What’s wrong with my car? .

There are many reasons your check engine light comes on, some simple to fix, some not so simple

Oxygen sensor malfunction.

The oxygen sensor determines the air/fuel mixture that goes into the cylinders for the pistons to push, detonate, and power the engine. The principal of combustion, in this case internal combustion as it applies to your car’s engine, is predicated on oxygen. No air, no boom. No boom, no go. The oxygen sensor analyzes the oxygen flow and fuel mix, and makes adjustments as necessary to make sure the mix isn’t too rich or too lean in the cylinders. The resulting exhaust gases from the combustion in the cylinders pass through the exhaust manifold, where any residual fuel vapor is burned off. The remaining pollutant gases then pass to the catalytic converter, which converts the toxic gases into something a little more environmentally friendly.

If the oxygen sensor malfunctions, a lot of things are affected. Your gas mileage will suffer drastically. The engine just won’t perform as efficiently or powerfully as possible. If you don’t get the oxygen sensor fixed right away, the catalytic converter will be damaged or destroyed. Catalytic converters are expensive, and they are generally just replaced instead of repaired due to their complexity and use of expensive metals such as platinum, palladium, and rhodium. Think $200 oxygen sensor or $2,000 catalytic converter and other expenses. Yay oxygen sensor!

Catalytic converter failure.

Remember that time the check engine light came on and you ignored it for a few weeks, but then you finally got around to having it checked and it was the oxygen sensor that made the light come on? You made sure the mechanic turned off the check engine light, but you ignored the oxygen sensor and didn’t get it fixed for a month. Now the check engine light is back – and instead of $200 for that oxygen sensor you didn’t want to pay, it needs $2,000 or your car won’t run. The catalytic converter has failed, and it’s taking your car with it.

Hey Sparky, pay attention to the light.

The spark plugs create the sparks that make the air/fuel mixture in the cylinders explode. No sparks, no explosions, no internal combustion in the engine means you are going nowhere, or at best, you’re going slowly, noisily, and inefficiently. You might be one of those lucky people that never has to change the spark plugs (whether they need changing or not is another matter – we’re just talking about having to do the actual work) because you know. With the oxygen sensor, replacing spark plugs is cheap. Repairing the damage you get if you don’t replace them is expensive. You’ll probably have to replace the ignition coil, along with the spark plugs, for around $400. Bonus to all of this: the catalytic converter will probably have to be replaced at this point, too. It’s sensitive to spark bad spark plugs. Are you seeing a pattern here?

Mass airflow sensor is on its way out. Act accordingly.

The mass airflow sensor measures the volume of air flowing into the engine and helps determine how much fuel to inject into the engine. Without this, you get all kinds of funky behavior from the engine. It’s hard to start; it hesitates, drags, or jerks, especially at acceleration; the engine hiccups or idle is too fast or too slow. Without this vital component, your vehicle’s emissions output will go up, and your fuel efficiency will go the other direction.

Check engine? Check gas cap.

If the check engine light comes on right after you pull away from the station, it’s a good bet you need to pull over and check that the gas cap is on tight enough. Check it, tighten it, restart the engine and see if the light comes on again. If it doesn’t, you just fixed the problem!

If the cap is on nice and tight, and the check engine light comes on again, then there is something else wrong. It is possible that the gas cap is loose and won’t tighten anymore, or has a leak due to a worn out seal or a crack. In these cases, it’s a good idea to get a new gas cap and see if that fixes the problem. If the check engine light doesn’t come on after you replace the fuel cap, you’ve just saved yourself time, money, and many sleepless nights.

Of course, if you pull over to investigate and the gas cap is not on at all – as in missing – then you probably should go back to the gas station and look for it. If you can’t find it, a new cap is in your immediate future and will most likely make the check engine light go away.