What are the probable causes of DTC P0449?

DTC P0449: Evaporative Emission (EVAP) Vent Solenoid Control Circuit

Circuit/System Description
An ignition voltage is supplied directly to the evaporative emission (EVAP) canister purge solenoid valve. The engine control module (ECM) grounds the EVAP canister purge solenoid valve control circuit through an internal switch called a driver. The ECM monitors the status of the driver. The EVAP canister purge solenoid valve is pulse width modulated (PWM). A scan tool will display the amount of ON time as a percentage.
Battery voltage is supplied to the EVAP canister solenoid valve. The ECM grounds the EVAP canister vent solenoid valve control circuit through an internal switch called a driver. The ECM monitors the status of the driver. A scan tool will display the commanded state of the EVAP canister vent solenoid valve as ON or OFF.

P0449
Ignition ON, engine OFF, command the EVAP vent solenoid ON and OFF with a scan tool.
Listen for a click when the valve operates. Verify that both the ON, and the OFF states are commanded.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing
Ignition OFF, disconnect the harness connector at the EVAP canister purge or vent solenoid valve.
Ignition ON, verify that a test lamp illuminates between the voltage supply circuit terminal A and ground.
? If the test lamp does not illuminate, test the voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and the voltage supply circuit fuse is open, test or replace the EVAP canister purge solenoid.
Connect a test lamp between the voltage supply circuit terminal A and the control circuit terminal B.
Command the EVAP canister purge solenoid valve to 50 percent with a scan tool, or the EVAP canister vent solenoid valve ON and OFF. The test lamp should respond to the command.
? If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.
? If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
If all circuits test normal, replace the appropriate solenoid valve.

This is how to test electrical circuit for the vent solenoid .

DTC P0449: Evaporative Emission (EVAP) Vent Solenoid Control Circuit , your vent solenoid is opened or the wiring circuit is . The vent solenoid is by the charcoal canister at the gas tank .
P0449 Battery voltage is supplied to the EVAP canister vent solenoid valve. The control module grounds the EVAP canister vent solenoid valve control circuit to close the valve by means of an internal switch called a driver. The scan tool displays the commanded state of the EVAP canister vent solenoid valve as ON or OFF. The control module monitors the status of the driver.

DTC P0446: Evaporative Emissions (EVAP) Vent System Performance
Circuit/System Description
This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path. The control module commands the EVAP canister purge solenoid valve Open and the EVAP canister vent solenoid valve Closed. This allows vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the EVAP canister purge solenoid valve Closed and the EVAP canister vent solenoid valve Open. The control module monitors the fuel tank pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near 0 inch H2O in a calibrated time, this DTC sets.
Diagnostic Aids
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An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP canister vent solenoid valve inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem.

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An EVAP canister, vent hose, or vent solenoid valve that has restricted flow may cause this DTC to set. Using a purge solenoid command with a scan tool will allow vacuum to be applied to the system instead of pressure. With the engine running, the EVAP canister vent solenoid valve open, and the EVAP canister purge solenoid valve commanded to 100 percent, the fuel tank vacuum should not increase to more than 5 inches H2O.

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An EVAP canister filter that is restricted can cause this DTC to set. Refer to Evaporative Emission Canister Replacement .

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Disconnecting one component at a time while the EVAP system is under flow will help to pinpoint a restriction in the system

Do you have a scan tool that reads data PID'S ?
Your FTP - fuel tank pressure sensor could be at fault !

Ignition ON and fuel cap removed, verify that the FTP sensor parameter is between 1.3-1.7 volts. ?‡'
If not within the specified range, go to the FTP sensor section in Circuit/System Testing.

1. Install the fuel cap.
2. With the engine running, the EVAP canister vent solenoid valve open, and the EVAP canister purge solenoid valve commanded to 100 percent, the fuel tank vacuum should not increase to more than 12 inches H2O.

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If the fuel tank vacuum is greater than the specified range, go to the restriction section in Circuit/System Testing.

If

P0449 Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction

Check for good connection, else replace

Here is the definition of the code and possible causes.

P0449 PONTIAC Description The Engine Control Module (ECM) monitors the Evaporative Emission System (EVAP) Vent Valve/Solenoid system wiring for opens or shorts.

When is the code detected?The Engine Control Module (ECM) has determined that a malfunction exists in the electrical circuit for the vent valve/solenoid in the evaporative emission control system.

Possible causes - Vacuum leaks, damaged hoses or improper routing
- EVAP system - Check fuel cap, canister, valves or components
- Faulty purge or vent solenoids
- Check connector and wiring
- Fuel saturated vapor canister
- Failed EVAP vent solenoid
Read more: http://engine-codes.com/p0449_pontiac.html#ixzz2M1YJd7DU

check engine light ison,autozone says code is P0449 this is whattheir ticket says:

The PCM has determined that a malfunction exists in the electrical circuit for the vent valve/solenoid in the evaporative emission control system.

Definition:
EVAP (Evaporative Emission System) purge/vent solenoid circuit condition

Explanation:
The solenoids and system wiring are monitored for opens or shorts

Probable Causes
1- Purge or vent solenoids defective
2- Check connevtor and wiring
3- Fuel saturated vapor canister
4- Failed EVAP vent solenoid

Your best bet take it to a qualified repair shop . It takes special tool's to diagnose evaporative emission system's .
DTC P0411 : Secondary Air Injection (AIR) System Incorrect Air Flow Detected
DTC P0449: Evaporative Emission (EVAP) Vent Solenoid Control Circuit
DTC P0455: Evaporative Emission (EVAP) System Large Leak

The PCM has determined that a malfunction exists in the electrical circuit for the vent valve/solenoid in the evaporative emission control system.

Definition:
EVAP (Evaporative Emission System) purge/vent solenoid circuit condition

Explanation:
The solenoids and system wiring are monitored for opens or shorts

Probable Causes
1- Purge or vent solenoids defective
2- Check connevtor and wiring
3- Fuel saturated vapor canister
4- Failed EVAP vent solenoid

sad to say that you miss on what you did, dtc P0449 was related to vent solenoid contol circuit, purge problem indicates P0443,, check the vent valve connectors supply voltage from the power distribution box, (fuse # 14-tcm/batt) and the other wire(almost white) to ecm C1 #61.

Hello. Your code indicates that your emission system is acting up. If you live in California, you might have a problem passing the next mandatory emmissions test. The PCM has determined that a malfunction exists in the electrical circuit for the vent valve/solenoid in the evaporative emission control system.

Definition:
EVAP (Evaporative Emission System) purge/vent solenoid circuit condition

Explanation:
The solenoids and system wiring are monitored for opens or shorts

Probable Causes
1- Purge or vent solenoids defective
2- Check connector and wiring
3- fuel, saturated vapor canister
4- Failed EVAP vent solenoid