![]() Mass air flow sensorįor an efficient burn, the engine’s air-fuel mixture needs to be perfect. When the catalytic converter isn’t operating efficiently anymore, a downstream oxygen sensor detects a change and triggers the check engine light.Īs one of the more expensive repairs related to the check engine light, replacing a faulty catalytic converter might make you fidget. Low-quality fuel and worn engines that burn oil tend to contaminate the interior of a catalytic converter, causing it to overheat and break apart. The converter superheats the compounds and breaks them down into harmless molecules, such as carbon dioxide and water, that exit the tailpipe. Shaped like a muffler, the converter’s interior has a ceramic, honeycomb-like structure covered in reactive elements such as platinum, which triggers a response when exposed to the aforementioned chemicals. Because these harmful chemicals contribute to smog and poor air quality, catalytic converters were implemented in the late 1960s. When gasoline burns in the engine, the chemical reaction creates compounds like nitrous oxides and hydrocarbons that enter the atmosphere. Usually it’s just a matter of tightening the cap, but even if the fuel cap needs to be replaced, the cost averages around $80. This is among the top check engine light causes and the cheapest to fix. When the system tries to pressurize while the fuel cap is loose, missing or broken, the computer sees a massive leak, triggering the check engine light. While it prevents dirt and moisture from entering the fuel system, it performs another role almost no one knows, allowing the fuel system to pressurize.Ĭars perform a self-check for fuel system leaks in the background. This seemingly unimportant part is probably the top reason people ask, “Why is my check engine light on?” Everyone knows what a fuel cap is: The twist-on plastic cap covering the fuel filler neck. An average replacement cost is typically between $300 and $400, including parts and labor. Upstream O2 sensors or precatalytic converter oxygen sensors regulate the air-fuel mixture, while downstream O2 sensors monitor the catalytic converter’s efficiency.Īn oxygen sensor is an inexpensive piece and simple to change. Most cars have two or more oxygen sensors. These codes may be one of the reasons the check engine light comes on. If the value is either higher or lower than the reference, it triggers a DTC, or diagnostic trouble code. An element mounted in the exhaust pipe produces voltage from exhaust oxygen levels, and the voltage is indexed to a value in the onboard diagnostic system. Oxygen sensorĪn oxygen sensor, or O2 sensor, monitors the amount of oxygen in a vehicle’s exhaust. If yours lights up, these 11 systems are the most likely culprits. Major mechanical parts don’t trigger the check engine light in the vast majority of situations. Some engine-related systems are included, like the fuel system and air intake, but for the most part it’s about emissions issues-sensors and valves and the like. Contrary to its name, it doesn’t actively monitor the engine at all. The check engine light is part of a vehicle’s onboard diagnostics system. 11 reasons the check engine light comes on What are the reasons for the check engine light, and what do you need to do to get rid of it? Read on to find out. Is the motor going to fall out of the chassis at 70 miles per hour? In all likelihood, it won’t, but there are reasons for check engine light illumination.Ī warning indicator is among the most common problems you can experience in any vehicle. That malfunction indicator lamp crudely shaped like an engine causes your heart to sink. A little yellow light shines on your dashboard. You’re driving down the interstate and all is well.
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