OBD-II code · Emissions / Engine
The fuel tank vapor system is losing pressure through a leak small enough that only a precise test finds it. Classic causes: a worn filler-neck seal, a hairline-cracked vapor hose, or a vent valve stuck open. The gas cap is on the list but is rarely the whole story.
Tighten-or-replace the gas cap, clear it and hope. When the code returns, the next guess is a $500–$900 EVAP canister replacement — for a $20 hose.
Typical guess-and-swap cost: $500–$900 (canister) when the leak is a $20 hose or a $15 filler gasket
Smoke test. Real diagnostic smoke pumped into the EVAP system makes a very small leak visible in seconds — a dripping filler neck, a perished hose by the tank. This is a 20-minute test with a $60 machine, not a parts lottery.
Mobile service in Canyon Lake, San Antonio & Austin. Written report with root cause — see a sample.