4 Causes and Fixes P0449 Chevy Silverado or GMC Sierra – BackYardMechanic (2024)

If you have a Chevy Silverado or Sierra with a P0449 OBDII error code, there can be several causes and fixes.

Below are the most common symptoms, causes, and fixes.

What is a P0449 on a Chevy Silverado or GMC Sierra?

A P0449 Code is an “Evaporative System Vent Control Circuit Malfunction.”

This means the onboard computer (ECM) is seeing a problem in the EVAP system.

The most common cause is a bad gas cap, vapor canister, or vent solenoid.

Both fixes fall in the DIY category, but if in doubt, be sure to take your vehicle to a professional.

4 Causes and Fixes P0449 Code Chevy Silverado or Sierra

1. Gas Cap


If the gas cap is not seated all the way in place, it will cause an issue.

The gas cap may also have gone bad and is not sealing well and might need to be replaced.

Also, check for any dirt or grime that may be causing the cap to not make a good seal.

See Also
4 Causes and Fixes P0449 Chevy Silverado or GMC Sierra – BackYardMechanicP0449 – Meaning, Causes, Symptoms, & FixesDecoding P0449: Unveiling the Mystery of GMC Sierra's CodeDer ultimative Guide: Problemlösung für den GMC Sierra P0449 Code

There is rubber inside the cap that makes a seal when screwed into place. Examine the rubber to see if it is broken or old.

Often the cap can be replaced to rule it out a possible problem.

If a new cap is ordered, be sure to get the right one for your make and model, as they can differ.

2. Charcoal Canister or Vent Valve Solenoid


The vapor charcoal canister and the vent valve solenoid can cause EVAP issues and the P0449 error code.

A vent valve solenoid is usually located on or near the charcoal canister which is near the gas tank under the vehicle.

The charcoal canister mainly holds the gas vapors when the engine is off, and the vent valve is used by the ECM to test the EVAP system.

Common problems with the valve include sticking, staying open, and not closing.

Replacing a vent valve is a DIY job done by many backyard mechanics, but if in doubt, be sure to take your vehicle to a mechanic.

A new vent valve or the whole charcoal canister can be bought at an auto parts store or online on Amazon or eBay.

3. EVAP Leak

A leak in the EVAP system will cause issue and needs to be sealed to work properly.

Sometimes leaks can be visibly seen such as a cracked or loose hose while some leaks are harder to find.

See Also
GMC Sierra P0449 Code Diagnosis: EVAP System | Drivetrain Resource

Mechanics often use a smoke machine to find an EVAP leak which feeds smoke into the system and smoke escapes at the leaky location.

4. Bad Purge Valve

The purge valve is located in the engine compartment and will have two hoses and a wire harness going to it.

It opens to let gas vapor into the engine when it is running and closes to stop them from escaping when the engine is off.

While a bad purge valve will usually give another code, it can, in some cases, cause an issue.

Often if the solenoid is tapped on a few times, it will start working again for a short while, but if not, it will need to be replaced.

Summary
A Chevy Silverado or GMC Sierra with a P0449 OBDII error code is the ECM seeing a problem with the EVAP system.

This is usually a straightforward fix with either the gas cap is bad and not sealing the tank, or the vent solenoid has gone bad.

The first thing is to examine is the gas cap rubber seal; if it is bad, a replacement is best.

If the gas cap is good, the vent solenoid is likely bad.

Tapping on the solenoid can, in some cases, get it working again, but if not, it will need to be replaced.

Have you gotten a P0449 OBDII error code on a Chevy Silverado or GMC Sierra? Let us know your thoughts below.