What Should I Do When My Check Engine Lights Come On?

You drive along in your car or truck and suddenly a yellow light illuminates on your dash telling you to check or service your engine. If you’re like most car owners, you have little idea what the light is trying to tell you or how you’re supposed to react.

Call it the most misunderstood indicator on your dashboard: Checking the engine light can mean a lot of different things, from a loose gas cap to a seriously misfired engine.

Ignore that warning, and you might end up damaging expensive components. It could also be a sign that your car is getting poor fuel economy and emitting higher levels of pollutants.

What the Light Means

The “check engine” light is part of the vehicle’s on-board diagnostic system – a vehicle computer that monitors performance such as engine speed ( RPM), air-to – fuel ratio, and ignition timing. When problems within the system are internally detected, such as engine failures, deteriorating spark plugs, evaporative problems, or fuel mixtures running rich (less oxygen) or lean (more oxygen), the “check engine” light or “service engine soon” light will be illuminated.

Here are the most common problems that could trigger the engine light check. Keep in mind that the fault code that caused the light to turn on in the first place is stored on your car’s on-board computer, and you can retrieve it using a simple Bluetooth-powered app-linked device to get a precise idea of exactly what’s wrong under the hood. Doing this on your own is going to save you money.

Loose fuel cap

A loose fuel cap is one of the most common reasons why the engine light switches on. The cap is a key part of the car’s fuel delivery system. In particular, it prevents gasoline fumes from leaving the fuel tank and helps to keep the entire system under the correct pressure. If the engine light switches on immediately after the fill-up, pull it over and make sure the cap is not loose — or still on the roof of your car. Sometimes the cap has to be replaced, but it’s not a problem that’s going to hit your wallet hard. Most auto parts stores carry universal-fit gas caps that cost around $15.

Oxygen sensor failure

The oxygen sensor (sometimes called an O2 sensor) measures the amount of unburnt oxygen in the car exhaust system. It sends data to the vehicle’s computer, which uses it to regulate the mixture of air and fuel entering the cylinders. The engine will still run even if the O2 sensor needs to be replaced, but it will burn more fuel than usual. In the long run, a bad O2 sensor can damage components such as a spark plug and a catalytic converter. It may also cause the car to fail the emission test. On average, a quality O2 sensor will set you back around $175, but labor costs will vary greatly depending on the vehicle’s make and model, as well as your geographical location. Finally, keep in mind that most of the late-model cars have more than one O2 sensor.

Spark plug/ignition coil issues

Simply put, the ignition coil generates the electricity needed by the spark plugs to ignite the fuel and air mixture in the cylinders. Classic cars have a single coil, but many modern vehicles use a single coil per cylinder. If your ride has a V8 underneath the hood, you could have eight separate coils. The monstrous Bugatti Chiron has 16 of them. No matter how many you’ve got, a malfunctioning coil will almost certainly trigger the engine light check, but remember, if your car burns diesel, you don’t have ignition coils or spark plugs. Speaking of spark plugs, worn or fouled plugs can cause a variety of problems, including engine failure and hesitancy under severe acceleration. The worn coil may exhibit the same symptoms and may cause the car to shut down unexpectedly. The quality spark plug costs between $10 and $20, while the coil is generally $50. It’s also easier to change your own spark plugs than it sounds.

Catalytic converter failure

The catalytic converter is integrated into the exhaust system of the vehicle. The carbon monoxide generated during the combustion process is converted into carbon dioxide. It’s a fairly simple part, and its failure can often be avoided. That’s good news, because the new one will cost between $200 and $600 depending on the make and model. Every late-model car running on gasoline has a catalytic converter. Performing regular maintenance (such as oil change) on time is the key to keeping your car’s catalytic converter in working order. If you live in the city and mostly drive short distances, take your car on the highway every now and then to make sure that the catalytic converter is not clogged. And, as always, keep your eyes and ears open for unusual sounds or discolored smoke from the exhaust.

Bad spark plug wires

As its name suggests, a spark plug wire transfers electricity from the coil to the spark plug. Without it, the mixture of fuel and air in the cylinders would not be ignited. The vast majority of cars use a single wire per cylinder, but there are models — notably some older Mercedes-Benzes — with two spark plugs per cylinder, and therefore two wires. Symptoms of bad spark plug wires include rough idleness, noticeable drop in engine performance, and lower gas mileage. Expect to spend about $50 on a set of plug wires.

By Jon ‘ShakataGaNai’ Davis, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=3177569

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