The EVAP system is designed to capture and purge any fuel vapors in the fuel storage system. Instead of allowing these pollutants to leak into the atmosphere, the EVAP system stores the fuel vapors in a charcoal canister until they can be reintroduced into the combustion cycle.
When vehicle diagnostics detect a problem with the evaporative emission system vent control circuit, a P0449 code is logged by the car’s computer.
What Does the P0449 Code Mean?
Diagnostic trouble code (DTC) P0449 stands for “Evaporative System Vent Control Circuit Malfunction.” The code is set when the PCM detects that the actual state of the EVAP system vent valve does not match the desired state for a specific amount of time.
Code P0449 is a generic powertrain code which can be logged by vehicle diagnostics in various models manufactured from 1996 onwards. This means the code is supported by a variety of different makes and models, and as such, the process of diagnosis and repair may vary depending on each vehicle.
You can learn more information by reading our brief technical discussion about EVAP systems and code P0449.
What are the Possible Causes of the P0449 Code?
Code P0449 is typically logged when an electrical problem in the circuit or a mechanical problem with the vent valve interferes with its operation. However, there are a lot of other problems that can cause onboard diagnostics to trigger the P0449 code.
- Damaged or faulty evaporative system vent valve solenoid
- Connector pin fit issues
- Vent valve circuit problem (e.g., damaged wire or a poor connection), circuit malfunction, or faulty electrical connections
- PCM problems (e.g., software needs an update)
What are the Common Symptoms of the P0449 DTC?
The most common symptom of a P0449 is an illuminated check engine light.
Illuminated Check Engine Light
OBD-II code P0449 will trigger the Check Engine Light to illuminate. However, you will need to connect your vehicle to a scan tool to determine if there is a malfunction in the EVAP system vent control circuit.
How to Diagnose the P0449 Code
An accurate diagnosis is crucial in resolving the P0449 code. You can either leave the task to your mechanic or determine what triggered the code yourself. If you pick the latter, watch these video references to get an idea of what the diagnostic process involves:
How to Fix the P0449 Code
Like other OBD-II codes, the repair process for the P0449 code varies based on what caused the issue and, in some cases, the vehicle’s make and model. For instance, replacing the EVAP canister vent solenoid/valve is one of the most common confirmed fixes for P0449 in a Chevy Avalanche.
However, it may not work as well for vehicles from other automakers.
IIf you are certain of your automotive knowledge and DIY skills, you may resolve the issue yourself. Use online auto repair resources and guides or get an ALLDATA subscription to figure out the right way to resolve the issue.
Also, consult your owner’s manual before performing repairs to avoid accidentally worsening the issue with a fix that’s inappropriate for your vehicle.
More About EVAP Systems and P0449
Earlier EVAP canisters (pre OBD2) have an open vent that allows atmosphere to be drawn through the canister when the purge valve opens and delivers vacuum from the manifold to the canister. On those older platforms, EVAP purge only happened at off-idle. Typically there was a vacuum valve that was opened by “ported” vacuum when the engine was warm. Sometimes EGR and EVAP would operate concurrently.
That changed with the enhanced EVAP systems that were designed to detect leaks.
To determine if the EVAP system (fuel tank, canister, lines, etc.) has a vapor leak larger than .020 inch, the ECM/PCM energizes a normally open canister vent solenoid, which has a 12 volt feed and a ground trigger. When the vent is closed, the EVAP purge solenoid puts a very weak vacuum on the fuel system (including the canister) and traps it there while watching the fuel tank pressure sensor or a reed switch of some kind in a special assembly to determine if the weak vacuum is being lost.
Code P0449 focuses on the canister vent solenoid, which is constantly checked for an open circuit by the ECM/PCM.
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