In most situations, the cause of a gas cap light is an improperly threaded or loose gas cap. Usually, the light will turn off after the cap is properly tightened. However, in some situations, the cap may be faulty.
A small air leak could develop in the cap as it wears, which could allow fumes to leak and cause the gas cap warning light to illuminate on the instrument panel. You can check the gas cap to make sure it’s properly tightened, but if the light does not turn off, the cap will likely require replacement.
According to the Honda Accord manual, a faulty gas cap can eventually cause the Accord’s check-engine warning light to illuminate.