Taking your potential new used car to a reputable auto repair shop is the best thing you can do. Have it thoroughly inspected by a professional before you buy it. I’ve found paying for an hour of time is generally sufficient to identify everything wrong with the vehicle.
If taking the vehicle to a mechanic is not an option, here are some tips to help keep you from buying a lemon.
Buy a ODB Scanner/Reader
You don’t need to spend a lot, as they’ll all do what you need here. A Bluetooth OBD reader and the TORQ app for you phone seems to be pretty popular/good choice. You can expect to spend anywhere from $35 to $100 on a scanner.
Practice using it on some cars. Some of the stuff may seem daunting, but if you practice it on a car a few times, you’ll get the hang of it, and this will all make sense. You could be saving yourself thousands in repair here, so take a few hours to practice it.
You should be able to do all of the stuff with your scanner in under five minutes total. You don’t have to worry about reading and interpreting data. The main thing you want to do is check for codes in the engine and transmission ECUs.
ECU stands for Electronic Control Unit. Basically, it’s the computer that controls the engine or transmission. They are sometimes referred to as ECM, or Engine Control Module, and TCM, or Transmission Control Module. Sometimes they’ll be referred to as PCM, or Powertrain Control Module.
This is what it’s called when only one computer controls both the engine and automatic transmission. The PCM may be one physical computer, but logically, it’s 2 computers. So if you connect your scanner to a PCM, you’ll still see two separate options, one for the engine, and one for transmission. Do note that if you have a manual transmission, there won’t be a transmission computer.
So when you connect to each one, there should be no codes in either. If there are codes, there’s an issue. It may be minor, it may be major. Google it if you want, but not knowing what the codes mean, your best bet is to walk away. If your scanner is a better one, you can also check other modules (computers) for codes. However, it’s pretty common on newer cars, especially European, to find obscure codes in obscure modules. Normally they’re not an issue.
Focus on the Engine and Transmission. ABS (antilock brakes) and SRS (safety restrain system…airbags, seat belts, etc) modules normally shouldn’t have codes lingering either. Make sure to also check after test driving. The codes may have been reset by the seller to hide a problem (more on that in the next paragraph). They may have returned during your test drive, so check again!
Use the scanner to check the monitors on the engine ECU/Computer. Monitors are a series of self-checks the ECU does on the engine. All applicable monitors should be set (passed/complete). They get reset when you clear the check engine light, or when you disconnect the battery (usually).
If all of the monitors haven’t passed, then it’s likely the person selling it has reset the check engine light recently (may be trying to hide a problem), or there’s a problem that isn’t allowing the monitor to complete. Not a good sign. Walk away. To complete all of the monitors can take quite a few miles and sometimes several days.
Crank the Engine Without Starting It
What you want to do is listen to the engine during a continuous crank. On American cars and on Mazdas, this is easy, as they have what’s known as a Clear Flood Mode. You turn the key to the on position, wait a few seconds, depress the gas pedal all the way, then try to start it.
The engine will crank away without starting for as long as you hold the key (or in the case of a push-button start, until you hit the button again). If the engine starts, quickly let off the gas so you don’t rev up the engine too high and try it again. You’ll want to listen to it for a good 10 seconds or so. This is a very easy way to check compression on an engine.
The main thing you hear when cranking an engine is the electric starter working to try and spin the engine. As a piston comes up and compresses the air, the starter has to work harder to spin the engine, and the speed/pitch of the starter changes. Once the piston comes back down, it’s easier to spin the engine, so the speed/pitch changes back, and then repeats as each consecutive piston moves up in the compression stroke.
Every engine sounds different, but they all should have a very steady rhythmic starting noise.
For reference, here’s what a normal cranking sound should be: https://www.youtube.com/watch?v=6v0h_Ygqox0
Here’s what a low compression cylinder cranking sounds like. It’s at about :55 secs: https://www.youtube.com/watch?v=pOghpmVhVng
If you listen closely, you’ll hear the unsteady rhythm. Loss of compression is usually piston rings, valves, or head gasket. All costly. If the engine sounds funny when cranking, walk away.
If the car you’re looking at doesn’t have a clear flood mode, you can remove the fuel pump relay in the engine compartment fuse box, which turns off the fuel pump. Most cars have one, but some don’t. Some cars can be a real PITA to disable it from starting.
Google the car you’re looking at with something like “YYYY Make Model clear flood” or “YYYY Make Model disable fuel pump” and see if there’s an easy way to achieve this.
Practice this beforehand on cars you have access to if possible to tune your ear to the sound. You can also do this periodically on your own car to see if any problems are arising.
Check the fluids
All of the fluids will have minimum/maximum marks. If fluids are low, someone has not been maintaining the car well, or it has developed a leak. Not a good sign.
When checking the engine oil, it should range from clear to black. If it looks like a chocolate milkshake, there is a major problem. RUN AWAY. You can also smell the oil on the dipstick to see if it smells like gasoline. If it smells like raw gasoline, the engine is either injecting way too much fuel or you have bad piston rings. Either way, they’re bad.
If the oil level is WAY above the full mark, by an inch or more, then either some other fluid is making its way into the engine, which is very bad, or someone sucks at doing an oil change.
Remember to check the oil with the engine off and on level ground.
Check the coolant in the reservoir. It should be green, pink, red, yellow, orange, blue, or purple, depending on the manufacturer. If it’s rusty, walk away.
Remove the radiator cap (only if the engine is cold) and look at the cap and in the radiator. If you see any rust or chunky/gritty brown stuff, walk away. If it’s just water, walk away. Note: Ford’s yellow coolant almost looks clear.
Check the automatic transmission fluid. For the most part, it should be red, but sometimes amber or green. It may be black. That’s dirty. Not a deal-breaker, but they haven’t been keeping up on maintenance. It should not smell burnt, though. That’s bad. If it looks like strawberry milkshake, that’s really bad.
Check the level on automatic transmissions while the engine is running in Park and after driving it and getting the transmission good and hot. The only exception is most Hondas. That’s checked after driving but with the engine off. Google it for the car you plan on looking at to make sure. Many new cars don’t have transmission dipsticks, so again, you’re SOL there.
Start the engine and listen for noises
The engine should be cold. If it’s at operating temperature, the seller may have warmed it up to hide some cold start engine noises. Be wary. If it makes any unusual noises, walk away.
Check the maintenance records
If the vehicle has consistent oil change records at an oil change place, at least they’ve been changing the oil. Unfortunately, oil change places only check easy profitable stuff. It’s better than nothing, though.
If the records are all at an independent shop, that’s better. Indy’s will usually do a pretty thorough check up on the car when servicing it.
If the vehicle has all dealer records, that’s the holy grail. Dealers will find any nick nack that’s wrong and upsell it. They also commonly don’t do thorough diagnostics. This is an unfortunate effect of the way dealer shops operate.
So if it needed repairs, on top of having new parts that needed replacing, it may have other new parts that it didn’t even need. Plus those new parts will be good quality OEM parts, not chines junk of questionable quality.
Check that everything works on the car
Check the A/C, the heater, the windows, the locks, the mirrors, the head/parking/brake lights, etc. If the owner neglected to fix obvious problems, what else did they decide not to fix?
Look under the hood, look for any hokey work
Random zip ties holding things on, tape, broken plastic pieces, a battery that can move around if you push on it, wires hanging, etc. If it looks like unprofessional work has been done on what you can see, how bad is what you can’t see?
How does the car look?
Is it dirty, full of scratches, stained? If the owner cares so little about the interior/exterior, they probably have the same attitude toward the mechanical part of it.
Check the tires
Aside from general condition, do they all match? If all the tires are different, they’re cheap/broke, and have probably cheaped out on a lot more than just tires. Lay your hand flat on the tire tread and light feel around the tires. If you feel a repeating pattern of flat spots/dips, you have suspension problems.
Look Under the Car
Look for oil stains. Look and smell for gasoline or coolant stains. Look to see if the various shields and covers are there. Check the condition of the exhaust system. And check to see if the catalytic Converter is there!
Try to stay away from used car dealers
Used car dealers get the majority of their cars from auctions. A lot of cars that go to auction are sent there by someone that doesn’t want it, usually because there are problems. Not all, but many.
New car dealers send trade-ins that are too old or the wrong make to put on their lot, and some of those are decent. However, the small used car dealers usually buy the bottom of the barrel cars at auction. They’ll fix the minimum needed with the cheapest parts possible to maximize profit. They’ll make it look pretty, though. Good chance you’re buying a polished turd.
Not all used car dealers are bad, though. Check reviews. Look at what they have on the lot. If they have a lot of high resale value cars on the lot, they’re buying the good stuff at auction. If all of their cars are under $10k, with a lot under $5k, move on.
Test drive the car
Drive it at different speeds up to highway speeds. Brake easy, brake hard. Find a crappy road or railroad tracks to drive over. Make sure there are no noises or vibrations.
Get it good and warm. When you’re done, open the hood and take a good whiff. Make sure there are no strong smells like burning fluids or other things.
Look under the car and see if anything is dripping or the bottom of the engine is covered in fluids. Bring a flashlight, it can get dark under there. Don’t be alarmed if you see water dripping under the car at about the same area as the base of the windshield/firewall. If the A/C or defroster was on, that just condensates from the A/C system. Touch it. If it’s not oily and looks/feels like water, it should be OK.
If you’re test-driving a manual car, the clutch engagement point should be somewhere in the middle of the clutch pedal travel. If it’s right at the top or right at the bottom, clutch repairs are in the near future.
Don’t trust the person selling the car
Trust your eyes, your ears, and your instinct. You don’t know this person, they may be lying about the car, or try and tell you that the thing you’re worried about is no big deal, it’s just this or that.
Or they had a guy check it out and it’s a really easy/quick fix. Be patient and find the right car.
If something is fishy or doesn’t seem right, move on to the next car. A car is a pretty big expense.
Most people budget for the purchase price of a car and don’t consider there may be a considerable extra expense in fixing major problems. Minimize the possibility of those extra expenses by inspecting the car the best you can.
I would recommend running through these things, and any others you want to add, in your current car, your parents’ cars, friends’ cars, etc. Do it several times. Get comfortable in making these checks so that when you’re doing them in front of some stranger in their car, you won’t forget anything.
Check for Accident Repairs
When you look under the hood, the color of the metal in the engine compartment area should be the same color as the car.
If you see different colors or primer, it’s had body repair. Also, if you look at the reflection in the car’s exterior paint up close and at an angle, you’ll notice that the reflection has a wavy pattern to it. That’s called orange peel.
Every car has it from the factory, except for super high-end cars. The orange peel pattern should be consistent all the way around the car. If the pattern changes in certain parts of the car, it’s been repainted in that area. Good chance it had an accident.
Another thing you can do is take a small magnet with you. You’re going to place the magnet against the car in as many areas as you can. Make sure you wrap it in a microfiber towel or something soft so you don’t scratch the car (it’s not your car).
The magnet should attract itself to the body and even stick to it. If there are spots where the magnet doesn’t stick as strong or at all, there is body filler there. It’s had bodywork.
Do keep in mind that some body panels aren’t magnetic on some cars. If you can’t get the magnet to stick anywhere on an entire panel (like the fender or hood) then you probably have a non-magnetic body panel (maybe fiberglass or aluminum). It’s possible that the whole body panel is covered in Bondo, but that would be rare, as that would be an extremely poor repair.
Buying used from a dealership: Ask to see the title
This is a “protect yourself” tip: If you are buying a used car from a dealer or private seller, ask to see the title. If they won’t do that, ask to see a copy of the title with the previous owner info blacked out. It should be a red flag if they refuse or blackened out more than just the registered owner’s information.
Why? First to make sure they have the title. When I was young and dumb, I was once burned by a licensed motorcycle dealer not having the title and lying about it. Although rare, some sellers don’t have their ducks in a row when selling a car and will sell the car before all of their documentation is completed.
This can turn out really bad for you if the seller never gets you the title or registers it to you. In my case, the dealer failed to tell me it was a consignment sale, failed to give the owner the money from the sale, which meant the owner never gave the title to the dealer. The dealer then suddenly closed his business. It leads to a large lawsuit with many involved parties.
Secondly, seeing the title will potentially allow you to see how many other dealers the car passed through before yours. In most states, dealers are supposed to record a running list of dealer transfers. Seeing a dealer-to-dealer transfer isn’t an automatic red flag. Dealers swap cars ALL THE TIME when a customer wants a certain car. Dealers also get inventory from auction ALL THE TIME (more on this later).
What is a red flag is an incomplete log, such as not seeing your dealer logged on the title’s running list or several dealer-to-dealer transfers. Several transfers are a sign that it is a lemon that keeps getting passed around.
Third, check the title to make sure the title isn’t “branded”, such as being a salvage car, flood car, scrap car, etc. You’ll also see if there is an outstanding lien. Runaway and don’t look back if it’s a branded title unless the seller is honest about it and you know what you’re getting into.
Buying a branded titled car is NOT a risk that an average person should venture into. Best case scenario? The car was totaled from simple cosmetic damage such as hail damage. Average case scenario? The car was in a crash in which the damage exceeded what the car was worth.
Worst case scenario? The crashed car was fixed just barely enough to look good but still has a bent frame, has missing airbags, has unknown amounts of hidden mechanical damage, has severe electrical issues, etc.
Bonus Info: Like a dirty secret of the industry, it isn’t just low cost and questionable cars that get sent to auctions in modern times.
Lease returns? The dealers have zero ownership of lease returns. It’s the leasing company that does. Most lease returns are sent to auction.
Low mileage trade-in’s? Many get sent to auction by dealers that can’t easily sell the vehicle. An example being a Jeep dealer that is flooded with passenger car trade-ins and wouldn’t be able to sell yet another one.
A dealer can’t sell a normally good vehicle after a couple of months for whatever dumb reason? It’s sent to auction.
Brand new cars when a dealership goes out of business or when they just consolidate? They’re sent to auction.
People would be shocked that almost all dealerships heavily supplement their used car inventory from auctions, or buy from wholesalers that get them at auctions. Just assume the used car you’re looking at came from an auction unless the dealer came to prove otherwise.
Hint: Dealers hate saying it was an auction vehicle because of the stigma and will instead simply say it was a trade-in. Don’t believe it unless they prove it. They don’t consider it a lie because it was likely a trade-in at another dealer, but your dealer likely got it at auction.
NEVER, EVER BUY FROM A “BUY HERE, PAY HERE” DEALER. It’s a 99.9% chance they are a scum dealership catering to people with no credit or people that are completely clueless to interest rates and such. For those with no credit, you’re better off saving what you can and then posting a wanted ad on Craigslist for a cheap car.