Common Repairs in Used Cars

October 1st, 2015 by

In addition to the sticker price, you should be expecting to dish out some additional money when you buy a used car. Chief among those additional charges will be repair bills, as it’s likely your “new” car will inevitably need some work. Even if you purchased a vehicle that was in great condition, there’s no way around the aging (and subsequent failing) of some parts.

A 2014 CarMD Vehicle Health Index report analyzed the most common repairs among used cars. We’ve listed some of those below, omitting the replacement fuel cap (#3), replacement mass air flow sensor (#6), replacement thermostat (#8) and replacement Exhaust Gas Recirculation valve (#9). It’s a good idea to briefly read up on these individual parts so you can better identify when they’re starting to fail.

In the meantime, you should read our guide to some of the more popular and well-known parts below. This way, prior to heading into your local used car dealers in Lexington, Kentucky, you can better anticipate the extra money you’ll be throwing into the used car…

Oxygen Sensor


This part, which, as Keith Griffin of explains, can “negatively impact fuel economy by as much as 40 percent,” is the most common repair among used cars. Featured in the exhaust manifold, the tool monitors how much unburned oxygen is still in the exhaust as the exhaust exits the engine. The oxygen levels help determine whether the fuel mixture is burning “rich” (significantly less oxygen) or “lean” (significantly more oxygen).

Why is this important? Gasoline-powered engines use a ratio of air and fuel to burn as efficiently as possible. Following combustion, the oxygen sensor essentially determines whether the fuel is being wasted. If this isn’t working, you could unknowingly be decreasing your vehicle’s fuel efficiency, thus losing yourself money.

You can identify whether your car’s oxygen sensor has failed by how the car is operating. If you notice your car is struggling while idling or jerking when reaching high speeds, this could be an indication. Regardless, your car should notify you via the check engine light.

A typical oxygen sensor repair comes in around $250. Like the other parts mentioned on this list, there’s no avoiding a replacement, as the sensor is essential to your car.

Catalytic Converter


You’ve likely heard this part mentioned by mechanics and car enthusiasts, but we wouldn’t blame you if you have no idea what the catalytic converter actually does. To put it simply, the “vehicle emissions control device” essentially takes the pollutants in your gas and converts them to less toxic pollutants. To get the desired result, the catalytic converter with catalyze a redox reaction, meaning the exhaust won’t be as damaging to the environment. In particular, the converter removes carbon monoxide, nitrogen oxide, and hydrocarbons from the gas, helping prevent the development of poisonous gasses, smog and acid rain.

Unfortunately, it’s not very easy to identify when this particular part isn’t working. Mechanics are often required to remove the entire part to determine whether it’s malfunctioning. Trouble accelerating could be a sign that the part is failing, as would a drop in fuel efficiency. If the problem gets too bad, the increased exhaust will prevent your engine from even running.

A broken catalytic converter could be attributed to the use of lead gasoline, as well as over-use of fuel additives. A failing exhaust valve or “fouled plugs” (which cause all unburned fuel to overheat the part) could also be attributed to a catalytic converter’s demise.

If replacement of the part is covered by warranty, you’ll want to get down to a mechanic as soon as possible. The positive? It’s a relatively common repair, and CarMD listed it as the second-most common fix among used cars. The negative? It’s going to set you back financially, as the part is estimated to cost around $1,150.

Ignition Coils/Spark Plugs


The fourth-most common repair for used cars, both of these parts are essential in igniting the fuel. The coil, sitting in the ignition system, takes the battery’s low voltage and transform it into thousands of volts of electricity. This is then sent to the spark plug, where an electric spark helps ignite the fuel. When you hear a car commended for it’s excellent “electrical performance,” there’s a good chance that the spark plugs (and, vicariously, the ignition coils) are doing their job.

If your ignition coils are failing, there will be an assortment of warning signs. If you notice that your car is backfiring, this likely means that unused, non-ignited fuel is being pushed through the exhaust system. You may find that your vehicle is having issues starting, the vehicle is stalling, or the engine is misfiring. Similar to the other issues on this list, you may find that your fuel economy is also diminishing.

The symptoms of a dying spark plug are pretty similar. If you notice your engine is either vibrating or letting out an odd noise while you’re idling, that could certainly be a sign. A lack of a spark could also prevent your engine from even starting, and it could also make your car stall. You may also notice an issue with acceleration, as well as a surging engine (when the vehicle jerks around or starts and stops frequently). Of course, a bad spark plug will also lead to you wasting plenty of money on unused gas.

If you find yourself needing to replace the two parts, expect to drop at least $400. Without the ignition coils or spark plugs, it’s doubtful that you’ll even make it out of your driveway.

Fuel Injector


This part isn’t as popular as those mentioned above, but it’s just as (if not more) important. The fuel injector serves as the main delivery system for fuel used in the engine, replacing the function of carburetors. While the previous part would rely on a suction from the intake air to draw fuel into the airstream, a fuel injector instead distributes a fuel-air mixture into the cylinder, allowing for a more precise measurement of fuel. This can help improve power and fuel efficiency.

A bad fuel injector has some unique indications that it’s not working properly. If the part is malfunctioning, your engine will be receiving an irregular amount of fuel. This will mean the engine’s power will fluctuate, as opposed to a smooth and gradual ride. You may also notice the engine misfiring or an awkward idle, as well as decreased fuel efficiency. If the part has a small crack, you may see some leaking fuel, as well.

Repairing a fuel injector isn’t as common as the fixes listed above, but it’s still something to look out for, as the CarMD report ranked it tenth among used car fixes. If you have to replace the part, it’s going to cost you around $550.


We don’t want you to panic and anticipate having a $1000-plus bill. There are plenty of instances where a buyer had absolutely no issues with their used vehicle. However, it’s always a good idea to be prepared, and you should now have a better understanding of what to expect and what to look out for.

If you are in the market for a used car, head down to Dan Cummins used dealership. Their lot of used vehicles are all operating in tip-top shape, and you’ll be thrilled with their variety.