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1997 Boxster with 1999 3.4 swap + 996 DME remap - error codes P0447 and P0453


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I need help clearing two codes due to a 3.4 engine transplant in a 1997 986 I just purchased. I have two OBD codes P0447 and P0453 related to the the shutoff valve and fuel tank pressure sensor used in 1998+ cars. I found several other posts noting 1997's do not have wiring nor support the 1998+ fuel leak check hardware so I am taking the challenge to find alternatives to clear them for good.


I have searched high and low and unable to find signal details the 1997 DME flashed with 99 996 3.4l map. Has anyone measured the voltage from pin 7  to ground on:


1997 DME remapped with 3.4l map  (I measure a little over +6V for DME pin 7  to ground when nothing is connected)


I thought I could easily clear the P0447 (open circuit) by simply connecting a 996-605-201-01 shutoff valve with a 12V source to pin 7 on the DME since both 97 and 98+ DME wiring diagrams show pin 7 as "AAV VALVE." However, after installing, P0447 goes away but code P0448 (short circuit) appears. The valve resistance is ~25.5 Ohm and toggles open and closed with a 9V battery so I don't think it is a bad valve. What is the pin 7 current or voltage signal the DME  is expecting? 












Edited by xmac
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  • 1 month later...

Answering my own question:


In case someone needs it in the future, the shutoff valve needs to be connected to a switch 12V source on one end and the other into the DME pin 7 (yellow/brown) wire,  not to ground as I had it. It appears there is ~-6V on the DME that reduces the voltage on the solenoid to a net of 6V (if a +12V source is used) and when the evap system pressure test happens, it adjusts the -6V to 0 so that the valve now sees a full 12V and actuates. 


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