Cause 1: the film itself
Aromatic urethane and PVC film turn amber under UV, fastest on white and silver paint. If the whole panel has an even yellow cast and the film is a few years old, that is the film. It will not clean off. It needs removal and replacement with a UV-stable film. Ceramic Pro Urban and Ceramic Pro PPF are warrantied against yellowing for 10 years and lifetime respectively.
Cause 2: contamination on top
Road film, tree sap, love-bug residue and sprinkler minerals build a brownish layer on any surface that is not washed and decontaminated. On film it looks like yellowing. A decontamination wash with iron remover and clay takes it off, and a Ceramic Pro coating over the film stops it coming back.
Cause 3: edges only
A dark line along the edge of each panel, with clear film in the middle, is dirt collecting under an edge that was not wrapped. Cleaning helps briefly. The fix is film with wrapped edges.
How to tell
Bring the car in. Ten minutes under the lights with a clay bar on one spot tells us which of the three it is, and what it costs to fix.
