Undefined Fuel-reserved For Proprietary _top_ May 2026

These are unique to brands like Ford, Toyota, or BMW.

The most common reason for seeing this message is . undefined fuel-reserved for proprietary

In many cases, proprietary fuel codes are triggered by a loose or failing gas cap. It’s a simple, "low-tech" fix that often clears "proprietary" EVAP codes. These are unique to brands like Ford, Toyota, or BMW