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Recently, on my 98' Boxster (mileage 90 K) the CEL came on and from my Durametric reader, code P0446, Porsche fault code 95 [shutoff valve activated / charcoal filter] was displayed. Can anyone explain what this means and what do I (from a DIY perspective) need to do? Thanks!

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You need to get the full set of Porsche service manuals including the OBDII and Diagnostic manuals. You can contact me about that. As to your code see below. I copied most of the information for you and attached the pages from the DME 5.2 manual. Obviously this is only for educational purposes.

P0446 95 EVAP Canister Shutoff Valve (Function) – Below Limit



20 93




95 EVAP Canister Shutoff Valve (Function) – Below Limit




The task of the shutoff valve is to seal the purge air line to the EVAP canister during the fuel tank leak test.


Diagnosis conditions


– Oxygen sensing system active


– No secondary air


– No secondary air diagnosis


– Air mass < 30 kg/h


– Engine running


– Vehicle speed = 0 km/h


– Intake air temperature between –12 °C and 60 °C


– Battery voltage > 11 V


– Engine load < 2.4 ms


– The vehicle must not be at an altitude of above


2448 m


– Time elapsed after engine start-up > 990 sec.


– No faults in: Throttle position sensor, idle air


control, load sensing, misfire detection, vehicle


speed, EVAP canister purge valve, idle air control


valve, mass air flow sensor, voltage supply,


pressure sensor, shutoff valve and engine




DTC No. Fault conditions Fault area


P0446 Below lower limit – Purge air line blocked


– Flow resistance of EVAP canister too high




Fuel tank ventilation can be activated with the Porsche System Tester 2 in the Short test menu.


On-Board Diagnostic Boxster Troubleshooting


1999 Supplement 3 P0446 - 1


System Overview




1 – EVAP canister purge valve


2 – EVAP canister


3 – Purge air


4 – Tank


5 – Pressure sensor


6 – Shutoff valve


7 – Operating purge valve


8 – To intake manifold


9 – Vacuum control valve




Troubleshooting Boxster On-Board Diagnostic


P0446 - 2 Supplement 3 1999


Diagnosis Procedure


1 Check purge air line for blockage.




Repair purge air line.




Replace EVAP canister.




Not OK


On-Board Diagnostic Boxster Troubleshooting


1999 Supplement 3 P0446 - 3


1 Check purge air line for blockage.


1. Remove front right-hand wheel housing liner.


2. Detach purge air line (connection face up) from


EVAP canister.


3. Blow through purge air line with compressed air.


Troubleshooting Boxster On-Board Diagnostic



986 DME 5.2 P0446.pdf

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  • 6 years later...

There is a 'shut off' valve with electric plug on it, top front of charcoal canister which I changed along with the pink valve on top of canister (maybe called purge or vent valve) a double type valve about 3 months ago. CEL still comes on. That's why I am really interested in this blue thing on the side of the canister. It does NOT have an electric plug to it.   I disconnected the pipe top from the pink vent thing and the bottom with the blue plastic type round valve set in the middle of this length.  I held the pipe in my hands and can blow each way past this valve with ease. I would have thought I could only blow one way as a kind of a one way valve thing but NO.  Is the thing GOOD or BAD? Whats this for?. Why is it there?. What is the name of the thing?. I seem to remember someone said it is a 'check valve' but it doesn't seem to check anything only my patience as far as I can tell. I put the part # on google NOTHING. Oh yeh some bloody oil well in Texas somewhere came up. Very helpful lol.

Edited by Hurdigurdiman
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