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Ask Gm Tech (Cam) Your Own Question
Gm Tech (Cam)
Gm Tech (Cam), Cadillac Mechanic
Category: Cadillac
Satisfied Customers: 29516
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I'm getting a PO446 code on my 2008 Escalade and I can't

Customer Question

Customer: Hi. I'm getting a PO446 code on my 2008 Escalade and I can't seem to figure out why. I've replaced everything buy the canister and the code still persists.
JA: Thanks. Can you give me any more details about your issue?
Customer: The one interesting piece is that when I remove the gas cap while the engine is running, the rpms drop way down but then it does recover. If I start putting fuel into the tank, the rpms react but it does recover. If I turn the vehicle off and fill the tank, when I try to start, it turns over for a few times before quitting. After that, it starts just fine and continues to do so until I open the gas cap. It seems the pressure is relieved and it has to re-pressureize.
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Submitted: 1 year ago.
Category: Cadillac
Expert:  Gm Tech (Cam) replied 1 year ago.

Hi there, I am Cam. Can I get your first name?

When you replaced the canister, did you also replace the vent solenoid that is attached close by to that canister?

Also, the canister you bought was about 12" long x 3" x6" or so and mounted above the rear axle?

Customer: replied 1 year ago.
Hi. My name is ***** ***** I replaced the complete apparatus. I also replaced the fuel pressure sensor in the fuel pump.
Expert:  Gm Tech (Cam) replied 1 year ago.

Ok, do you have the part numbers?

Customer: replied 1 year ago.
For what and how will this help? I'll pull them up shortly.
Expert:  Gm Tech (Cam) replied 1 year ago.

Well many people confuse the filter assembly of the vent valve as the canister, so I want to makes are we are on the same page.

Customer: replied 1 year ago.
I did not replace the canister. It should have said "but" and not "buy". The vent valve consisted of the hoses and valve. Why is the gas situation doing what it's doing?
Expert:  Gm Tech (Cam) replied 1 year ago.

The canister is plugged. The gas will be hard to fill because the air and vapours leaving the tank when displaced by the gas flowing in go through that canister and the vapours are captured. When its plugged, the air backs up and causes this. Replace the canister and that should fix it for you .

Customer: replied 1 year ago.
The gas isn't hard to fill. It goes right in and fills up completely. This is both when running and while not. The problem that occurs is the rpms drop drastically but quickly recover when I unscrew the gas cap. The rpms are also affected when I start to fill the tank with gas, but there again, the rpms recover quickly. Once the tank is filled and the gas cap is on, the engine will perform normally. If the tank is full, the gas cap then put on tightly, and the engine is off, it will turn over many times before stopping, but then the next try to start, will turn on right away and then be fine until the cap is opened again. I've read posts about it being hard to fuel, but I've never had that problem.
Expert:  Gm Tech (Cam) replied 1 year ago.

Are you filling with the engine running? This may be expected then as the Engine must be off. Its possible that the issue is made worse by the purge valve located on the side of the intake leaking vacuum when it should not.

Customer: replied 1 year ago.
I'm trying everything to figure this out. I am tying to fill with it running so I don't experience the terrible multiple turnovers for it to finally start. Are you saying the trouble to fill would be when the engine is off? I can try that. It's almost empty.
Expert:  Gm Tech (Cam) replied 1 year ago.

Ok, I think I have enough information to supply a suggestion. You had a P0446, bu your major issue is the hard start only after filling, correct? IF so, this is a faulty evap system , specifically the purge portion. This is the valve on the side of the engine ( replacement document in link attached) that draws the vapours from the canister. This should be closed after staring but I suspect from everything that you have told me that yours is not sealing, so the fuel vapours we talked about are flowing through there when you fuel up causing it to basically be flooded. This is a cheap part, so I suggest you replace this item.


Customer: replied 1 year ago.
I did replace that last year but I do how a multimeter now and wondered if there is a way to test it? Thanks for your help.
Expert:  Gm Tech (Cam) replied 1 year ago.

To test, remove the line off the valve going to the back and remove the electrical connector. With the engine running, see if there is vacuum on that port. IF so then your valve is leaking again. IT must not have any vacuum on the outlet when the electrical connector is removed.

Customer: replied 1 year ago.
Thanks. Im assuming the port to check the vacuum is on the valve. What should I feel on the line going to the back?
Expert:  Gm Tech (Cam) replied 1 year ago.

The port to check vacuum is the outlet port of the valve. Simply checking on the regular service port with the green lid will not work. The hose must be removed from the valve to check this.

Customer: replied 1 year ago.
Thanks. Let me check and see. This was the first piece i replaced when starting to work with this problem.
Expert:  Gm Tech (Cam) replied 1 year ago.


Customer: replied 1 year ago.
I tested it, received suction. Took it to the parts place and bought a new one. I replaced it and cleared the codes. Then after an hour of driving, the engine light came back on. Same code. What next? What do you do when a customer brings their car in for service and this is what goes on? Thanks again.
Expert:  Gm Tech (Cam) replied 1 year ago.

Ok I had figured that the code was independent of the hard start when fueling. The two did not go together.

Now that the purge side is clean we need to look at the vent side. You said it's not hard to fill so it's not completely plugged. If you brought your vehicle to me now I would manually command purge and seal to build vacuum. Then see how long it holds for. Then release it and watch it return to 0. Also knowing how long it takes, I would simply remove the canister, vent valve and quickly blow out the system, then verify the valve opens and closes. Remember the current code is for performance of th vent system and almost always sets when it's plugged.

Customer: replied 1 year ago.
should I just replace the canister or can that be cleaned? Remember I replaced the vent solenoid and hoses already. Thanks
Expert:  Gm Tech (Cam) replied 1 year ago.

I would try to clean it first. Take it off and locate the 3 hoses/ports. Blow air into the smaller 2 ports in turn while tapping on the housing around the third port until you get no dust coming out. Make sure there are no cracks and such. Then install and test.

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