is reluctant to divulge more details on this topic, due to the continually changing landscape.”

The fact that a low-mileage leased vehicle is more valuable at turn-in time than a heavily driven one may help explain why carmakers are seemingly not deeply concerned about odometer rollback.

The practice isn’t limited to leases. Used-car dealers can buy high-mileage cars inexpensively and then repair and clean them. The tires and other parts that show wear are replaced. An odometer rollback and falsification of paperwork complete the job.

Gary Gunn of Royal Oak, Michigan, bought a 2010 Chevrolet Equinox in 2019 from a used-car dealer in Detroit. It was expensive for a nine-year-old car, at $12,650, but looked good and showed only 68,000 miles. Within a week, however, Gunn had to buy a battery, and the transmission started acting up.

He took the car to a Chevrolet dealer, which found that a Missouri dealer had a service record indicating the Equinox had a 174,000-mile odometer reading in July 2016. There was no telling how many miles it had traveled since. Armed with this knowledge, Gunn went back to the used-car dealer, and the vehicle was replaced.

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Automakers could create firewalls to prevent access to a vehicle’s data, but doing so might violate independent service industry agreements. The Motor Vehicle Owner’s Right to Repair Act, enacted by Massachusetts in 2012, ensures that independent mechanics in the state have access to the data and repair paths that dealer technicians use. An informal agreement between automakers and aftermarket-parts associations reportedly made the act national policy. And because odometer calibration is necessary when a dashboard or gauge cluster is replaced, electronic access to the odometer reading has been maintained.

Altering an odometer has never been difficult. Early ones, which were driven by a cable from the transmission, could be turned back by removing the clear cover and using a needle to rotate the number wheel. Simple. Fraud was rampant.

Digital odometers appeared on cars in the 1970s, and by the early 2000s they had replaced mechanical instruments on almost all cars. At first glance, a digital odometer would seem tamper-proof, but just like a computer’s memory, its data can be altered. NHTSA explains on its website that while it’s difficult to detect tampering on old mechanical odometers, it’s even harder on digital odometers, which have no moving parts.

A web search for “vehicle mileage correction” revealed a number of enterprises that offer rollback services. The companies, at least superficially, discourage illegal tampering, but that doesn’t mean they won’t do it. The website of one says, “We require that all customers seeking mileage correction services have a legitimate reason for concern, as it is illegal to alter your car’s mileage and not disclose that information to potential buyers.”

The mileage adjustment costs $120 on one site. The instrument cluster must be removed and shipped to the supplier, which alters the reading and sends it back.

Odometer mileage can also be altered with a tool that plugs into the OBD2 port — a connector that enables mechanics to read service codes reporting failed components.

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To determine how difficult it might be to trim vehicle miles, I bought a $120 odometer rollback tool — the least expensive of those offered on eBay — to give it a try.

The device was for GM vehicles, so I tested it on a 2014 Equinox. The tool is meant solely for altering an odometer’s reading — once powered up, it goes right to a screen that says “Cluster Calibrate.”

The tool correctly read the mileage as 78,624 kilometers, or roughly 48,855 miles, but two attempts to reset the odometer were unsuccessful. Tampering may be relatively easy, but it apparently requires a quality device. After the test, we disabled and discarded the tool, as advised by a law enforcement official.

There are ways to help detect odometer tampering, although they’re not foolproof. For example, a check for excessive wear on the car’s frequently touched parts can provide clues to true mileage. The pedals are good indicators: Be suspicious if those in a car showing moderate mileage, say 45,000, show extreme wear or, because pedals can be changed, no wear. Either might indicate something awry. Also look at the inside of door handles, the steering wheel, armrests and anything else that is touched regularly.

NHTSA suggests that used-car buyers ask to see the title and compare any mileage figure on it with the odometer reading. Maintenance and smog inspection records will also provide a record of mileage at a point in time, as will oil change stickers on the windshield or a door post. If an odometer shows mileage of 20,000 or less, the car should have original tires. You can determine if the tires are newer than the automobile by reading the origin date in the last four digits of the Department of Transportation code on the sidewall. If, for example, those digits are 1517, the tire was made during the 15th week of 2017.

Finally, if you do think the mileage of a vehicle you are considering has been fraudulently altered, NHTSA asks that you contact it or your state’s enforcement agency.