P0446 on 2005-2010 Pontiac G6: EVAP Vent Control Causes and Fixes

What's Unique About the 2005-2010 Pontiac G6

For GM vehicles of this era built on the Epsilon platform (including the G6, Chevy Malibu, and Saturn Aura), the P0446 code is strongly associated with a mechanical failure of the vent valve rather than a purely electrical issue. The valve and its associated hoses are located under the rear of the vehicle, typically behind the driver's side rear wheel well, making them highly susceptible to dirt, dust, and even spider webs, which leads to the valve sticking or the vent lines becoming clogged. Owners frequently report difficulty filling the gas tank as the primary symptom, which is a classic sign of a blocked EVAP vent path.

Symptoms You May Notice

• Check Engine Light is on
• Difficulty filling the fuel tank (gas pump nozzle clicks off repeatedly).
• Possible faint fuel odor near the rear of the vehicle.
• Remote start may be disabled while the Check Engine Light is active.

Most Likely Causes

1. Faulty EVAP Vent Valve/Solenoid 🔴 High Probability The vent solenoid is located under the vehicle near the charcoal canister, behind the driver's side rear wheel. Its exposed position allows road grime, moisture, and debris to enter the valve, causing it to mechanically stick closed and block the vent path.
   How to confirm: Locate the valve near the charcoal canister at the rear of the vehicle. With a scan tool, command the valve to open and close; you should hear a distinct click. If it doesn't click, test for 12V power and ground at the connector with the key on. If power is present 🎬 See how to test and replace the vent control valve but the valve doesn't actuate, it has failed. You can also remove it and try to blow through it; it should be normally open (air passes) and close when 12V is applied. A stuck valve will not allow air to pass.
   Typical fix: Replace the EVAP vent valve solenoid. This is a common DIY repair that involves raising the rear of the car, removing the driver's side rear wheel, and accessing the part through the wheel well.
   Est. part cost: $25-$60
2. Blocked or Clogged EVAP Vent Hose 🟡 Medium Probability The rubber and plastic hoses can become clogged with dirt, debris, or even spider webs, which is a known issue for this system. The blockage prevents air from flowing through the vent system, mimicking a stuck-closed valve.
   How to confirm: Visually inspect the hoses connected to the charcoal canister and vent solenoid for kinks, cracks, or obvious blockages. Remove the hoses and attempt to blow low-pressure compressed air through them to ensure they are clear.
   Typical fix: Clean out the blockage from the hose or replace the damaged section of the hose.
   Est. part cost: $10-$30
3. Failed or Clogged Charcoal Canister ⚪ Low Probability Habitually overfilling the fuel tank (topping off after the pump clicks) can force liquid fuel into the charcoal canister, saturating it and causing internal blockages. Over time, the charcoal pellets can also break down and clog the system.
   How to confirm: Disconnect the lines from the canister. If you see black charcoal pellets in the lines, the canister has failed and is the source of the blockage. A forum user with a P0446 and refueling issues on a similar GM platform confirmed a new canister was the ultimate fix after a new vent solenoid did not solve the problem.
   Typical fix: Replace the entire charcoal canister assembly. This is more expensive and typically only done if the vent solenoid replacement doesn't solve the issue or if there's clear evidence of canister failure.
   Est. part cost: $150-$350
4. Damaged Wiring or Connector ⚪ Low Probability
   How to confirm: Visually inspect the wiring harness and electrical connector going to the EVAP vent solenoid for any signs of corrosion, breaks, or loose pins. Use a multimeter to check for continuity and proper voltage (12V) at the connector with the key in the 'on' position.
   Typical fix: Repair the damaged section of wire or replace the connector pigtail.
   Est. part cost: $15-$30

Rare But Worth Checking

• Faulty Fuel Tank Pressure (FTP) Sensor: This is an uncommon cause for P0446 specifically, as a failing FTP sensor usually triggers its own set of codes (like P0452). However, a user on a GM forum reported chasing a P0446 code and only resolving it after replacing the FTP sensor. This is reinforced by NHTSA ODI #743096 for a similar Pontiac model, where a technician found the pressure sensor out of specs at 1.12 and replaced it to resolve the P0446.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0446 is present.
2. The most telling symptom is difficulty refueling. If the gas pump repeatedly clicks off, it strongly points to a vent path blockage.
🎬 Watch: How to fix a gas tank that won't fill
3. Visually inspect the EVAP vent solenoid, charcoal canister, and all attached hoses under the rear of the vehicle (behind the driver's side rear wheel). Look for obvious damage, cracks, or blockages from dirt/debris.
4. If you have a capable scan tool, command the EVAP vent solenoid to close. Listen for an audible click. Command it to open and listen again. No click suggests a bad solenoid or a wiring issue.
5. If the solenoid doesn't click, unplug it and check the connector for 12 volts with the ignition on. If voltage is present, the solenoid is faulty. If no voltage is present, inspect the wiring and fuses.
6. If the solenoid clicks, remove it and the attached hoses. Check the hoses and the solenoid's vent port for obstructions like dirt, debris, or insect nests/spider webs.
7. If the solenoid and hoses are clear, the charcoal canister may be clogged. Disconnect its lines and check for charcoal pellets, which indicates a failed canister.
8. If all components seem to work, a smoke test may be needed to find a restriction or hairline crack in the EVAP lines that isn't visually apparent.

Parts You'll Likely Need

• Vapor Canister Vent Solenoid (OEM #25932571 (Note: This part has been superseded, verify with VIN)) — This is the most common failure point for the P0446 code on the Pontiac G6. It gets stuck closed, blocking the vent path and causing refueling issues.
  Trusted brands: ACDelco (GM Genuine), Dorman (e.g., 911-030), Delphi
  OEM price range: $40-$70
  Aftermarket price range: $25-$60

Related Codes That Often Appear With This One

• P0455 — If a blockage in the vent system causes other components or lines to crack under pressure or vacuum, a large leak can develop, triggering P0455 alongside P0446.
• P0449 — This code also points to the EVAP vent valve/solenoid control circuit. While P0446 often indicates a restriction, P0449 is more specific to an electrical fault (open or short). They frequently appear together and point to the same component.

Technical Service Bulletins (TSBs) & Recalls

• GM TSB #02-06-04-037H: While officially for 1999-2009 Silverado/Sierra trucks, this bulletin details the exact failure pattern seen on the G6: 'Dirt and dust intrusion into the EVAP canister vent hose assembly, resulting in restricted air flow' causing P0446. It recommends replacing the vent valve and adding a remote filter box to prevent recurrence.

Platform-Specific Known Issues

• Debris Intrusion and TSB-Style Fix: While no TSB is specific to the G6 for P0446, GM has issued bulletins like #02-06-04-037H for trucks with the same issue: dust and debris entering the vent system and clogging the solenoid or canister. This is the core problem for the G6 due to the solenoid's exposed location. Some owners of other GM vehicles have adapted the TSB's fix by adding an inline filter or relocating the vent hose to a cleaner area, like higher in the wheel well, to prevent repeat failures.

Mechanic-Grade Diagnostic Values

• EVAP Vent Solenoid Resistance — expected: 20 to 50 Ohms. Failure: A reading outside of this range indicates a faulty solenoid coil.
• EVAP Vent Solenoid Connector Voltage — expected: 12V on the power wire (typically pink) with Key On, Engine Off.. Failure: No voltage suggests a wiring or fuse issue upstream from the solenoid.
• Fuel Tank Pressure (FTP) Sensor Voltage (at atmospheric pressure) — expected: Approximately 1.5 Volts. Failure: A voltage that is stuck high (e.g., 2.2V) or low, and does not change when the gas cap is removed, points to a failed sensor.

Scan Tool Commands That Help

• Tech2 / Professional Scan Tool: EVAP System Test (or Service Bay Test) — This function allows the technician to command the various EVAP solenoids (purge and vent) on and off to verify their mechanical and electrical operation. For P0446, a technician would command the vent solenoid closed and listen for a click, then command it open to confirm it's not stuck.

Wiring & Ground Locations

• G301 / G302 — In the rear of the vehicle, in the luggage compartment area. G301 is on the left side, G302 is on the right.. These are the primary body grounds in the rear of the car. The EVAP vent solenoid is located at the rear, and its circuit relies on a solid ground connection. A corroded or loose ground at one of these points could cause intermittent or failed operation of the vent solenoid, leading to a P0446 code.
• X413 — This is the body harness-to-fuel tank harness connector, located in the rear of the vehicle.. The wiring for the EVAP vent solenoid and fuel tank pressure sensor passes through this connector. Corrosion or a pushed-out pin at this location can interrupt the power or control signal to the vent solenoid, causing a P0446 fault.
• Vent Solenoid Connector — Directly on the EVAP vent solenoid, near the charcoal canister behind the driver's side rear wheel.. The two-pin connector provides power and ground control. The power wire is typically pink. The other wire is the control circuit grounded by the ECM. Checking for 12V on the power wire and a good ground path on the control wire (when commanded by a scan tool) is a key diagnostic step.

Real Owner Repair Stories

• GMTNation forum user (2006 GMC Envoy 5.3L (Similar GM EVAP system)) — P0446 code present, but no noticeable symptoms like refueling difficulty.
  ❌ Tried (didn't work) Replacing the EVAP vent valve solenoid., Performing a smoke test, which found no leaks.
  ✅ What actually fixed it The issue was not fully resolved by the user, but diagnosis pointed to a faulty Fuel Tank Pressure (FTP) sensor providing bad data. The user passed an emissions test by clearing the code and driving until monitors were ready, but the root cause was suspected to be the FTP sensor.
• YouTube video by 'FIX IT QUICK' (2009 Pontiac G6 3.5L) — Check Engine Light with codes P0446 and P0455.
  ❌ Tried (didn't work) The video directly diagnoses the issue without showing failed attempts.
  ✅ What actually fixed it The EVAP vent solenoid was confirmed to be faulty and was replaced. After replacement, the codes were cleared to complete the repair.

"I Checked Everything" — The Actual Cause

• In a detailed diagnostic case on a similar GM truck, a P0446 was present and a smoke test would have passed because there was no leak. The actual cause was a faulty Fuel Tank Pressure (FTP) sensor that was biased and stuck at a reading of 2.2 volts. The ECM interpreted this constant pressure reading (when it expected to see a change to atmospheric pressure) as a blocked vent path, setting the P0446 code. The FTP sensor was replaced, which resolved the issue.

Documented NHTSA Reports

• NHTSA ODI #11182132: An owner reported fuel leaking from the gas tank area accompanied by a P0446 code. The report mentions that while a recall existed for this model in that year range, the specific VIN was not included.
• NHTSA ODI #11124447: A report describes a crack in the fuel line above the fuel pump on top of the gas tank, resulting in a distinct gas smell and an OBD code P0446.

OEM Part Supersession History

• 10382105, 15750484, 22728634 → 25932571 — Part consolidation and design updates by GM over the years.
  Heads up: The current GM part number 25932571 is the correct service replacement for the earlier numbers. This is often sold under the ACDelco part number 214-2149.

Diagnostic Flowchart

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0451 — EVAP System Pressure Sensor Range/Performance - Appeared alongside P0446 in a 2009 Pontiac G6 owner's diagnostic report, indicating multiple potential EVAP system faults.
• P0101 — Mass Air Flow Sensor Circuit Range/Performance - Appeared as a companion code alongside P0446 in an owner's report.
• P0420 — Catalyst System Efficiency Below Threshold - Appeared as a companion code alongside P0446 in an owner's report.
• P0443 — Evaporative Emission Control System Purge Control Valve Circuit - Related to the purge valve, which owners sometimes mistakenly replace when trying to fix a P0446 code.
• P0455 — Evaporative Emission Control System Leak Detected (Gross Leak / No Flow) - Often related to a loose or faulty gas cap, which owners frequently (and often incorrectly) replace when diagnosing P0446.

Frequently Asked Questions