In many cases, the light will simply come back on later. Every car has a vacuum system that performs a wide variety of functions. Most code readers will allow you to turn off or reset the check engine light. If you want to skip a trip to the repair shop, spend a few dollars on a Bluetooth-compatible OBD II scanner (or a more advanced adapter) and download a compatible app like Torque from either the Google Play Store or Apple’s App Store. The engine light doesn’t provide a warning as many people think but only comes on after a system error has already occurred. Replace mass airflow sensor ($340.58) 8. It’s a fairly simple part, and its failure can often be prevented. Some drivers with older vehicles may want to squeeze out as many remaining miles as possible without visiting a service garage. Alternatively, some auto parts stores will run a diagnostic test for free. The check engine light is on and there is a noticeable performance issue: If you are noticing a consistent decrease in performance with the check engine light on, your vehicle may have automatically entered a "limp-mode" to prevent additional damage. Make sure the unit you pick is compatible with your car before buying it. However, he notes, "The engine and the emission control system are so interlinked that the health of the emission control system is a good indication of the general health of the car's engine.". Once, when working on a relative’s car that had lost all power, the ECU codes indicated a problem with the turbo. Finally, keep in mind that most late-model cars have more than one O2 sensor. The check engine light provides an idea — sometimes precise, sometimes vague — of what’s wrong with a car. Also, note that disconnecting the battery will often reset your stereo system. This is often due to fuel not getting burned, which causes a misfire or abnormal detonation. The check engine light is part of the onboard diagnostics system, and displays in a few back-up ways. Try one (or more) of the following approaches to turn the light off. But if I had, I would have wasted time and money because it turned out that the sensor was fine. In such cases, the light should go off by itself after a short time. An inexpensive code reader allows you to find out why the Check Engine light is illuminated. Replace evaporative emissions purge solenoid ($153.70) 9. This is the most common cause of vacuum leaks. This light illuminates in either an amber or red color and is part of the diagnostics system found on your vehicle. Sometimes the cap needs to be replaced, but it’s not a problem that’s going to hit your wallet hard. "My wife's car started running poorly, and there was a check engine light. Check engine lights come in orange, yellow or amber, depending on the manufacturer. If your ride has a V8 under the hood, you could have eight separate coils. 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