Lost power in an '04 XG350L

Recently the "Check Eng" light came on in our 2004 XG350L. It stayed on for a couple of days, and went out. Right after that, the car would hesitate on
acceleration from a dead stop and sort of stumble as if it was not getting any fuel. The car has 32,297Mi on the clock and has always been treated with love and care. I only use Union 76 (Top Tier gas) or Conoco (same company) 87-octane and usually tank-up from the same service station. Service has been done religiously by the dealership since the car was purchased. My wife took the car in today and they found a diagnostic code of "P0446" - a code that is NOT in the manual. The tech called the TECH LINE and was told to clear the code and do EVAP test 2x. The car passed both times. He then purged cylinder connectors - turned out OK at this time. No other codes found. Then there was this sort of cryptic code at the end of the invoice - "39466RPO .3 N15 C15". So, any thoughts?
--

Carl


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Your car's evaporative emissions system tests itself with engine vacuum. There's a valve on the charcoal canister which closes and a purge solenoid on the engine which cycles to vacuum the system. The code P0446 typically means that there's too much vacuum in the system during non-test times. This usually means that one of the following has occurred:
The close valve (the one on the canister) stuck closed, causing the system to not be able to vent properly.
The purge valve stuck open, causing constant purge (and more vacuum than intended).
There is a restriction in the venting of the canister. This could be in the canister itself, in the vent filter, or a clogged hose.
The fuel tank pressure sensor was inaccurate, causing the computer to be fooled into thinking there's too much vacuum in the system.
I've seen all of the above. What's worse, running the evap test may not make the code reoccur. I'm surprised tech assistance advised him to diagnose the problem in this fashion.
Basically, what he did, was check the system the way they requested as well as check some of the connectors to verify good contact, and didn't find any problems.
If there's a problem still there, you check engine lamp will likely come back on within the week.
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That's a warranty labor operation code relating to the canister purge valve.
There's a huge TSB pertaining to P0446 and a flowchart within to diagnose it. I see it a lot at work (dealership) and usually it's a canister close valve, purge valve, or tank pressure sensor that's kicked the bucket. Your light will be back on soon since they didn't find and replace the faulty component judging by the labor op code above. It can be tricky because the various sensors and valves can intermittently glitch. If you head back with a P0446 again, point them to TSB 04-30-001.
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