What Does Your Check Engine Light Mean?

12 March 2015
 Categories: , Blog


You're driving down the road without a care in the world when, suddenly, you notice it… the check engine light of your BMW has come on. What does it mean? What's gone wrong? Why, if your car is so smart, can't it tell you exactly what's wrong?

Well, as smart as your car is, it's still not as smart as your mechanic, so of course, the best thing to do is to make a service appointment as soon as possible. But in the meantime, if you want to know the most common reasons your check engine light might be on, take a look at this list:

  • Gas Cap – If your gas cap is loose, open, or even missing, your car will sense that there's a "leak" in the emissions system. And if you're really lucky, you'll find that you just forgot to close and tighten the cap the last time you filled up, so it's worth checking.
  • Mass Air Flow Sensor – This is another fault within the fuel system. This sensor reads the amount of air coming into the engine so that the right amount of fuel is added. If you haven't been replacing your air filter annually, this might be your problem, and if you've noticed your gas mileage suffering, that could be another symptom of this problem.
  • Oxygen Sensor – The oxygen sensor checks the amount of oxygen in the exhaust to make sure the car is using the right ratio of gas to air. Like the mass air flow sensor, this can hurt your mileage.
  • Fuel Injector – These generally last a long time, but if they start to fail, they can trigger the check engine light. In addition to lower mileage, you might also notice the engine misfiring or idling unevenly because of an irregular fuel supply.
  • Spark Plugs – If your spark plugs need changing, you might notice misfiring in your engine, especially while accelerating. Your BMW may not want to respond when you press down the gas pedal, or the car may surge forward unpredictably. If you have been keeping up with your scheduled maintenance, your spark plugs have been regularly replaced, so this is a less likely problem.
  • Head Gasket – Usually, the symptoms of a blown head gasket are quite visible. White smoke coming from your exhaust, your engine overheating, and coolant problems without any visible leak all point to this. However, it can be difficult to diagnose because these symptoms vary depending on just how the gasket has failed.

Considering the amount of overlap between symptoms, often the only way to determine exactly what has caused your check engine light to come on is to open up your car or take it to a qualified mechanic (like those at Autowerkes).