1999 Chevrolet Metro P0455 Code: Fuel Vapor Leak Detected Despite Smoke Test and New OEM Gas Cap
My 1999 Chevrolet Metro has been experiencing the same issue for over a year, consistently showing OBD2 fault code P0455. After failing my California smog check, I enrolled in the Consumer Assistance Program (CAP), which covered diagnostic costs. The repair shop initially suspected a faulty gas cap, but I had already replaced it with a brand-new OEM cap from the dealership. I’ve also tried two different aftermarket caps without resolving the issue. They performed a smoke test to detect fuel system leaks and found no abnormalities. Despite the negative smoke test result, I can clearly smell fuel vapor inside the cabin whenever I refuel. This raises concern—how is there a leak if the system appears sealed? The shop charged $200 for diagnostics, and California CAP covered this cost. They only performed a reset of the MIL (Malfunction Indicator Lamp) and completed a drive cycle to retest the vehicle. The car has never failed on hydrocarbons or other emissions tests—only the P0455 code persists. I’ve been told that the system runs a test during startup when the engine is cold, but the MIL activates whenever the car is running, especially during deceleration on the freeway. This behavior contradicts standard operation and suggests an underlying issue with vacuum or pressure integrity in the evaporative emission control system.
If you can smell fuel vapor but the smoke test shows no leaks, it's likely that there's a component failing to maintain proper vacuum or pressure within the EVAP system. This could result in fuel vapors entering the intake manifold when they shouldn't. While not an extremely complex issue, accurate diagnosis and repair typically cost more than $200—especially for older vehicles like the 1999 Chevrolet Metro with aging seals and hoses.