Your car’s “Check Engine Light”, or CEL, is the little glowing indicator on your dash tells you something needs attention on your car. If you drive an older car, chances are pretty good that you’ve seen your CEL glowing at some point. In fact, a recent CarMD survey suggests that roughly 10 percent of all vehicles on the road have their CELs on right now. And, as cars get more and more complicated, it doesn’t seem to take much to trigger them. But what are the things that cause the CEL to turn on? Based on an analysis of 160,000 repairs by CarMD, here are the top 8 reasons a CEL can turn on.
- Faulty oxygen sensor: O2 sensors measure the amount of oxygen in a car’s exhaust to help the car’s computer inject the appropriate amount of fuel into the engine. A failed sensor can throw off a vehicle’s mpg by as much as 40 percent. O2 sensors commonly fail in vehicles with high mileage.
- Faulty catalytic converter: Generally the catalytic converter fails only after something else goes bad and the engine’s exhaust becomes laded with oil or raw gas. Think bad piston rings or a malfunctioning ignition system that pumps too much gas into the engine..
- Faulty ignition coil: No coil means no spark, and internal combustion engines need spark to run. The coil can go bad by operating under high temperatures or just by getting old.
- Faulty exhaust gas recirculation valve (EGR): The EGR is an emission control system that bleeds exhaust back into the combustion process and helps lower a vehicle’s emissions. A bad EGR valve or blocked system may cause your vehicle to run with a rough idle and engine hesitation, and the CEL may be triggered.
- Loose gas cap: Gas will evaporate around the opening of a loose gas cap. There are sensors in the gas system that look for vapor leaks such as this and will trigger the CEL when they are found. At least this one is simple to fix.
- Bad spark plug(s): If your car isn’t firing on all cylinders, you probably have a bad spark plug or two and this means you’re wasting gas. This symptom often occurs because of bad spark plug wires too.
- Bad mass air flow sensor: This is the sensor that meters the engine’s incoming air and determines how much fuel to inject. If it goes bad, your car’s fuel efficiency can drop up to 25 percent. Fortunately mass air flow sensors are relatively easy to replace and not terribly expensive.
- Leaky vacuum hoses on EVAP system: Loose hoses mean evaporating fuel will not reach its vented destination. This often triggers your check engine light. This is not uncommon on older vehicles because rubber hoses designed to vent gas fumes deteriorate and need replacement.
Source: Reedman Toll Lincoln