P0455 Smoke test from vent hose behind rear bumper - 986 Forum - The Community for Porsche Boxster & Cayman Owners

I need some help trying to solve a p0455 (tank vent system, major leak) code on a 2000 base Boxster, Tiptronic. I'm smoke testing the evap system and the only leak is from a vent hose (?) behind the rear bumper. Testing procedure: applied 12v supply (old wall wart with alligator clips) to the purge valve below left intake to activate it. Removed its hose from just past the throttle body and attached my smoke machine (0.5psi pressure) into that hose. I removed inner front right fender shroud to see the carbon canister and lines, and the battery/tray to see the top of the tank connections. I'm testing in a pitch black garage with a handheld work light to see the smallest traces of smoke. The only smoke I detected was coming from the bottom rear corner of the bumper. Scratching my head, I removed the cover and it is coming from this line, which is open to atmosphere. What is this, and what does it connect to at the other end? Can anyone point me to a diagram? It disappears into the area above the exhaust on the left side of the car, hidden up above the heat insulation. So I can't easily trace it without removing a bunch of things. Any idea what is happening here? Is my testing procedure incorrect and I'm letting smoke into something I shouldn't? Is there a failed component somewhere that is letting things flow into this line? Should it be capped? I temporarily plugged it to do the test again. I can't find any leaks anywhere else. Help!

Can anyone tell me what that pipe is behind the rear bumper? Further info: I was also trying to track down two other codes, P1128 and P1130. A smoke test of the intake found a huge hole worn through the accordion section of the brake booster vacuum line. I temporarily wrapped that with electrical tape while a new one is on order. I ended up leaving a rubber vacuum cap over the end of the pipe behind the bumper, to see what would happen. Without knowing its function, it just seemed odd that any line would be open to atmosphere. So far I've put several hundred miles on the car and none of the three codes has recurred, and no codes are pending. In the past, all three would come back within 20-50 miles of driving. The car is currently running great. I'd still like to understand what the situation is/should be with the line behind the bumper.

I believe that hose runs from the rear bumper up to the valve housing in the right front wheel well. See my prior post for info about the ORVR/EVAP system for pictures and a system diagram. I think it is hose “E” in the pictures. The system info I have access to doesn’t describe that hose end point very well. It just says “Scavenging pipe to the rear”. http://986forum.com/forums/boxster-general-discussions/82728-coke-bottle-noise-fuel-filler-howling-noise.html From my research, that hose at the rear bumper is to remain open to atmosphere at all times. It is the source of fresh air to let vapors from the canister be sucked to the intake when the valve on the intake is open. The fact that you saw smoke come out of it shows it’s connected from the intake, through the canister and the valve body. To verify you could disconnect the line at the wheel well end, apply smoke or compressed air there and see if it comes out at the bumper. I’m having a hard time explaining how capping it made your P0455 issue go away and why you haven’t developed the coke bottle noise through the vent hose at “D”. I don’t have a good understanding what triggers P0455.

Thanks, that is super helpful information! Somehow I didn't come across your older post about the EVAP system during my searches. I had eventually figured out that the line to the rear bumper goes to the carbon canister/valve housing (# 8 in this diagram), but haven't had a chance to do more testing yet. It took almost 500 miles, but it did eventually throw a code for incorrect EVAP pressure with that line capped. That is helpful to understand that it is an air intake line rather than a vent. I guess my next step is to test the shut off valve, tank venting valve, and vacuum limiting valve for proper operation (all the ones near the carbon canister). I only came across one other post of anyone mentioning smoke coming from the rear bumper during a smoke test, and it was immediately dismissed as caused by someone not knowing what they are doing, so I'm still curious if my smoke testing method is correct. Do any of the other valves need to be activated during the test other than the purge valve below the intake? I'm doing all of this with the key off, so nothing else is powered. I still haven't found any other leaks during smoke testing. Anyone know if any of these symptoms point to failure of a specific component? One of the numerous valves? The carbon canister itself? I need to get this thing through smog testing very soon.