By Bojan Popic (Contact Me)
Last Updated 2023-11-21
Master Mechanical Engineer
| Code | Fault Location | Probable Cause |
|---|---|---|
| P0449 | Evaporative emission (EVAP) system, vent valve circuit malfunction (Buy Part On Amazon) |
We recommend Torque Pro
Table of Contents
- What Does Code P0449 Mean?
- Where is the P0449 sensor located?
- What are the common causes of code P0449?
- Get Help with P0449
What Does Code P0449 Mean?
NOTE: While this guide is specific to GMC vehicles, P0449 is a generic OBD2 diagnostic code. If your vehicle is not a GMC, check the generic version of this guide, as the following information will not apply to all vehicles. If you have a GMC with this code, we hope the detailed information below helps you. Please comment below the article with your year, model, engine type, and mileage, and we will respond and try to help.
The generic description for the P0449 trouble code is the Evaporative emission (EVAP) system, vent valve circuit malfunction. This code is set when the vehicle’s PCM detects an electrical issue with the said valve.
The EVAP is short for the Evaporative emission system, a pollution-control device that prevents the gas fumes inside the tank from venting into the atmosphere. Instead, it routes them into the engine’s intake manifold, where they are sucked into the cylinders and burned during combustion. The flow of exhaust gasses, however, should only happen when particular parameters – such as driving or engine running conditions – are met. This is why the EVAP has several PCM-activated valves that control its operation. One is the purge valve, which regulates the flow of gas fumes toward the engine. The other is the charcoal canister vent valve, whose job is to keep the fuel tank under atmospheric pressure. By doing so, it prevents pressure or vacuum buildups, which can be caused by temperature changes and fuel consumption. You can learn more about how the EVAP system works in this generic guide.
Where is the P0449 sensor located?
The vent valve is usually located near the charcoal canister, through which the gas fumes flow toward the engine. In most GMC SUVs that tend to suffer from P0449-related issues, both the valve and canister are fitted near the fuel tank. More specifically, you can find them on the chassis rear cross member, above the spare tire, which is recommended to be removed for better access. The photo below shows an approximate location in pickup trucks and truck-based SUVs, although this may differ slightly depending on the model.
What are the common causes of code P0449?
The faults that may set the P0449 trouble code in GMC vehicles don’t differ much from other makes. However, some issues are specific to this brand.
Malfunctioning vent valve
The vent valves, which have a higher-than-usual breakdown rate, are the most common failure point on most GMC models. They have a PCM-controlled solenoid inside, whose electrical circuit may fail. But before hastily replacing it, the valve’s operation may and should be tested first. This can be done by a diagnostic device capable of performing such testing or by hooking up the vent valve directly to the battery. The latter is done by connecting one of the valve’s pins to the positive terminal and the other to the negative. Once both wires are connected, you should hear an audible click from the vent valve.
GM developed an upgraded vent valve, which is not that failure-prone. But as it has a different connector, a wiring adapter is required, which is also available as an OEM part.
Blocked breather hose
The vent valve relieves the pressure or vacuum from the tank through a breather hose, which vents to the atmosphere. In certain conditions, dust, dirt, or moisture may find its way into the hose, obstructing the airflow. Yukon and Yukon XL models made between 2007 and 2010 are more prone to this issue. How this is checked and rectified is described in GM’s service bulletin 09-06-04-028D.
Dirt or corrosion in the fuse box
The wiring harness that leads to the vent valve has its own fuse in the fuse box within the engine bay. There are reported cases when dust and moisture have created corrosion buildups on the fuse seats, causing significant voltage drops. This has a similar effect as a broken vent valve or damaged wiring.
Help Us Help You
Please comment below describing your issue as well as the specifics of your vehicle (make, model, year, miles, and engine). To get a detailed, expedited response from a mechanic, please make a $9.99 donation via the payment button below.
