Oxygen454

Battery is back up on power after sitting on a smart charger. I must have drained it down from sitting with the doors open and lights on.

Cars status otherwise has not changed. Same codes are there, P0446 and P0300.

Would it help to post the freeze frame data for both codes?

Oldblue

https://www.obd-codes.com/p0446


Check the wires to the vent valve for corrosion or broken wires

Oxygen454

I will see if I can find a schematic. A resistance test might help as well.

I just noticed something from the freeze frame data...

​​​​​​Test failed with the FTP showing -7 inches of H20 and 2.8v
Test Result: Excess PressureIf all the lines are not obstructed and the charcoal canister is in good condition, not contaminated, not plugged, is this a physical issue or electrical?

donbrew

The test relies on the vent being OPEN. It is "Normally Closed". And the purge being CLOSED. It is "Normally Open".
I don't know what you expect a wiring diagram to tell you. There are 2 wires, one goes to the fuse box the other goes to the ECM. The ECM controls the ground signal.

Oxygen454

I was wondering if the wire colors change from under the car to the ECM. (My old cavalier changed wire colors 3 times before it got to the ECM from on of the sensors I had.)

So, I was reading back through all these posts and reading the shop repair procedure and I realized I never checked the tube going from the canister vent solonoid to the filler neck. Also my gas cap could have issues.
I have never seen the fuel tank not under vaccum, the fail was from too much vacuum. Also the vacuum is pretty high out of spec iirc.
I'm going to see if there is a blockage in the vent tube and somehow check the gas cap. This car might kill me before I figure this out but I'm going to die trying 😂

donbrew

The FIRST thing is the capt. However, there should be a message on the DIC like "check gas cap".

Since the P0446 test specifically checks for "restricted or blocked EVAP vent path", probably a good idea to look there.

Again:

Oxygen454

Took a break and now I’m back at it.

I got a new scanner (Topdon ArtiDiag600S).

I was reviewing my notes for the P0446, the EVAP lines are clear, no blockages, front and rear valves replaced, and fuel tank cap is good. I realized that the tank pressure sensor was one I did not check.

I scanned the tank pressure sensor and it’s stuck at 1.76 psi. When I open the fuel cap, it doesn’t change. When I rev the engine, it doesn’t change.
I think I finally found the culprit.

The cat can’t seem to keep up and threw a P0420 as the O2 sensors are battling the maxed out fuel trims. I can see this on the wave length scans.

Now the question is, how hard is it to drop the tank? I hear it’s a bear to do. The guy had to compress the spring on the one side of the vehicle to have clearance for the tank.
I was thinking of cutting an access hole in the floor to get to the top of the tank. I had to do that to my 97 Camaro years ago.

Oldblue

Drop the exhaust and move it aside, I used a floor jack and a piece of plywood to support the tank and slowly lowered the tank. There’s more room if you place the jack stands out of the way and lift the rear axle up .

donbrew

Have you looked for a corrosion hole in the EVAP line next to the fuel line, under the insulation in front of the driver side rear wheel. Don't love run on sentences,\.

Oldblue

Look at those fuel line retainers and all along from engine to fuel tank. There’s photos in this

https://www.chevyhhr.net/forums/how-...follies-62310/