Large evap leak --check gas cap that it is on --look under truck at rear of fuel tank by spare tire and check the evap canister and hoses the following link will assist you
https://www.obd-codes.com/p0455 How to Fix Check Engine Light P0455 Emissions Purge Valve Replacement How to Fix Check Engine Light P0455 Emissions Purge Valve Replacement
SOURCE: code p0455 evap emission (large)
have the gas cap tested or just replace it, then disconnect the battery for 5 minutes to reset the code, then drive it for a few miles and see if problem comes back, if it does a trip to the dealer is in order, as this may be covered by your emission warranty which is good for 70,000 miles.
SOURCE: P0449 and P0455 error code 2008 2wd gmc envoy
P0449 - Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction
P0455 - Evaporative Emission Control System Leak Detected (no purge flow or large leak)
Both are refer at EVAP system; other EVAP DTCs: P0440 - P0441 - P0442 - P0443 - P0446 - P0453 - P0455 - P0456
This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.
Symptoms: You likely won't notice any drivability problems.
Causes: most likely means one or more of the following has happened:
A loose or improperly affixed gas cap
A non-conforming gas cap (i.e. not factory/original brand)
Other leak or damaged piece in EVAP system
Possible Solutions: the most common repair is to:
Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
Otherwise, replace the gas cap, and/or
Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary
Hope helps.
SOURCE: engine light code p0455 chev monte carlo
Hello,The problem is that the EVAP system is not able to achieve or maintain vacuum during the diagnostic testThe control module tests the evaporative emission (EVAP) system for a large leak. The control module monitors the fuel tank pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running the test are met, the control module commands the EVAP canister purge solenoid valve OPEN and the EVAP canister vent solenoid valve CLOSED . This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the control module commands the EVAP canister purge solenoid valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, the PCM will set the code you now have.So, you either have a stuck open purge valve, a stuck open vent valve, a false reading fuel tank pressure sensor, or a cracked/broken EVAP line.
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