P0446 on 2007-2010 Pontiac G5: EVAP Vent Circuit Causes and Fixes

What's Unique About the 2007-2010 Pontiac G5

The Pontiac G5 and its twin, the Chevrolet Cobalt, are known for this specific issue. A General Motors technical bulletin (PIP3627) directly addresses P0446 and difficulty fueling. The cause is often a simple mechanical blockage, such as an insect nest (spiders are commonly cited) or debris clogging the EVAP canister vent pipe. Because the system's pressure monitoring is very sensitive, the pipe does not need to be fully restricted for the code to be set. This makes diagnosis relatively straightforward, often starting at the rear of the car near the charcoal canister.

Symptoms You May Notice

• Check Engine Light is on
• Difficulty filling the gas tank (fuel nozzle shuts off repeatedly).
• A faint fuel odor near the rear of the vehicle
• Release of vapor pressure (a 'whoosh' sound) when opening the gas cap.

Most Likely Causes

1. Faulty or Clogged EVAP Vent Solenoid 🔴 High Probability → Shop Vapor Canister The vent solenoid is located under the car near the rear wheel, making it susceptible to road debris, moisture, and dirt, which can cause it to stick closed or fail internally. Corrosion of the electrical connector is also common.
   How to confirm: Locate the vent solenoid on the charcoal canister (black box near the driver's side rear wheel). With a capable scan tool, command the valve to open and close; you should hear a click. Alternatively, remove the valve and apply 12V power to its terminals to see if the internal plunger moves. The valve is normally open, so you should be able to blow through it when no power is applied. Check for 12V at the pink wire in the connector with the key on. The other wire (often white) is the ground controlled by the PCM.
   Typical fix: Replace the EVAP vent solenoid. It is often attached directly to the charcoal canister and can be replaced separately.
   Est. part cost: $30-$70
2. Blocked EVAP Canister Vent Hose/Pipe 🟡 Medium Probability → Shop Vapor Canister A GM service bulletin (PIP3627) notes that the vent pipe is prone to being blocked by insect nests (like spiders or mud daubers) or other debris. The opening is an inviting place for spiders to build webs and egg sacs, causing a partial restriction.
   How to confirm: Locate the vent hose that runs from the charcoal canister towards the fuel filler neck area. Disconnect the hose from the canister and inspect it for blockages. Use compressed air to blow through the hose and check for debris. Even a small amount of debris can cause this code.
   Typical fix: Clear the obstruction from the hose using compressed air or a flexible brush. If the hose is damaged or brittle, it should be replaced.
   Est. part cost: $0-$30
3. Failed Charcoal Canister ⚪ Low Probability → Shop Vapor Canister Over-filling the fuel tank can force liquid gasoline into the charcoal canister, saturating the carbon pellets and causing an internal blockage that restricts airflow. The canister can also become clogged with dust if operated in very dusty environments, as noted in TSB 23-NA-073.
   How to confirm: After removing the canister, check if it feels unusually heavy or if charcoal pellets are coming out of the ports. If the vent solenoid and hoses are confirmed to be good but the restriction persists, the canister is the likely cause.
   Typical fix: Replace the entire charcoal canister assembly. The OEM part number is 19259321.
   Est. part cost: $150-$260

Rare But Worth Checking

• Failed Fuel Tank Pressure (FTP) Sensor: → Shop Fuel Tank While less common for this specific code, a faulty FTP sensor can send incorrect data to the computer, leading it to believe there is a vent problem. A technician video on a Cobalt showed an FTP sensor stuck reading positive pressure, which can mislead the PCM into setting a P0446 code even if the vent path is clear. A P0452 (FTP low voltage) code may also be present. In a cross-manufacturer reference, NHTSA ODI #743096 describes a case where a technician found the pressure sensor out of specs at 1.12 and replaced it to resolve a recurring P0446.
• Damaged Wiring or Connector: The wiring to the vent solenoid is under the vehicle and can be damaged by road debris or corrosion. One Cobalt owner reported that after replacing both solenoids, the actual problem was the white control wire for the vent solenoid had corroded and broken near the connector. Always inspect the harness for breaks, corrosion, or loose pins before replacing parts.

Diagnosis Steps

1. Verify the code with an OBD-II scanner.
2. Check for the most common symptom: Does the fuel pump nozzle click off when you try to fill the tank? If yes, a restriction is highly likely.
3. Visually inspect the EVAP system components at the rear of the vehicle, near the driver's side rear wheel. Look for the charcoal canister (a black plastic box), the attached vent solenoid, and associated hoses.
4. Inspect the vent hose running from the canister for any obvious blockages, kinks, or damage. Disconnect it and attempt to blow air through it to confirm it's clear. Pay close attention to the opening for spider webs.
5. Test the vent solenoid electrical circuit. Turn the ignition to 'ON' (engine off). Disconnect the solenoid and use a multimeter to check for battery voltage (~12V) at the pink wire in the harness connector.
6. Test the vent solenoid function. Use a scan tool to command it on/off and listen for a click. If you don't have a scan tool, remove the solenoid and apply 12V power to its terminals to test its function. The valve should click closed (it is normally open).
7. If the solenoid and hoses are good, inspect the charcoal canister for signs of fuel saturation (feeling heavy) or blockage by shaking it to see if loose carbon pellets are inside.
8. If all other components check out, the issue may be with the Fuel Tank Pressure (FTP) sensor. Use a scan tool to monitor the FTP sensor data; a sensor that is stuck reading pressure or vacuum when the system should be at atmospheric pressure is faulty.

Parts You'll Likely Need

• EVAP Vent Solenoid / Valve (OEM #ACDelco 214-2149) — This is the most common failure point for code P0446. It gets stuck closed or clogged, preventing the EVAP system from venting properly.
  Trusted brands: ACDelco, Dorman, Standard Motor Products (SMP)
  OEM price range: $50-$90
  Aftermarket price range: $30-$70
• EVAP Charcoal Canister (OEM #19259321) — This part is replaced if it becomes saturated with fuel from overfilling the tank or if it is internally blocked and restricting airflow.
  Trusted brands: ACDelco, Dorman
  OEM price range: $200-$300
  Aftermarket price range: $150-$260

Related Codes That Often Appear With This One

• P0449 — P0449 is an almost identical code for the EVAP Vent Solenoid Control Circuit, often pointing to an electrical fault rather than a restriction, but the components involved are the same. The diagnostic and repair steps are very similar.
• P0455 — This code indicates a large EVAP leak. It can sometimes appear with P0446 if the vent valve is stuck open, but P0446 on its own usually implies a restriction (stuck closed). TSBs mention them occurring together if the system is compromised by debris.
• P0442 — This code for a small EVAP leak can also be triggered by issues in the vent system, as noted in GM TSB 09-06-04-028D.

Technical Service Bulletins (TSBs) & Recalls

• PIP3627: Addresses P0446 and slow fuel fill due to restricted EVAP canister vent pipe, often from insect nests.
• 09-06-04-028D: Discusses P0446, P0442, P0455, and P0449 caused by dirt, dust, or water intrusion into the vent system.
• 23-NA-073: For vehicles in dusty environments, suggests a filter retrofit to prevent dust from clogging the EVAP canister and vent solenoid.

Platform-Specific Known Issues

• A GM Preliminary Information bulletin (PIP3627) was issued for the 2007 Pontiac G5 (and related Chevy Cobalt) for P0446 accompanied by a slow/difficult fuel fill condition, identifying the cause as a restricted EVAP canister vent pipe, often due to insect nests.
• TSB 09-06-04-028D notes that dirt, dust, or water intrusion can cause corrosion on the vent valve or clog the system, leading to codes P0446, P0449, and others.
• For vehicles operated in extremely dusty environments, TSB 23-NA-073 suggests that dust can clog the canister and vent solenoid, and provides a procedure for retrofitting an external filter to the vent hose as a customer-pay alteration. A user on a GM truck forum confirmed this exact scenario, finding the breather line and filter box packed solid with dirt.

Mechanic-Grade Diagnostic Values

• Fuel Tank Pressure (FTP) Sensor Voltage — expected: Approximately 1.5V with the gas cap off (atmospheric pressure). The acceptable range is generally 1.3V to 1.7V.. Failure: A reading stuck near 0V or 5V indicates a sensor or circuit fault. A reading that doesn't change when pulling a vacuum on the system also indicates a fault.
• EVAP Vent Solenoid Connector Voltage — expected: Approximately 12V (battery voltage) on the Pink wire with the ignition key in the 'ON' position.. Failure: No voltage suggests a wiring issue or a blown fuse (check the ECM/TRANS fuse).

Scan Tool Commands That Help

• Tech 2 / GDS2 / Capable Aftermarket Scanner: EVAP Service Bay Test (or EVAP Purge/Seal) — This is a guided diagnostic test to verify a repair or test the entire system's integrity. The tool commands the vent solenoid closed and the purge solenoid open to create a vacuum, then seals the system to see if the vacuum holds. This can confirm if a restriction (P0446) or a leak (other codes) is present without a smoke machine.
• Tech 2 / GDS2 / Capable Aftermarket Scanner: Vent Valve Solenoid Control — This is a simple bidirectional command to manually open and close the vent solenoid. It's used to listen for an audible 'click' from the solenoid to confirm it is mechanically responding to the ECM's command. This is the first step before performing more complex tests.

Wiring & Ground Locations

• EVAP Canister Vent Solenoid Connector — On the EVAP vent solenoid, attached to the charcoal canister, located under the rear of the vehicle near the driver's side wheel.. This 2-pin connector provides power and ground to the solenoid. The Pink wire should have ~12V with key-on, and the White wire is the ground control from the ECM. Corrosion or damage here will cause a P0446 or P0449.
• G402 — Center of the rear shelf, near the speaker.. This is a major ground point for several rear body components. While not directly tied to the EVAP solenoid circuit in most diagrams, a poor ground here can cause erratic behavior in nearby systems and is worth checking if electrical issues are suspected in the rear of the vehicle.
• G101 — On the left side of the engine compartment, under the coolant reservoir.. This is a primary engine ground. While the P0446 components are in the rear, the ECM that controls them is in the engine bay and relies on clean grounds like G101 to function correctly. An intermittent ground here could cause a variety of seemingly unrelated codes.

Real Owner Repair Stories

• YouTube channel 'Pine Hollow Auto Diagnostics' (2010 Chevrolet Cobalt 2.2L Manual) — Check Engine Light with codes P0446 (EVAP Vent System Performance) and P0452 (FTP Sensor Circuit Low Voltage).
  ❌ Tried (didn't work) Initial diagnosis focused on the vent valve and FTP sensor as separate issues.
  ✅ What actually fixed it A visual inspection revealed that the wiring harness going to the EVAP canister area had been rubbing against a sharp piece of the subframe. Multiple wires, including those for the FTP sensor and the vent solenoid, were chafed and shorting to ground. Repairing the damaged wires and securing the harness away from the sharp edge resolved both codes.

Documented NHTSA Reports

• NHTSA ODI #11182132 describes an owner reporting fuel leaking from the gas tank area accompanied by a P0446 code.
• An owner reported a distinct gas smell and a leak in the fuel line above the fuel pump on top of the gas tank, which triggered a P0446 code, as documented in NHTSA ODI #11124447.

OEM Part Supersession History

• 19177701 → 19259321 — Standard part update/revision by GM.
  Heads up: This part number is for vehicles with California Emissions (NE1). It is not compatible with Federal Emissions (FE1) vehicles, which use a different canister (PN 19259320).

Model Year Variations Within This Range

• 2007-2010: The most significant variation is not by year, but by the vehicle's original emissions certification. Vehicles with Federal Emissions (RPO code FE1) use a different charcoal canister and potentially different vent hose routing than vehicles with California Emissions (RPO code NE1). The parts are not interchangeable. Using the wrong canister will result in persistent EVAP codes.

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

• P0449 — EVAP Vent Valve Control Circuit. Frequently appears alongside P0446 on this platform due to dirt, dust, or water intrusion causing corrosion on the vent valve, as noted in TSB 09-06-04-028D.
• P0442 — EVAP System Small Leak Detected. Can be triggered by the same dirt and water intrusion issues affecting the vent system outlined in TSB 09-06-04-028D.
• P0455 — EVAP System Large Leak Detected. Often shares root causes with P0446, such as a vent valve that is stuck open due to debris or corrosion (TSB 09-06-04-028D).
• P0452 — Fuel Tank Pressure Sensor Circuit Low Voltage. A faulty FTP sensor can mimic EVAP flow issues and cause misdiagnosis of P0446, as the PCM relies on this sensor to monitor pressure changes.
• P0453 — Fuel Tank Pressure Sensor Circuit High Voltage. Related to the FTP sensor, which must be verified with a scan tool during P0446 diagnosis to ensure it isn't stuck reading pressure or vacuum.

Frequently Asked Questions