Top Five Reasons Why The Check Engine Light Is On
This article is to be a quick guide to the most common problems that cause the car to turn on its 'check engine' light. It is something of an efficient system, meant for a catch-all trouble indicator. The 'check engine' light is wired up to remote sensors all over your vehicle, which is meant to head off trouble before it becomes a big problem.
#1: Failing Catalytic Converter
Additional symptom: Car backfires, emits smoke, smells strongly of exhaust.
This is the most common repair. The catalytic converter is a part of the exhaust system under the car. It's job is to re-burn spent fuel after it leaves your engine, to ensure that your exhaust burns clean and your car gets the best mileage possible per tank of gas. The repair can be kind of pricey because catalytic converters require platinum, a rare precious metal. However, the part is easy to get at underneath the car, so the labor costs to replace it are low.
#2: Spark Plugs or Spark Plug Wires Failing
Additional symptom: Engines sputters and stalls often, runs "rough."
This is the second most common problem with internal combustion engines. Just like the flint on a cigarette lighter, a spark plug ignites the fuel inside your car's engine. These ignitions have to be timed perfectly in cycles of four, six, or eight, depending on the number of cylinders your engine has. Spark plugs and the spark plug wires are sold at any auto parts store and aren't very hard to replace yourself, but a mechanic is still the best bet for a professional job.
#3: Mass Air Flow Sensor Malfunction
Additional symptom: Car stalls often, hard to start.
Along with fuel, your engine needs to have air intake to mix with the fuel. Too little air or poorly filtered air makes it hard for your engine to operate efficiently. The mass air flow sensor is connected to your air intake system, and its an integral part because it signals your engine whether it needs more or less fuel to operate. Replacing this is cheap, but a technical job only a mechanic should tackle.
#4: Dying Battery or Battery Charging System
Additional symptom: Car won't start, or often stalls and can't start again.
This one is pretty intuitive: it's a dead battery. Along with the battery, there's the re-charging system which includes an alternator. Your alternator is powered by the engine, and it acts like a generator reclaiming spent electrical energy to charge the battery again. Either of these parts, or a general failure in the electrical system, will be an immediate problem that has to be dealt with at once.
#5: Failing Vacuum Hose
Additional symptom: Engine runs "rough," unevenly, vibrates heavily, loses power on acceleration.
Vacuum hoses are the central nervous system of your car's engine. They power all the sensors to tell your car's computer the exact state of the engine. An engine has to have a lot of moving parts coordinated in order to function; these hoses monitor part 'A' to tell part 'B' when to turn, so to speak. Think of a vacuum hose failure as a car losing its "coordination." Vacuum hoses are cheap and easy to replace, but very difficult to diagnose, so only a mechanic can tackle this problem.
When in doubt, take the car to a professional service technician, like those at American Transmission Center. A quick diagnostic is usually free, depending on your car's service plan.