P0446 -What Does It Mean? (1999-2006 V8 Chevrolet Silverado, GMC Sierra)

A trouble code P0446: Evaporative Control System Vent Valve Performance usually points to a blocked EVAP vent solenoid that isn't able to draw fresh air into the EVAP carbon canister.

In this tutorial, I'll explain what this trouble code means. I'll also talk about some of the tests you can perform to find its cause.

RELATED CODES: P0449 -What Does It Mean? (1999-2006 V8 Chevrolet Silverado, GMC Sierra).

You can find this tutorial in Spanish here: Código P0446 ¿Qué Significa? (1999-2006 V8 Chevrolet Silverado, GMC Sierra) (at: autotecnico-online.com).

APPLIES TO: This tutorial, on the P0446 OBD II trouble code, applies to the following vehicles:

Chevrolet:

• 4.8L Chevrolet Silverado (1500, 2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• 5.3L Chevrolet Silverado (1500, 2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• 6.0L Chevrolet Silverado (2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006

GMC:

• 4.8L GMC Sierra (1500, 2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• 5.3L GMC Sierra (1500, 2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
• 6.0L GMC Sierra (2500): 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006

What Does Trouble Code P0446 Mean?

A trouble code P0446: Evaporative Control System Vent Valve Performance means that the EVAP vent solenoid is not allowing ambient air into the EVAP charcoal canister.

The EVAP vent solenoid's job is to allow ambient air into the charcoal canister so that fuel vapors can be purged from the activated carbon in the EVAP canister.

The EVAP vent solenoid also relieves EVAP system pressure that could cause fuel vapors to escape into the ambient air when the fuel tank cap is removed.

If there's any restriction that does not allow the EVAP vent solenoid to draw fresh air into the charcoal canister, EVAP system pressure will be high which will cause the fuel injection computer to set a P0446 trouble code.

Common Symptoms Of A P0446 Trouble Code

Generally, a problem with the EVAP system does not cause any drive-ability issues. Most folks will not feel any engine performance problems at all.

What you will experience will be:

• The check engine light will be illuminated in the instrument panel.
• Pressure in the gas tank when you remove the gas tank cap.
• Your Silverado (Sierra) fails the emissions test.
• Difficulty filling up the gas tank with fuel.

What Does The EVAP System Do?

The purpose of the evaporative emission control (EVAP) system is to capture the fuel tank vapors and prevent them from escaping into the ambient air (the atmosphere).

The EVAP system, on the 1999-2006 V8 Chevrolet Silverado (GMC Sierra), consists of following basic components:

• Gas cap.
• Fuel tank.
• EVAP vent solenoid.
• Fuel tank pressure sensor.
• Fuel pipes and hoses.
• Vapor lines.
• EVAP emission canister (charcoal canister).
• Purge lines.
• EVAP purge control solenoid.

NOTE: It's important that you consult your vehicle's emissions label and a repair manual to find out which components make up the EVAP system on your specific Chevy Silverado (GMC Sierra).

What Causes A P0446 Trouble Code?

In the majority of cases, this trouble code is the result of dirt restricting the fresh air intake of the EVAP vent solenoid.

How does it get clogged with dirt? This is due to the fact that the EVAP vent solenoid is located under the pickup (usually next to the fuel tank).

At this location, the EVAP vent solenoid is exposed to road dirt and dust, and becomes clogged/blocked with dirt.

How To Diagnose And Repair A P0446 Trouble Code

Troubleshooting and solving a trouble code P0446 involves locating the EVAP vent solenoid and making sure that it isn't blocked with dirt.

Although the EVAP vent solenoid itself could fail, it rarely does.

I recommend the following:

• Remove the vent solenoid and blow it out with compressed air.
• Remove the vent solenoid's air filter and blow it with compressed air.
• Check the EVAP canister vent hoses assembly for blockage.

For the 1999-2002 V8 Silverado (Sierra), you can find the EVAP solenoid bench-test and how to clean it here: How To Test The EVAP Vent Solenoid (1999-2002 V8 Chevrolet Silverado, GMC Sierra).

More Chevrolet Silverado (GMC Sierra) Tutorials

You can find a complete list of V8 Chevrolet Silverado (GMC Sierra) tutorials in this index:

• GM 4.8L, 5.3L, 6.0L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• Resistance Specifications Of The TAC Electronic Throttle Body.
• How To Test The GM Accelerator Pedal Position (APP) Sensor 2.
• How To Test The MAF Sensor (GM 4.8L, 5.3L, 6.0L, 8.1L).
• Blown Head Gasket Test (GM 4.8L, 5.3L, 6.0L).