How can I tell if my ceramic coating has failed or is just contaminated?

Start with a thorough wash and chemical decontamination. If hydrophobic behavior returns, the coating was most likely masked by contamination rather than gone. If water behavior remains weak and the surface also shows reduced slickness and noticeably harder cleaning, the coating may be significantly worn. Compare the suspect area with a less exposed area such as a lower door or door jamb; a large difference in behavior after the same cleaning points to localized wear. Inspect before reapplying, because a worn coating usually needs surface preparation first. If performance returns only briefly and fades again within a few washes, the coating is probably thin or worn and may need a topper or reapplication.