P0446 code and can not fill tank at gas station. I changed out the vent solenoid near the filler neck. While I had the solenoid off, I tried blowing through the hose with my mouth and i seemed plugged (gas cap off). Do these canisters fail often? Do they fail in a plugged state like this?

This is on a 2004 Monte SS Supercharged

Thanks in advance!

 

Yup!
Just resolved the exact same problem with one of my 2000 SS's.
$95 for a new ACDelco canister from RockAuto.
Unfortunately the canister lives on top of the gas tank so the tank has to be dropped out.
I took my time and with a little manpower from a buddy to help maneuver the tank the job took about 4 hours.
Over time the charcoal pellets breakdown and clog the clothe filters near the inlet and outlet ports. Problem is accelerated if the user always over fills the tank, allowing gas to spill into the canister. In some cases they clog with dirt if the car travels dirt roads a lot and the dirt can be blown out. The problem has not been that common. I've owned four gen. 6's, one of which I bought new and this is the first to have that problem, but I think it will become more common as our cars age.

 

Cool! Glad to hear Im not the only one. When you dropped the tank, did you just lower it down on the one side or did you go all the way out? Did you unhook the lines and wires through the trap door first or leave those connected?

 

Dropped it to the ground. Run the car until you have less than 1/4 tank of fuel left.

1. Remove the fuel pump fuse in the engine compartment and run the car out of gas to relieve fuel pressure.

2. Raise the back of the car up and support with jack stands.

3. Remove both rear wheels.

4. Disconnect the three lines (fuel feed, fuel return, and EVAP to purge solenoid) all three on the drivers side by the fuel filter.

5. Disconnect the rubber hose connected to the EVAP vent valve.

6. Unhook all rubber exhaust hangers except the ones by the catalytic converter and pull the exhaust as far over to the passenger side as posible to allow the tank to clear.

7.Disconnect the two wire connections to the fuel pump accessed through the access panel in the trunk. The EVAP and fuel lines can stay connected.

8. Disconnect the fuel filler hose from the rear of the tank.

9.Have an assistant support the tank from below and remove the two bolts securing the two tank support straps (don't bend the straps) and carefully lower the tank which weighs about 35 lbs. with 1/4 tank of gas in it.

10. Remove the 2 hoses and 1 EVAP tube from the canister which is located on top of the tank on the drivers side. Cut the large plastic cable tie that secures the canister to the tank and remove the canister.

Install new canister with a new cable tie from the hardware store and reverse the entire process. Replace the fuel filter with a new one.

 

PO300
PO403
PO405
PO446 ✴︎ ⬅︎ ⬅︎ ⬅︎

All these Codes were triggered by a faulty FUEL TANK PRESSURE SENSOR!

Wait for the Low Fuel Warning before attempting to DIY.
Start engine.
Pull FUEL PUMP Relay ... Let Engine stall to relieve pressure in system.
Remove GROUND Wire from Battery.
With car Raised and SAFETY STANDS securely in place.

Support Tank with Jack.

(I made a "Jig" to attach to the Jack. Sawed the square bottom off from Milk Crate. Drilled holes through Hockey Puck. Mounted Puck to center of Milk Crate with Heavy Duty Zip Ties. Affixed carpet to other side of Milk Crate bottom for padding.)

Lower tank enough to access Sensor atop Fuel Pump.
Unfasten Pigtail from Sensor.
Unclip and Remove Sensor ••• Straight-up.
DO NOT BREAK THE END OF SENSOR OFF INSIDE PUMP!!!

If you need a Charcoal Canister do it when you replace this Sensor.

Removing Fuel Pump Relay to Relieve Fuel System Pressure throws a Code which may require a MIL Light reset.

 

To summarize for anyone who might find this post in the future:

2004 Monte Carlo SS Supercharged

Problem:
P0446 evap code. Can't fill tank at gas station.

Diagnostics:
Removed the vent solenoid in rear quarter area. Found that vent hose going to solenoid could not be blown through or sucked through (gas cap off). This was preventing the tank from venting during fill-up and causing the ECM system to not see a pressure difference when it ran it's EVAP tests. Diagnosed as clogged evap canister.

Repair:
Get tank very low on fuel. Get rid of residual fuel pressure by your preferred method. Disconnect battery.
Remove fuel pump access cover in trunk. Remove both electrical connectors and front and back fuel line connectors (middle hose can stay connected for now)
Remove drivers rear wheel.
Remove 3 plastic rivets on fuel tank to remove heat shield
Separate filler neck at rubber/steel union
Support tank. Remove both rear tank bolt straps.
Lower tank enough to remove 2 large (1 plastic, 1 rubber) lines on side of evap canister.
Lower tank, replace canister and reinstall everything.

I did this on a lift and it took my buddy and I about 2.5 hours and we didn't work very fast. If you are doing it on the floor, I'm sure it will take longer. After repair, no codes and no problems filling tank at all.

 

Congrats on the repair brownc00.

Just a couple things I'd like to add:
1. The rubber hose connected to the EVAP vent valve needs to be disconnected at the vent valve.

2. If you unhook all the exhaust pipe hangers down flow from the resonator, remove the passenger rear wheel and pull the exhaust pipe over to the passenger side it gives enough clearance so you you don't have to drill out the heat shield rivets.

3. The fuel and EVAP lines don't need to be disconnected at the fuel pump. They're the same lines that you can disconnect by the fuel filter. There's just a 3 ft section of each between the fuel pump and the connectors by the fuel filter.

4. If you disconnect the fuel filler tube at the plastic nipple on the rear of the tank instead of the filler neck it gets the hose out of the way. Probably comes off the plastic easier than the metal filler neck too.

5. '04s must be different from '00s, my '00 only had one plastic cable tie wrapped around the center of the canister to hold it. No rubber strap.

 

1. No need to disconnect at vent valve if you disconnect on the side of the canister. I disconnected it there and had no issues.

2. Shield had to come of regardless on my car. It prevented passenger side strap from dropping down. No rivets to drill out, there were all the push in style plastic kind with the removal center.

3. Agreed. I didn't realize that until reassembly buy either will work.

4. No dice there for me. The screw for the hose clamp was pointing up towards the floor of the car. No way to loosen it that I could find.

5. Yes, only 1 cable tie around canister. I was referring to the plastic and rubber hoses on the side of the canister.

 

The Fuel Tank Vent Valve ... located inside the Dr/Side Rear Qtr Panel can be disassembled and cleaned ... and might work again.

NEW Tank Vent Valves supersede OEM models.
If you get a NEW Tank Vent Valve ... you'll need the short "Jumper" that's required to plug-into the New Valve assy -- and -- plug-into the stock end of wiring harness.

OEM Wiring Harness ---------->|[OEM Vent Valve]

OEM Wiring Harness ---------->| Jumper |[NEW Vent Valve]