What To Do About an Illuminated CEL

The small glowing indicator on your dash tells you something needs attention on your car is your Check Engine Light, or simply “CEL.” If you drive an old car, chances are good that you’ve seen your CEL illuminate at some point. And, as vehicles get more and more complicated, it doesn’t seem to take much to trigger these lights.  But what are some things that cause the CEL to turn on? Based on a CarMD analysis of 160,000 repairs, here are the top 8 reasons a CEL can turn on:

  • Faulty catalytic converter: The catalytic converter fails generally only after something else goes bad and the engine’s exhaust becomes laded with raw gas or oil. Think of bad piston rings or a malfunctioning ignition system that pumps excess much gas into the engine.
  • Faulty oxygen sensor: O2 sensors measure the amount of oxygen in a vehicle’s exhaust to help the vehicle’s computer inject the right amount of fuel into the engine.  According to this Chrysler, Dodge, Jeep and RAM dealer in Wrightsville, PA, a failed sensor can throw off a vehicle’s mpg by as much as 40%. O2 sensors usually fail in vehicles with high mileage.
  • Faulty ignition coil: Internal combustion engines require spark to run, and they can’t with ignition coils that don’t work. The coil can get ruined by operating under high temperatures or simply by getting old.
  • Faulty exhaust gas recirculation valve (EGR): This is an emission control unit that sends exhaust back into the combustion process lower’s a car’s emissions. A bad EGR valve or blocked system can cause your vehicle to run with a rough idle and engine hesitation, and the CEL can be triggered.
  • Bad spark plug(s) and/or wire(s): If your vehicle isn’t firing on every one of its cylinders, you probably have a bad spark plug or two and this means you are wasting gas. This may occur because of bad spark plug wires, too.
  • Bad mass air flow sensor: An air flow sensor is the sensor that meters the engine’s incoming air and determines how much fuel to inject. If the mass air flow sensor goes bad, your car’s fuel efficiency can drop up to 25%. Fortunately, mass air flow sensors are easy to replace and not terribly expensive.
  • Leaky vacuum hoses on your EVAP system: Loose hoses mean evaporating fuel won’t reach its vented destination. This typically triggers your check engine light. This isn’t uncommon on old vehicles because rubber hoses designed to vent gas fumes run down and need replacement.
  • Loose gas cap: Gas will evaporate around a loose gas cap’s opening. There are sensors in the gas system that seek out vapor leaks such as this and will trigger the CEL when they are found. At least this one is easy to fix.

Did you know that a recent CarMD survey suggested that roughly 10% of all vehicles on the road have their CELs on right now? That sounds scary, but if drivers work to solve any CEL issues when they occur, then that percentage can go down!

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