Fault Code P0455

[samba3_11]

I bought a '99 boxster about 4 or 5 months ago. The "Check Engine" light has constantly been on for a couple months now. I have had the code read and reset a time or two and the code it is showing is P0455.

I have searched the forums for the fault code and read the other threads that discuss this topic. Specifically, I am referring to the following post by Loren:

P0455 Fuel Tank Ventilation System (Major Leak) - Below Limit

Possible fault cause

- Tank cap missing

- Tank cap seal

- Ventilation lines detached from EVAP canister

- Ventilation line detached from tank

- Ventilation line detached from fuel tank vent

- Break in ventilation lines

Here is where it gets strange and why I created a new thread. My dad is a mechanic. Today, he had it in the shop and he hooked a smoke machine up through the fuel line. He pumped smoke into it and did not see any smoke leaking from anywhere. Then, he thought he may have missed it leaking. So, then he changed from smoke to pressure. During the pressure test, he said it didn't lose any pressure.

I showed this list to him of the possible causes, and he said the smoke test and pressure test ruled out all these possibilities. We are kind of lost as to what could possibly be wrong with it now.

Does anyone have any ideas or know of any possibilities?

Thanks!

[Loren]

Here is how your car checks for a leak (P0455).

"System Description

In order to prevent fuel vapors from entering the atmosphere, an EVAP canister is connected to the tank ventilation line.

Fuel vapors are collected in the EVAP canister. As the EVAP canister can only accommodate a certain amount of fuel vapors, the fuel vapors must be taken in and combusted during driving.

For this to occur, the EVAP canister purge valve opens. Due to the vacuum predominating in the intake manifold, air is sucked up via the purge air line through the EVAP canister. The air sucked up in this way draws the collected fuel vapors with it. American law requires the tank ventilation system to be checked for leaks. For this purpose, the tank pressure sensor and shutoff valve are required."

"Function of Tank Ventilation Diagnosis

In order to check the system for leaks, vacuum is built up in the tank, the system sealed and a test performed to see how quickly the vacuum diminishes again. Pressure conditions are influenced by the vaporization of fuel. Therefore, prior to diagnosis the pressure increase due to fuel vaporization is examined.

Tank ventilation diagnosis is divided into three steps:

1. Measuring the pressure increase due to fuel vaporization. The EVAP canister purge valve and shutoff valve are closed. The increase in pressure is measured by the tank pressure sensor.

2. Vacuum buildup in the system. The EVAP canister purge valve is opened and the shutoff valve remains closed. This causes vacuum to build up in the tank. If no vacuum builds up, a large leak is present, e.g. the tank cap is not screwed on.

3. Vacuum reduction in the system. At a particular vacuum (approx. 8 mbar), the tank vent valve is closed once more. The system is now sealed. Depending upon the speed at which vacuum is reduced,

leaks in the system may be determined."