1999 Grand Marquis code P0455

Asked by May 25, 2019 at 01:23 PM about the 1999 Mercury Grand Marquis

Question type: Maintenance & Repair

Check engine light is on. When I took
this car to get smogged two years
ago, the smog technician said that it
passed with flying colors. A couple
months after that, the check engine
light popped on one cold morning
going down the highway and has
never gone off since.
My car was scanned and the
following code popped up: P0455 -
Evaporative Emission System Leak
Detected (gross leak/no flow)

I changed the gas cap. Light is still
on. Does anyone know what else it
could be??? I feel like I have no idea
what step to take next...

I live in California. Smog laws are
strict. If I can’t get the light off, my car
is basically unable to legally be driven
- Which is such a shame because it
still runs great despite the fact that
the light is on!

Please help if you think you can!!!

2 Answers


Since the engine runs fine I'd suspect a stuck closed purge valve. If the "no flow" was being caused by a broken or disconnected vacuum hose for the EVAP system you'd have problems with the engine running poorly. Hope that helps! Jim


Look up the EVAP system online for a diagram. This could be caused by a hose leak. You may need a smoke test to find the problem.

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