Q: Will my car pass smog if the coolant is leaking?

It depends. If for any reason, the leak has caused the check engine light (CEL) to come on OR has caused any of the OBD-II emission monitors to fail to register properly, the answer is no it will not pass inspction. An additional complexity is some state inspection protocols require not only emission checks but other "inspections" of the vehicle and certain types of non emission related faults could cause an inspection failure (it depends on what state you are in). I would say if the coolant leak is not visible and there is no effect on the CEL or OBD-II emission testing monitors that the station will electronically access when they test your car, there is nothing to worry about. Nevertheless, of course, it is best to repair a known coolant leak, particularly if it is something that can be readily fixed. If you would like the leak pinpointed and repaired please request a cooling system leak leak diagnostic and and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.