Why Is My Check Engine Light On?
The check engine light is one of the most important dashboard warning lights in any vehicle, but unlike the other warning lights, it’s not exactly straightforward. When the TPMS (tire pressure monitoring system) or the engine temperature warning light comes on, there’s a clear cause.
The check engine light, however, is more of a catch-all warning that can be triggered by a wide variety of issues ranging from minor to severe. When your car’s internal computer detects an issue with the engine, ignition, fuel, or exhaust systems, it will cause the light to turn on—and unless the gas cap isn’t screwed on tight enough, the only way to know what’s causing the problem is diagnostics. With that in mind, here are some of the most common reasons the check engine light comes on and why it’s so important not to ignore it.
Common Reasons the Check Engine Light Comes On
Loose Fuel Cap
If your check engine light turned on right after you fueled up, it’s very possible your gas cap isn’t screwed on tightly. Thankfully, it’s an easy fix—but why does it happen? The gas cap is part of the fuel delivery system; it prevents gas fumes from escaping from the fuel tank and it helps the system maintain the right amount of pressure. Tighten up your gas cap and continue on your way; the light should turn off after about 15-20 miles of driving. If your gas cap is faulty, we can replace it for you.
Faulty Oxygen Sensor
A faulty oxygen sensor is often caused by internal leaks, burning oil, or contaminated fuel with high concentrations of ethanol. Beyond turning on your check engine light, it can lower your fuel economy by as much as 40%. Waiting too long to have your oxygen sensor replaced can lead to damage to the spark plugs or catalytic converter.
Faulty Spark Plugs or Spark Plug Wires
If your spark plugs aren’t firing correctly, or the wires aren’t transferring electricity from the coil to the spark plug, it will cause the check engine light to turn on. When this happens, you’ll likely notice poor performance, engine misfires, lower fuel economy, or a declined throttle response. Like a faulty oxygen sensor, spark plug issues can lead to damage to the catalytic converter. To prevent this, follow your manufacturer’s recommended replacement intervals. These can be found in your owner’s manual, or your service advisor can look them up for you.
Catalytic Converter Failure
The catalytic converter is a part of the exhaust system that’s responsible for converting carbon monoxide in the combustion chamber into carbon monoxide. Beyond the check engine light being on, some other signs you might notice are unusual sounds while driving or discolored smoke coming from the exhaust.
Failing Mass Air Flow Sensor
The mass air flow sensor measures and regulates the air entering the engine to ensure the proper air-to-fuel ratio. If the mass air flow sensor is faulty or failing, it can cause a severe drop in fuel economy, as well as poor performance and engine hesitation.
Faulty Alternator
The alternator keeps your battery charged while you drive; both parts work together to supply power to your vehicle’s entire electrical system, including the headlights, instrument panel, heating and cooling, and radio. If the alternator fails completely, it will prevent the check engine light from coming on—and put you at risk of a dead battery. In addition, your electrical features, including power brakes and power steering, won’t work.
Ignition Coils
The ignition coils generate the electricity needed for the spark plugs to fire properly. If one of them malfunctions, it will cause the check engine light to come on—as well as hesitation when accelerating hard, and engine misfires.
Vacuum Leaks
Every car is equipped with a vacuum system that works to lower harmful emissions—among other functions. If your check engine light is on and you’ve noticed sudden engine surges or abnormally high RPMs, you likely have a vacuum leak. The most common cause of a vacuum leak is damaged or disconnected vacuum hoses or tubes.
Improperly-Installed Aftermarket Alarms
An improperly-installed alarm system can cause a number of issues: draining your battery, preventing your vehicle from starting, and even turning on the check engine light.
Failed Exhaust Gas Recirculation Valve
The exhaust gas recirculation system lowers the amount of nitrogen oxide exiting the engine to help your vehicle run more efficiently and reduce harmful emissions. If it becomes clogged or fails it will trigger the check engine light.
Dead Battery
Batteries generally last between 3 to 6 years; if the battery is faulty or doesn’t have sufficient charge, it won’t send the right amount of power to your car’s computer—which can cause the check engine light to come on. Many newer vehicles have a battery warning light, which makes it easier to tell if your battery is the problem.
Why It’s Important Not to Ignore Your Check Engine Light
Modern vehicles will first try to self-correct any issues the computer detects; if this isn’t successful, it will turn on the check engine light to alert you there’s a problem. While the light is on, your car will continue to try to compensate for the issue; this can lead to poor fuel economy and increased emissions. Some issues can be serious and need to be dealt with right away to prevent expensive damage to the engine or other systems.
In some cars, the check engine light will flash to indicate your vehicle needs immediate attention—but regardless of whether the light is flashing or steadily staying on, it’s important to schedule diagnostics as soon as possible to get the issue resolved.
What to Do if Your Check Engine Light is On
If your check engine light has come on, pay attention to how your car is performing. Does anything seem off? Make a note of when you notice the issue and what your vehicle is doing at the time. Then, schedule an appointment for diagnostics. Letting us know what your car is doing and when will help us diagnose the issue quicker.
For reliable diagnostics and high-quality repairs, you can always trust the skilled team at Johnny’s Auto Service! Contact us today at (626) 966-5212 or request an appointment online.
