Q: Muffler delete, check engine light

It is illegal in almost all jurisdictions to delete the muffler from your vehicle. Of most concern, the deletion will negatively impact your health, and that of your passengers, as excessive noise is guaranteed to damage or degrade your hearing. The wisest course is to re-install the muffler. With regard to the check engine light, there might be a cause and effect relationship between the removal and the illumination of the check engine light but that will depend on exactly which OBD-II diagnostic codes have been set. A muffler creates a small amount of back pressure and it is conceivable that the normal range of operation of an upstream sensor has been affected by the reduction in back pressure. Still, that possibility is speculative and the actual circumstances can only be determined once the code(s) are read and whether those codes even implicate a potentially relevant component. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you. And, please keep YourMechanic in mind for your maintenance and repairs.