Torque Pro shows Code P0446
–P0446 is triggered when the ECM has detected a short in the circuitry to activate the vent control valve or the EVAP system failed to maintain the vacuum during the active EVAP leakdown test.
No shorts in the wiring folks.
-Both Purge and Vent solenoids made substantial clicks when I commanded them on and off. This put them on the back burner.
-When I closed the vent and opened the purge valve 20% I heard a sucking noise from the filler door and the tank pressure sensor noted ZERO change… Dead Steady at 6.6in Hg.
Okey Dokey. Off to O’Riley for a Stant filler cap to replace the knackered cap on the fill pipe.
New filler cap installed. Cleared the DTC codes. MIL re-illuminated on the way home. *** is going on here…
OK… Peeling the Onion…
-GM Tech2 still shows 6.6in Hg no matter what the state of the EVAP valves. No sucking noise from the filler neck anymore so the cap really was worn out. I can now make the engine stumble from vacuum being pulled on the tank with the purge open and vent closed… The pressure sensor is reading rock steady at 6.6in Hg.
-Change the EVAP tank pressure sensor with a brand new GM sensor from the dealer in Wells River… Don’t trust China made crap and this sensor is in a really unpleasant location.
Tip for anyone doing this sensor. It’s just like a MAP sensor. The tank pressure sensor is press fit through the top of the sender but there was no need to drop the tank or lift the bed… at least on my 2005 extended cab 2500 HD. I could access and change this sensor by feel reaching up between the frame and the bed side. I made sure there was no crud on top to drop in the tank and kill the fuel pump. A backpack blower with an elbow would’ve made quick work of any loose dirt.
No more sandblasting the rockers and bed corners.
My first Blackstone UOA showed much more silica than I would like to see.
$350 Chinese knockoff with CANDI and the mods referenced by the SAAB guys.
– I replaced the dodgy DC-DC converter with a quality Japanese or Korean unit. I’ve forgotten which country it came from.
– I also replaced the SOP MAXIM RS232 <–> TTL chip with the correct part. Some Asian units have the MAX202, like mine, instead of the MAX232. $0.32 from Mouser along with some other components to make a $25 order. Floated it off with a cheap hot air pencil and tweezers. Then soldered on the replacement. Most of the new ones actually have a real Maxim MAX232 now.
My spares ride in some old PCMCIA hard plastic travel shells and a Ziploc freezer bag to protect them. You can find inexpensive card cases on Evilbay by searching for “PCMCIA Card cases”. I also keep the cables and CAN-DI in Ziploc freezer bags.
After MY 2013 you’ll need a Bosch MDI and GM GDS on a laptop. You can run Tech2Win and GDS on a cheap used laptop using the MDI as the vehicle interface so…
I would highly recommend finding a cheap obsolete business class laptop with USB ports and PCMCIA/CARDBUS slot. The DELL D620 D620 D820 & D830 are in the $100 price range, came from Dell with Windows XP but will run Windows 7, and have real DB9 RS232 serial ports in addition to USB2 & CARDBUS slots. My ancient 14 year old beat to death HP NX7400 works quite well for burning cards as well but it doesn’t have available Windows 7 drivers from HP and has no RS232 port.
To quickly burn linear flash cards for the Tech 2 in a CARDBUS slot in your laptop You’ll need some obsolete software from the long gone Elan Systems company called Memory Card Explorer. You can’t buy MCE anymore. If you need a virus free copy PM me. The SAAB guys have a pretty good Tech 2 WIKI that includes MCE binary images of Tech 2 PCMCIA linear flash cards.
Mine is running the last flash image available from GM… 33.004 GM North American Operations. It works on my 2009 Impala, 2005 Silverado T800, and 2000 GMC C2500 T400. It should’ve worked on a 2007 T800 with a good CANDI box…
FYI: I’ve read that some mid 90’s GM vehicles need earlier card versions to access all functions. It seems that GM neutered the diagnostic functionality for the older vehicles in later releases.