When the check engine light is on with the engine running, that's an automatic fail for the emissions test — no questions asked. That said, not every state treats this the same way.

That will often coincide with an illumination of your check-engine light, which indicates the OBD-II has detected a malfunction in your car’s emissions controls.

That will often coincide with an illumination of your check-engine light, which indicates the OBD-II has detected a malfunction in your car’s emissions controls.

That will often coincide with an illumination of your check-engine light, which indicates the OBD-II has detected a malfunction in your car’s emissions controls.

That will often coincide with an illumination of your check-engine light, which indicates the OBD-II has detected a malfunction in your car’s emissions controls.

That will often coincide with an illumination of your check-engine light, which indicates the OBD-II has detected a malfunction in your car’s emissions controls.

That will often coincide with an illumination of your check-engine light, which indicates the OBD-II has detected a malfunction in your car’s emissions controls.

That will often coincide with an illumination of your check-engine light, which indicates the OBD-II has detected a malfunction in your car’s emissions controls.

That will often coincide with an illumination of your check-engine light, which indicates the OBD-II has detected a malfunction in your car’s emissions controls.

That will often coincide with an illumination of your check-engine light, which indicates the OBD-II has detected a malfunction in your car’s emissions controls.