Mercedes-Benz S420 engine light remains on after battery disconnection on Mercedes-Benz S420

Some Mercedes-Benz S420 owners report experiencing issues with the check engine light remaining illuminated even after disconnecting the battery. This persistent warning can indicate various underlying problems, such as a faulty emissions system component or a malfunctioning sensor, like a defective oxygen sensor. Additionally, some owners find that a malfunctioning catalytic converter or vacuum issues may contribute to the check engine light staying on. It is important to note that simply disconnecting the battery may not be enough to reset the check engine light; addressing the root cause is often necessary. Therefore, if the light continues to stay on, it is recommended that owners seek inspection from a qualified mechanic to diagnose and resolve the specific issue.