Emission Control Leak on 1997 Ford F-150

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Check engine light goes on and sometimes off.When light went on and stayed on I hooked up my OBD tool and the code was PO455 EVAPORATOR EMISSION CTRL SYSTEM LEAK (large) 1of2 Same code for 2.What needs to be replaced or checked out. Thanks for any help!
(2) Answers
(1) Comments
The most common cause for an evap leak is the gas cap. If the gas cap is on correctly then it may be a good idea to replace it and clear the code. I would recommend a factory gas cap. If the light comes back on with a new cap then the evap system will need to be checked for leaks using a smoke machine.
I have seen some damaged EVAP lines on Saab's causing a code p0455. The lines can become damage near the rear of the front subframe. The best way to find an EVAP leak is to use a smoke machine. This special tool will pump smoke into the EVAP system. With the vent and purge solenoids closed, any visible smoke should be coming from the source of the EVAP leak.