I'm new to the forum. My engine light has been on for almost 2 years in my 2008 Silverado Z71. The error code shows it is P0455, large leak in emission system. I've replaced the valve solenoid, the purge canister valve, the valve filter, all the valve hoses and even the gas cap, but the engine light remains on. I have noticed that the past two winters, when the temperature dips way down, the engine light will turn off but once the temps go back up, the engine light is back on. Does anyone know how I might be able to finally resolve this issue?

 

the test is temperature dependent. it doesn't run when the temp is to cold

pretty hard to resolve this without testing equipment.
the test runs as such:
with the engine running
the pcm closes the vent valve, opens the purge to allow manifold vacuum to create a low pressure on the system. the fuel tank pressure sensor monitors the pressure and expects to see a calibration amount of pressure drop. if this does not occur the code sets.

so you need:
- a evap leak tester to verify the system is sealed.
- a scan to tool to verify the purge is opening and vacuum is reaching the fuel tank pressure sensor
- a scan tool to verify the ftp sensor is reading correctly.

 

Thank you. I'll do that.