How is fault code P0449 fixed?

A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training. 1. Read the code and the freeze frame data so you know what the car was doing when it logged, that tells you if it's an intermittent wiring fault or a hard failure 2. Pull the fuel cap and check the seal and that it clicks home properly, it's free and rules out the daft stuff first 3. Get under the back of the car and eyeball the vent valve, its connector, and the hoses for corrosion, road damage, or a connector full of muck 4. Measure resistance across the valve terminals with the ignition off, you're looking for roughly 20-40 ohms. Open circuit or a dead short tells you the valve is gone 5. Check for battery voltage at the valve feed with the ignition on to confirm the circuit is actually powered 6. Command the valve open and shut with a decent scan tool and listen for it clicking. No click with good power and a sound valve points at the PCM driver

Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction

Jump to the fix

Severity

Low

Can I keep driving?

Usually drivable; have it fixed at the first opportunity.

First step

A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training. 1. Read the code and the freeze frame data so you know what the car was doing when it logged, that tells you if it's an intermittent wiring fault or a hard failure 2. Pull the fuel cap and check the seal and that it clicks home properly, it's free and rules out the daft stuff first 3.

PPowertrain
0Generic code
4Emissions
49Sequence number

What does it mean?

OBD II fault code P0449 is defined as “Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction”, and is set when the PCM (Powertrain Control Module) detects that a part of the EVAP (Evaporative Emission Control System) is not working within design parameters. Note that this code refers specifically to the vent valve/solenoid control circuit.

Modern EVAP systems typically consist of the fuel tank, fuel filler cap, pressure and flow sensors, a charcoal canister, vent valve with a control solenoid, purge valve with a control solenoid, fuel and vacuum lines, fuel vapor hoses, and electrical wiring / connectors. The function of the EVAP system is to capture fuel vapors before they can escape into the atmosphere.

Fuel vapors are collected and passed through a charcoal canister in which the activated charcoal stores the vapors, before being passed to the inlet tract through a network of hoses to be burned as part of the air/fuel mixture when operational conditions allow this to happen.

The vent valve works in conjunction with the charcoal canister to achieve this, with the function of the vent valve being to allow atmospheric air to enter the EVAP system to help displace fuel vapors as the vapor is purged from the system to be combusted in the engine. On almost all applications, the vent valve is normally open, and the application of a 12-volt circuit current closes the valve when the PCM needs to pressurize the EVAP system to test for leaks.

Problems in the control circuit or a failure of the vent valve itself will store a trouble code and trigger the CHECK engine light. The image below shows the location of a vent valve in relation to the other major components in a typical EVAP system.

Symptoms

Likely causes

How to fix it

Codes From the Same System

All Fault Codes

Related Similar Codes

This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.