1999 996 Cabriolet. Been battling P0446 for awhile - new purge valve, new gas gap, smoke test sat. Dealer now convinced it's a faulty DME. While I wait for them to order the CORRECT DME, how likely this is actually the cause of P0446?

 

Its almost never the dme. Lots of info if u google the code.

lots of causes from the purge valve, gas cap, blocked purge line, bad charcoal canister, down stream o2 sensors and vacuum leaks.

btw, not sure how a bad dme could even cause this issue but im sure the dealer has a flow chart and at the end of the line it says "replace dme"

if the will refund the cost of a new dme if it doesnt work, let them throw parts at it, i guess.

 

I had a p0446 one time ( customer car) that turned out to the fuel tank pressure sensor on top of the tank.....very unlikely it is the DME...

I certainly would "try" a pressure sensor before condemning the DME... ( DME's are $$$$ ) ....

 

My thoughts exactly - it certainly didn't give me a warm and fuzzy when they ordered the wrong DME...

 

Is there just a single sensor involved in the code?

 

po446 iirr, is more or less a universal incorrect evap voltage error code.

Are there any symptoms, like not able to fill car gas tank to 100% full...?

Here's an easy test to see if there is any voltage in the evap system control cicuit. In a quite garage, remove gas cap and push open the flapper valve with your finger while listening for the 'click' of the reed switch in the filler neck. It makes a distinct click noise 1/2 second after every time its opened/closed, easily heard in a quite garage setting. If no click is heard, check the 7.5amp fuse. for some strange reason only Porsche could answer, evap fuse is listed as 'Telephone' not evap system. Its a 7.5 amp brown fuse in E6 position iirr....

jmo

 

Yea, I have had that fuse blow before, but as I recall it didn't cause an evap code, it caused a code in the "alarm system" and was due to the fuel door lock actuator was shorting...

The fuel door wouldn't lock/unlock, also was causing unable to fill the tank properly/quickly due to no power to the tank vent valve ( also located on top of the fuel tank..)

Yes the "Click test" will verify power to that circuit, it is actually the vent valve/solenoid on top of the tank that makes the "click"...

But iirr it didn't set a code in the "DME" only in the "alarm control unit" ..

Code P0446 is a generic evap code, meaning something wrong with the evap system...

It is a sealed system with " expected pressures" that are sensed by the pressure sensor and reported to the DME..

ANY leak in the whole system can cause the code,( purge valve being the most common........ or fuel cap) but literally any leak anywhere can cause the code...

Aside from any leaks, the pressure sensor monitors for expected pressure changes/or non-expected pressure changes due to leaks or purging of the fumes, but if the sensor is its self faulty, then the DME will receive erroneous reports on the evap system and flag a fault code....