one of my buddy who have 2003 Silverado 133,000 mileage just got engine light on. Scan it and show P0455 it is something from evap I cant remember. See if yall can give me some hint and solve this problem.

 

First thing any shop will check with that code is to make sure the gas cap is on good and still sealing properly. If that's not it then it might be one of the purge solenoids is bad. My truck had a bad purge solenoid when I bought it and was getting the same code.

 

Many thanks I will check tomorrow and replace both.

 

Hey my friend jason info me that when he clear the code. It was all fine and drove alot for 2 weeks include long trip about 8 hours. Never had problem. Until today finally came back engine light on. Scan it ans show it's p0455 code same one.

 

So did you replace them both?

 

If so, maybe a hose is leaking, or it's the wrong gas cap.

 

Never replace since code went away for 2 weeks and thought it was fine until now. I want to know which one will need to replace. I don't think it will be hose leak?

 

P0455 indicates EVAP large leak detected. Not usually a purge solenoid....More likely a Vent Solenoid. Smoking the system is the only way to find out for sure.

 

Or use a Miller pump and fill the system while observing the vapor pressure sensor on a scan tool...a little soapy water in a spray bottle helps some times also, pump up the system with the low pressure Miller pump, spray suspect areas with the soapy water and look for bubbles NEVER pressurize the gas tank and/or EVAP system with shop air, as many parts can get damaged. I've seen more than one vapor pressure sensor pegged out because some schmuck stuck a shop air hose in the filler neck and let er rip

 

I use the GM essential tool EVAP cart but I guess not everyone has access to those. Most of the time with a large leak the gas cap has to be left off, vent solenoid, or a hose off. EVAP leaks are hard to diag in the driveway.