Failing oxygen sensor
Average repair cost: 261€
Oxygen sensors essentially check to make sure the ratio of fuel to air is correct. When there is too much fuel or too much oxygen going into the engine, the use of this sensor can allow your car’s computer to equalize the issue. Oxygen sensors fail somewhat frequently, this is why it is the most common reason for your check engine light to go on. The reason your sensor might fail is because you’ve neglected taking care of your car or from using gas that is high in ethanol. Besides the obvious reasons that your engine not receiving the correct ratio might be a problem, one of the most serious ramifications of a sensor failure is losing almost half your car’s fuel efficiency (which costs money by itself).
Loose fuel cap
Average repair cost: some cents
If your gas cap is just loose because you’re negligent, then it shouldn’t cost you anything to tighten it. What you do is, get out of your car and tighten it (when the vehicle is stopped). However, if your gas cap is damaged and needs to be replaced, you’re looking at spending a few bucks. A messed up gas cap situation accounts for over seven percent of the situations that a check engine light goes on, which is actually quite a bit higher than a lot of other reasons. You should hope, just hope, that the gas cap is the problem. A lot of other problems will hit your wallet much harder. We recommend you try tightening it first and then see if the light goes off.
Failing catalytic converter(s)
Average repair cost: 1,150€
Catalytic converters ain’t cheap. Having to replace a converter is one of those things you’re hoping is not the case when that check engine light comes on. The converter is part of your exhaust system and turns toxic gases into mostly harmless exhaust. Bad exhaust valves, bad spark plugs, and anything that causes the exhaust gases to be the wrong temperature or consistency can make a converter fail. Not only does it cost a lot to replace converters, there’s probably another underlying problem that caused it to fail, which will cost more money to fix. You should hope, just hope, that this is NOT the problem. However, don’t let the fear of your converter being the problem stop you from getting your car checked out. Your car could start releasing toxic fumes all over the place.
Bad spark plugs/ignition coil
Average repair cost: 360€
The ignition coil charges the spark plugs by converting low voltage electricity from the car’s battery into high voltage electricity that can get the plugs going. Both coils and plugs can fail just from the amount of high temperatures they’re exposed to, as well as due to general aging. If your car stops running or won’t stay running, it might be the plugs/coil, because the plugs aren’t getting enough electricity to ignite the combustion to run the engine. Plugs typically range from $20 to $60 each, your ignition coil would cost $30 to $50 or so, and the labor will probably cost the most. That is if you have a car that uses only one coil. Most cars built from the late 1990s and on use one coil per cylinder. If you have one or several bad coils causing engine inefficiency, you’re looking at a higher repair bill.
Malfunctioning mass air flow sensor
Average repair cost: 420€
The mass air flow sensor figures out the barometric pressure, humidity, of the air going into your engine’s combustion system. The sensor works in collaboration with your oxygen sensor. You car wouldn’t be able to adjust to changes in altitude and outside conditions without it. Needless to say, you need the sensor to keep your car running; and it’s not cheap. Failing to replace a mass air flow sensor can cause your car to lose gas mileage – up to 25 percent. There are a lot of symptoms that your sensor might be failing, including a rough idle, trouble starting, and unexpected change in the position of the throttle. The symptoms may sound familiar, as they’re similar to what happens when the plug wires are failing, which is why you need a professional sometimes.
Faulty exhaust gas recirculation valve
Average repair cost: 300€
Exhaust gas recirculation (EGR) is a system that cuts down the amount of nitrogen oxide that comes out of your car and helps it run more efficiently. It improves efficiency by directing the hot exhaust gases back into the combustion chamber, which warms up the fuel and makes it easier to combust, resulting in higher gas mileage. It also serves the environment well. The failure of this system can cause your car to idle roughly or misfire, because the engine is not circulating the extremely hot air properly. The EGR valve is the most common failure point in this system, which will require you need to replace the valve and clean all the parts, costing just over $300.