September I got the tighten fuel cap message (no check engine light) replaced cap (with factory replacement) still same. did my research evap canister was bad so I replaced the whole thing canister, purge valve, vent solenoid I changed it all cleaned lines went away until right before thanksgiving then same message with check engine light this time. Had code read says vent solenoid bad replaced for the second time no change. Tested all wires front to back all good. At this point I’m thinking leak in Evap system somewhere or is there anything else I can do or something else I can check to fix this
Do you have access to a bi-directional scan tool Jake? If so, it can command the vent solenoid on and you can listen for it to make sure it's working. Here's the test procedures from the shop manual for P0449:
P0449
1. Ignition ON, engine OFF, command the EVAP vent solenoid ON and OFF with a scan tool.
2. Listen for a click when the valve operates. Verify that both the ON, and the OFF states are commanded.
3. 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
1. Ignition OFF, disconnect the harness connector at the EVAP canister purge or vent solenoid valve.
2. 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.
3. Connect a test lamp between the voltage supply circuit terminal A and the control circuit terminal B.
4. 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.
5. If all circuits test normal, replace the appropriate solenoid valve.
One more thing, be sure to use OE or ACDelco parts, aftermarket does not always play well with factory computer system.
