Does anyone know how test the evap system? I have an engine codeP 0455 large leak detected. I don't know where to start.

 

Drive around for a bit. Stop and take off the fuel cap. If the fuel cap does not purge then you definetly have a leak. You need to change your fuel cap. If that does not fix the problem then you need to replace the rubber hoses at the canister. These are located in the engine compartment.

 

Don't mean to jack your thread , But hey greenmachine? Buy purge you mean hear air swoosh when the cap is opened correct? I never hear anything since I've owned it for 6 years and I don't have any codes. Is it possible the cap is bad ?

 

Ideally, you use a smoke machine to test for evap leaks. Since most guys don't have that little $1000 piece of equipment, all you can do is physically inspect fuel cap, solenoids, charcoal canister and all connecting hoses inch by inch. Bad fuel caps (or loose, missing) are the #1 cause for evap leak DTC's, but I've seen plenty of cracked lines and melted purge valves. Also see lots of stuck vent solenoids in dusty areas.

 

Exactly

 

Just fixed my p0455 code that I've had for going on 3 yrs yesterday. For some reason there is a hose that does a 180 out of the canister and connects to a fitting in the frame rail. You can't see it but upon feeling the line I found it split wide open. Replaced code gone today. Actually I also had a p0138 O2 code but lite off today either way.

 

x2

I would check the vacume hoses under the hood for cracks first (since they are easy to access).

If they look good - no problems, move to the Evap canister. It is easy to pull down and check the hoses. If you are throwing a big leak code though... you should be able to feel it.

I was about ready to give up on my evap leak and pay a shop. I'm glad I check the canister connections. Cost less than 10 bucks in parts and an hour of my time to fix. I feel much better knowing that I fixed it.

Good luck,
Cartman

 

Was your canister under the cab or in the engine compartment? I have a round and square canister under the cab.

 

Passenger side rear of cab square.

 

That's it. Should be on the passenger side under the cab.

I just unbolted the bracket and took them off so that I could get a good visual inspection on them. It should only be 3 or 4 bolts.

Cartman