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P0446 OBD2 Code in 2004 Buick Lesabre 3.8L - How to Diagnose EVAP Vent Valve Issue

Model: 2004 Buick Lesabre Fault Code: P0446 Posted: 2015-09-20 11:31

2004 Buick Lesabre 3.8L with 100,000 miles. The vehicle runs smoothly, but the fuel gauge is not working, making it difficult to track fuel mileage. I have already replaced the rusted fuel filler tube and cap, the corroded metal cage of the charcoal canister, and the front EVAP vent valve—using used parts for these components. Before performing a smoke test, I'm looking for additional diagnostic steps or information that could help identify the root cause of the P0446 code (EVAP Vent Circuit). Are there any specific checks I should perform to confirm whether the issue lies in the vent solenoid, wiring, or fuel tank pressure sensor?

Related fault codes
P0446
Comments (2)
Anonymous 2015-09-20 12:45

https://www.obd-codes.com/p0446 - This code relates to the EVAP Vent Circuit. Check if there is 12V power at the vent valve—this could indicate a blown fuse or wiring issue. Also, did you verify the condition of the used parts before installation? I would recommend checking for continuity and proper operation. Note: Fuel level may affect EVAP system testing; ensure the tank is not too full or empty when performing diagnostics.

Anonymous 2015-09-21 08:38

System Description: The P0446 code detects a restricted or blocked vent path in the evaporative emission (EVAP) system. The control module commands the EVAP canister purge solenoid to open and the vent solenoid to close, allowing vacuum to build in the EVAP system. Once a calibrated vacuum level is reached, it switches the purge solenoid to closed and opens the vent solenoid. It then monitors the fuel tank pressure (FTP) sensor for a drop in vacuum. If the vacuum doesn't decrease to near 0 inches H2O within a set time, the code activates. If you don’t have any fueling issues, it’s unlikely that the problem is due to a blocked vent hose or faulty canister. Possible causes include a stuck EVAP vent solenoid or a malfunctioning fuel tank pressure sensor—though the latter is rare. A bad vent solenoid is a common cause; check its resistance with an ohmmeter—open windings will show 'OL' (Open Loop). Do you have a digital multimeter? Also, determine whether this is a persistent (hard) fault or intermittent—this affects diagnostic approach.