Evap system code P0449
 

Purge valve is working, vent valve had broken wire at connector and repaired that but still getting code. I drive gravel roads daily and the vent valve was full of road dust. I cleaned it and the atmospheric vent line and verified the vent valve is operating correctly. Cap checks ok. I get a saturated pressure reading on the tank pressure sensor, so I'm going to look at that. With all the road dust could the carbon canister be plugged also?

Yes. They used to say to change the canister regularly, but not on the HHR.

P0449 point to the vent valve next to the gas tank.
It is actually the circuit that is monitored, not the pressure.
Which means the solenoid part of the valve is not operating correctly. It is a PWM signal, so a VOM won't tell you much.

Next question: how to test it?

I pulled the evap vent solenoid off the car and tested it with a 12vdc supply. If I remember correctly with no voltage applied the vent was open and I could blow through it. Applying 12 volts operated the solenoid closing the vent valve and I couldn't blow through it, (I might have the two states and related voltages ass-backwards). I'm confused about step #3, I'm assuming it is still referencing the vent solenoid, and I get terminal A, but what & where is terminal B?

Please note:
EVAP canister vent solenoid valve is under the car

EVAP canister purge solenoid valve is under the hood

The control signal is to ground via a PWM (Pulse Wave Modulation)

The connectors should be the same.

I use an Auto Enginuity pc adapter scan tool, but I didn't buy the enhanced package that allows me to input commands. However I've bench tested the vent solenoid and it works correctly. My fuel tank pressure sensor always reads high, would that also generate a P0449 code even though the vent opens to atmosphere or does an 06 HHR generate specific codes for an open or shorted fuel tank pressure sensor and I should continue to t-shoot the vent solenoid. Before I drop the tank I want to make sure I'm not missing something else. My next move is to monitor the signal with a VOM and the vent solenoid connected and run the engine long enough to generate and evap purge & vent condition.

What part of this sentence are you missing? The pressure has nothing to do with it, it is electrical somewhere between the ECM and the solenoid could be either side of the circuit.

As is shown in the diagram ; the PWM signal is the ground. The circuit is from B+ through fuse #64 underhood to terminal A on the vent solenoid to terminal B to pin #70 on the ECM then to ground via PWM (that means it varies state variably).

Here is some dangerous info. If you don't know what it means don't try. It is very technical, and way too much to get into here.

Your reader should be able to read mode $06, my $10 reader does.

My rational is the fuel tank pressure value is the part of the check to verify the system is performing correctly and there are no leaks. My scanner reads that value as fuel vapor pressure(or something like that) and that value is always saturated, even with the gas cap off. I realize I need to make sure the vent solenoid is getting pwm signal before I call that part of the evap system good. I get 5vdc to ground with the key switch on but I don't know if I'm getting a modulated signal to the vent solenoid. So based on your response if the pressure transducer was faulty I should get a code specific to its failure mode?

You should be able to monitor the EVAP states in real time, mine does. I have a ELM327 Bluetooth adapter to my laptop with the Scanmaster software, I think it's the free version. So, $10 works I assume $$$ would too. The "actuator" module (sending commands) will not work with my cars, I believe you need proprietary software.

On my software I choose either "live data meter" or "live data graph" or "live data grid" then the specific PID.