Help! with Fuel Tank Vent System

[Danyol]

Guys,

I've been helping a friend with his 2002 TT and a very frustrating (intermittent!!) P0455 DME code. He needs to get through emissions inspection, in AZ they just connect to the OBDII port and the system won't show a "ready" state so it will fail.

We've seen several references to what the problem could be, just trying to narrow it down. We have the DME manual, shop manual (I thought it was complete) and completed a lot of research on the forums. Some things that will help,

- We need a full drawing of the tank vent system with the location of components; where is it in the manuals?

- References online indicate the simplified system for detection is as the attached. Where is the pressure sensor "5" located at? We've looked around the tank and the evac canister, doesn't appear to be anywhere near.

-We hear some kind of pump that comes on with the ignition, is that part of the evac system, where is it?

[JFP in PA]

P0455 is the "large vacuum leak" code for the EVAP system; usual suspect is the gas cap..................

[Loren]

P0455 further diagnosis...

1 Check tank cap and seal

- Check whether the tank cap is present.

- Check whether the tank cap is correctly screwed on.

- Check whether the seal is damaged.

2 Check ventilation lines on EVAP canister

- Remove front right-hand wheel housing liner.

- Check whether ventilation lines are attached to the EVAP canister.

3 Check ventilation line on tank

- Remove battery.

- Remove battery cover.

- Check whether ventilation line is attached to the fuel tank sender unit.

4 Check ventilation line on tank vent

- Check whether ventilation line is attached to the EVAP canister purge valve.

5 Check ventilation lines

- Check whether ventilation lines are:

- cracked

- broken

- interrupted

6 Check EVAP canister purge valve

- Remove front right-hand wheel housing liner.

- Clean EVAP canister in the vicinity of the ventilation lines.

- Detach the ventilation line to the EVAP canister purge valve at the EVAP canister (connection with protective cap).

- With special tool 9160/1, generate a vacuum of 200 mbar (0.2 bar).

If no vacuum can be built up, replace the EVAP canister purge valve.

[logray]

-We hear some kind of pump that comes on with the ignition, is that part of the evac system, where is it?

If it's a brief whirring noise, that noise is the fuel pump.

[Danyol]

Guys,

Thankyou!

- The gas cap has been replaced a couple of times

- Trying to follow DME diagnotic procedure on leak checking but have no diagram.

- The car has spent time at an experienced Pcar shop, exercised all the system diagnostics using a Porsche tool. Everything appeared to act normally during all the actuation tests.

Loren,

"Check ventilation line on tank

- Remove battery.

- Remove battery cover.

- Check whether ventilation line is attached to the fuel tank sender unit."

On the turbo, the connections are under a square cover in front of the differential. Are there connections under the battery tray we cannot see, in particular, where is the pressure transducer?

Thanks!

Edited April 30, 2012 by Danyol