adrian1

I am Diagnosing a friends 2009 Cayenne GTS with a p0455 code( Large Leak Evap) . The Tank Vent Valve(948.110.020.03) by the right valve cover and the Gas Cap had been replaced and did not fix the problem. Any thoughts on how to diagnose this code. Did a smoke test and it did not show any obvious leaks.......

mudman2

Apart from the error code what are the symptoms ? Filling up with gas with engine running ?

XR4Tim

Is your leak detection pump working? How about your vacuum pump? I vaguely remember something about the LDP not working if the vacuum pump has failed on 957s.

adrian1

No symptoms at all. Running fine, just after couple days he says the light always comes back on. It has 58,000 miles on it.

adrian1

Where would the Vacuum Pump and Leak Detection Pump be located?

XR4Tim

The leak detection pump is on the carbon canister in the rear wheel well (left side, I think). The vacuum pump is on the back of the bank one (right side) cylinder head.

adrian1

Ok, I am at the the LDP, I disconnected the line going from the intake to LDP and put vacuum to it. -8 P.S.I. and seems to drop within 1-3 mins; not sure if this a real "leak".

XR4Tim

I think that's normal. If I'm reading my diagrams correctly, you may need to pinch off the hose going from the LDP to the carbon canister first in order to really check for leaks.

adrian1

Its disconnected from the LDP to Intake. I plugged the hose where I took it off the LDP and vacuumed from the hose by the engine and thats where the drop was. I also think that much drop would not cause p0455 (large leak). Now I'm going to do a smoke test from the other hose off the LDP to the canister.

adrian1

No leak there either, don't know where else to look...

XR4Tim

You're correct, that would not trigger a "large leak" code. Did you put vacuum to the pump itself, or to the line at the intake? If you applied vacuum directly at the pump, you should check the line from the intake to the LDP, and see if the line itself holds vacuum. Any leaks in that line can cause this problem.

When you did your first smoke test, did you smoke it from the filler neck?

adrian1

Ok, there are no external leaks whatsoever in this system and even holds 1/2 psi for a bit which shows no large leak. i let the smoke machine do 5 tests continuously. Either LDP is pump continuously making the DME trigger a p0455, or theres a problem with the vacuum pump on the back the right head. I don't understand what is its operation in the evap monitor system.

The DME triggers the LDP with a ground and closes the Tank Vent at the front of the engine to check for leaks. When the upper diaphragm fills with pressure it can't pump anymore. This is sent by the Diagnosis wire to the ecm showing how many times it pumped (By A Reed Switch) in order to check for "Very Small", "Small", or "Large Leak". A Large leak would let the LDP Activate Continuously due to no pressure being built up.

Now I am not sure how the vacuum pump comes into play here or what is its operation and please correct me if I am wrong with anything.

Thanks!

XR4Tim

That's all correct. I seem to remember that the vacuum pump supplied the vacuum to the LDP on the 957s. I could be wrong - it's been a couple of years since I've done this diagnosis.

adrian1

Oh, I thought it comes from the intake manifold vacuum. I also just found out that the other shop replaced the LPD

So Things that have been replaced:

1.) LDP
2.) Gas Cap
3.) Tank Vent Valve

Plus, No External Leaks. Holds 1/2 P.S.I. With Smoke for over 5 mins.

adrian1

You are correct the Vacuum Pump does supply vacuum to the LDP. I T'd into that line and see that im getting 10 p.s.i. but if i relieve it, it takes quiet a few seconds to come back on. I am wondering now if the Vacuum is not enough to supply the LDP while its pumping pressure into the EVAP System.