Check Why Your Check Engine Light Comes on Before Selling

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There are five major reasons your check engine light comes on. One of the 5 is really cheap to fix but the other four, not so much. It’s important to make sure your used car has none of these problems before going to sell it. Otherwise, no savvy buyer will consider your car.

Plus there’s the fact that ignoring your check engine light can be extremely costly. Most repairs when caught early can cost you less than $400.

Ignorance is not bliss – a major repair bill can be north of $1,500, according to research by (CarMD makes a on-board diagnostic reader, commonly referred to as an OBD device.)

They have also researched the most common repairs in used cars, which could be helpful when it comes time to sell your used car.  Buyers may ask if you have made those repairs so be informed about them ahead of time. Nothing worse than being caught off-guard.

Matthew Wright,’s car repair expert, has written extensively about check engine lights. As he points out, the check engine light could come on for any reason for any problem under the hood. Clicking on the link above could help you find check engine light problems by brand such as Jeep and even Isuzu. Matthew is nothing if not thorough.

So, what’s the cheapest reason your check engine light comes on? It’s as simple as not screwing your fuel cap on correctly. (You won’t have a problem with certain Fords because they eliminated fuel caps.) Unscrew it and put it back on.

See if your check engine light resets itself.

Now for the bad news: the light could include a really expensive repair. Your catalytic converter when it fails is going to cost you probably more than $1,000. As outlined below, your catalytic converter is going to fail especially if you ignore your check engine lights.

Why’s that? The most common reason is a failed oxygen sensor. Fixing it is a lot cheaper than a new catalytic converter (about one-fourth the cost). Where it becomes really expensive, though, is if you ignore it because it can reduce your fuel efficiency by 40 percent. Sure, gas is cheap right now but do you want to add 40 percent to your fuel bill?

Another way to get poor fuel economy is if your mass airflow sensor needs replaced. That’s going to cost you about $425. Ignoring it is going to reduce your fuel economy by about 25 percent and, as we said with the oxygen sensor, why add 25 percent to your fuel bill?

Another common reason your check engine light comes on is the failure of your spark plugs or wires, which is going to set you back almost $400 (depending, of course, where you live). When these fail, without repair, your ignition coil can fail for additional expense. Ignoring both leads to the dreaded catalytic converter failure and an expense repair of $1,500.

So, how can you detect exactly what your check engine light means? The best way is getting a device that reads your onboard diagnostics. Get one that has a corresponding website that can explain the error readings in simple terms. Using the OBD readers can help you avoid having problems when you bring your car in for repair. They are great tools if your car is prone to check engine lights. Matthew Wright explains if you’re going to need an OBD tool or a Scan Tool. (Hint, it all depends on how many vehicles you oversee.)

By the way, the simple repair you shouldn’t do? Put a piece of electrical tape over the light. That could lead to some really expensive repairs down the road.

By the way, CarMD provides some other helpful information. It has published a list of the 100 best used cars. It looked back 10 years from 2011 prior. That’s a prime market right now for used cars. It might be worth your while to explore the list.

Other important research that CarMD has done is on the most reliable used car brand. It might surprise you, as it did when I first wrote the story, that Hyundai is tops when it comes to reliability. The honor used to belong to Toyota.

So, regardless of how reliable your car is, before you go to sell it make sure the check engine light isn’t on. It’s going to make your sale that much easier.

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