Can driving with my Check Engine light on reduce my fuel economy by up to 40%? Yes, in many cases. Also, anytime your Check Engine light stays on, your vehicle has increased it's emissions. Have it checked at a qualified repair shop as soon as possible & if it's flashing, stop immediately.

Warning lights for “Service Engine Soon” or “Check Engine.” Ignoring these indicators may result in poor fuel economy performance and require expensive repairs. For example, a warning light may indicate a faulty oxygen sensor is sending more fuel to the engine than necessary, which can result in a 40-percent fuel economy decline. A warning light could also indicate a faulty thermostat, which can prevent a cold engine from reaching its normal operating temperature, resulting in the unnecessary injection of fuel.

Evaporative emission controls. Poorly operating evaporative emission controls can fail to capture gasoline vapors and recycle them to the fuel tank. Faulty controls waste gas and degrade air quality.

 Source: NADA

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