What a Mechanic Checks Before You Buy a Used Car

A pre-purchase inspection is an independent mechanic's hands-on examination of one specific used car, done before the sale is final. The Federal Trade Commission says it is "always a good idea" to pay for one, and the defect list on the back of the FTC Buyers Guide is the closest thing to an official map of what such an exam looks at.

Key takeaways

• The FTC recommends an independent mechanical inspection even if the dealer has "certified" the car or sells it with a warranty or service contract, and says a vehicle history report is not a substitute for one.
• The Buyers Guide defect list has 15 headings, from frame and engine to airbags and tires, with specific examples such as tread depth under 2/32 inch and brake pads under 1/32 inch.
• Several checks sit outside that list: open recalls, title brands in NMVTIS, signs of flood damage, the tire date code and whether the engine computer's self-tests have run.
• If a dealer will not allow an independent inspection, the FTC's advice is to consider another dealer.
• An inspection reports a car's condition on one day; it cannot confirm hidden history, and history databases can return false negatives.

What the FTC says about inspections

The FTC's consumer advice on buying from a dealer states that it is always a good idea to pay for an independent mechanic to do a mechanical inspection. The page adds that this applies even when the car has been "certified" and inspected by the dealer or is being sold with a warranty or service contract. The buyer pays the inspection fee; the FTC page gives no dollar amount, so none is quoted here. Fees vary by shop and region, and a quote should be requested before booking.

The FTC also advises asking for a written report with a cost estimate for all necessary repairs, and making sure the report includes the car's make, model and VIN so it is tied to the car being bought. The estimates can then be used to negotiate the price. Separately, it states that a vehicle history report "may list accidents and flood damage, but typically it will not list mechanical problems," which is the gap an inspection fills.

The Buyers Guide window form carries the same message. Who must post that form, and what its warranty boxes mean, is covered in detail in how to read the Buyers Guide sticker before you buy; in short, the federal rule applies to dealers as 16 CFR 455.1 defines them, not to an individual selling a personal car now and then. The front of the current form says, in capital letters, "Ask the dealer if your mechanic can inspect the vehicle on or off the lot." That line has been on the form since the rule was issued in 1984.

The Buyers Guide defect list

The back of the Buyers Guide opens with one sentence: "Here is a list of some major defects that may occur in used vehicles." The list is organized by system. Dealers are required to print it, so it works as a ready-made frame for a conversation with a shop. It is a list of examples, not a federal inspection procedure; none of the FTC pages opened for this article prescribes what a pre-purchase inspection must include, so the scope of a given inspection depends on the shop. Confirm in advance what the shop will examine.

The table below condenses the list printed in Part 455's English Buyers Guide figures (the form as revised in 2016, effective January 27, 2017). Three items carry a measurement printed on the form itself: brake pad or lining thickness, steering linkage play and tread depth. Others refer to DOT or manufacturer specifications that are not printed there.

Airbags and catalytic converters were added to the list by the FTC's November 2016 final rule. Forms printed before that change lack them, but the rule let dealers use up old forms only until January 27, 2018.

Records to pull before the visit

Two lookups take minutes and shape what the mechanic is asked to focus on. Both start from the vehicle identification number (VIN), which the Buyers Guide itself says is needed to use the recall and history resources.

Open safety recalls

The FTC's used-car page points buyers to the National Highway Traffic Safety Administration's free listings of vehicles with open safety recalls, and the Buyers Guide names the agency's safercar.gov address. The VIN search sits on NHTSA's recalls page. In the FTC's words, an open recall means the manufacturer has recalled the vehicle but the repairs are not yet done. A mechanic's inspection does not replace this lookup, because a recall defect may not be visible during a general exam.

Title brands in NMVTIS

The National Motor Vehicle Title Information System (NMVTIS) covers a vehicle's title, most recent odometer reading and brand history, and in some cases theft data, according to the Bureau of Justice Assistance's consumer page. It also includes insurers' salvage determinations and reports of transfers to junk or salvage yards. A "brand" is a status stamped on a title, such as salvage, that tells later buyers about past damage. A branded history is a reason to tell the mechanic where to look hardest, for example at frame, airbag and electrical items on the table above.

Flood signs, tire dates, OBD status

These three checks go beyond the Buyers Guide list, and each has an official source for what to look for.

Flood damage

The FTC's November 2022 consumer alert says to check for signs and smells of flood damage: mud or sand under seats, rust around doors, and mold or strong cleaning-product odors. The Missouri Attorney General's flood-car consumer alert adds a musty or "over-perfumed" smell, water stains, mud or residue in the trunk and under carpet, floor mats and pedals, premature rust or corrosion, and a car that hesitates or runs rough. The FTC notes that a mechanic can check for water damage, which can slowly harm mechanical and electrical systems.

The FTC also points to the National Insurance Crime Bureau's free VIN database, with a stated condition: it can reveal flood damage "only if the car was insured when it was damaged."

Tire age from the DOT date code

Tread depth shows wear, not age. Federal rules require a tire identification number (TIN) molded into the sidewall, and under 49 CFR 574.5 its final four digits are a date code: the first two give the week of the year and the last two give the last two digits of the year of manufacture. The rule requires the full number on only one sidewall of a new tire, so the code may be on the side that faces under the car.

Illustrative example: a code ending in 2423 means week 24 of 2023, which falls in mid-June 2023, so as of October 2026 that tire is about 3.4 years old. A code ending in 0719 means week 7 of 2019, about 7.7 years old by the same count. Both could show tread well above the 2/32-inch line on the Buyers Guide, which is why the date is worth reading separately. This article does not cite a replacement age; the vehicle and tire manufacturers' guidance sets that.

Engine computer self-tests

The on-board diagnostics system known as OBD II, which New York's DMV describes as covering 1996 and newer gasoline vehicles, is read by a shop with a scan tool. Its emissions self-tests are called readiness monitors, each named for the system it checks, such as the catalytic converter or oxygen sensor. A monitor is "not ready" when its test has not been completed, and it finishes only after a specific drive cycle that varies by make and model.

New York's DMV lists four reasons a car can show "not ready": trouble codes cleared with a scan tool after a recent repair, a battery recently disconnected or replaced, a computer that needs a software update, or a pending problem that has not yet turned on the check engine light. For a buyer, a not-ready result means the scan cannot yet confirm those systems, and it is fair to ask the seller why. It does not by itself show that anything was hidden. It can also matter after purchase: New York, citing EPA guidelines, lets only one monitor be not ready on 2001 and newer vehicles for an inspection pass. Other states set their own rules.

What an inspection cannot catch

• Past history. A mechanic examines the car as it is. The FTC says a history report may list accidents and flood damage but typically not mechanical problems, which means each tool covers a different gap and neither covers the other's.
• Database gaps. NMVTIS describes its report as "intentionally concise," covering five key indicators. It says about 87 percent of the US vehicle population is in the system and that, until all required entities report, a search "may yield a false negative." A brand also may apply in one state and not another.
• Insurance-dependent records. The NICB database shows flood damage only for cars insured when damaged.
• Future failures. A report describes condition on the day of the exam. The Buyers Guide list names defects that "may occur"; it does not predict which will.
• Items the shop does not examine. The scope depends on the shop, so a defect in an area outside the agreed scope is not covered by the report.

Frequently asked questions

Does a certified pre-owned car still need an inspection?

The FTC says an independent inspection is a good idea even if the car has been "certified" and inspected by the dealer. Certification is the seller's own process, so an independent mechanic is a second opinion paid for by the buyer.

Who pays for the inspection and what should come back?

The buyer pays the inspection fee, according to the FTC. The FTC suggests asking for a written report with a cost estimate for all necessary repairs and using those estimates to negotiate the price.

What if the dealer will not let the car leave the lot?

The FTC suggests looking for a mobile inspection service that will come to the dealership, or asking the dealer to bring the car to a facility the buyer chooses. If the dealer will not allow an independent inspection at all, the FTC advises considering another dealer.

Is a state safety inspection the same thing?

No. The FTC says a mechanical inspection is different from a safety inspection, which usually focuses only on things that make a car unsafe to drive. A recent safety inspection sticker therefore says little about items such as oil leaks, transmission shifting or the air conditioner, which appear on the Buyers Guide list.

Does a clean NMVTIS report mean the car has no title problems?

No. NMVTIS says about 87 percent of the US vehicle population is in the system and that, until all required entities report, a search may produce a false negative. It also says the system's information is not all that a state may hold in its title records, and advises checking the state's full record before buying.

A checklist for the appointment

1. Get the VIN and run the NHTSA recall lookup and an NMVTIS-based report before booking.
2. Ask the seller in writing whether the car can go to your mechanic, on or off the lot; if a dealer refuses, the FTC's advice is to consider another dealer.
3. Ask the shop for a quote and for what it will examine, using the 15 areas in the table as the list.
4. Ask for the findings in writing with a repair cost estimate and the car's make, model and VIN on the report, to use in negotiating the price.
5. Read the tire date codes on all four tires, checking the inner sidewall if needed, and ask the shop to note flood signs and the OBD readiness status.
6. Treat the result as one day's picture: it does not replace history reports and cannot rule out hidden history.

This article is general educational information, not mechanical, legal or purchasing advice for any particular vehicle. Rules and agency pages change; confirm details with the sources below and your state's motor vehicle agency or attorney general.

Sources

• Buying a Used Car From a Dealer, FTC Consumer Advice
• Used Cars, FTC Consumer Advice
• How to steer clear of a flood-damaged car, FTC, November 15, 2022
• Buyers Guide figures, 16 CFR Part 455 (English), FTC
• 16 CFR 455.1, definitions, Legal Information Institute
• Used Motor Vehicle Trade Regulation Rule, Federal Register, November 18, 2016
• Recalls, NHTSA
• NMVTIS consumer information, Bureau of Justice Assistance
• Tips to Avoid Flood Damaged Cars, Missouri Attorney General
• 49 CFR 574.5, tire identification requirements, Legal Information Institute
• What Do You Mean My Car's Not Ready?, New York DMV