Error Code P0449 means there’s a problem in the Evaporative Emission Control System Vent Valve or Solenoid Circuit malfunction.


Error Code p0449 is actually a generic powertrain code, which applies to all makes and models of vehicles from 1996 onward. However, since different manufacturers and models have different engine sructures, repair steps obviously vary between cars.

This error code means the PCM (Powertrain Control Module) or EMC (Engine Management Computer), or ECM (Engine Control Module) has detected a problem with the circuit that regulates the evaporative emission system vapor of the vent.

As the tank stores the fuel, fuel vapor goes out. When driving with the vent open, fuel vapor circulates into the engine intake manifold. Depending on the vehicle, it goes to the charcoal canister or to the atmosphere.

Common Symptoms

Many times, this error code doesn’t cause any adverse side effects that affect the drivability of the vehicle. Some of the common symptoms however, are:

  • Check Engine light is on
  • Obvious fuel odor from the released fuel vapor

Possible Causes

Some of the common causes of this error code include:

  • Damaged or defective fuel cap
  • Fuel cap is missing
  • Damaged or defective fuel tank
  • Faulty evaporative vent valve
  • Damaged, cracked fuel tank filler neck
  • Wire or circuit issue
  • Punctured or torn hoses of the Evaporative System
  • Faulty fuel tank sending unit gasket or seal
  • Damaged or split carbon canister
  • faulty PCM, EMC or ECM

Common Misdiagnoses

  • Fuel cap problem
  • Evaporative purge vale and vent valve

How to Check

The EVAP designed to perform two things: capture, store and expel raw fuel vapor that leaks from the Fuel Storage system and, run self-tests to determine the operation and vapor holding feature of the system. The second part is a very important task, as around 20% of air pollution produced by vehicles comes from faulty fuel storage systems of the vehicles.

There are a lot of ways to check for EVAP system leaks, most people test it after letting the vehicle sit overnight or throughout the initial startup after sitting overnight. The Powertrain Computer also tracks the operation of the EVAP system by reading changes in the O2 sensor voltages and short term fuel trim when the stored vapor is released or sent back to the combustion process. The results will give you a good idea of the overall mixture of the fuel (getting richer) as they’re being added to the system. The vehicle gets rid of it through acceleration, as it is where vehicles need more fuel.

Some vehicle’s PCM will trigger the error code if there’s an incorrect vacuum level during a leak test and the EVAP system has a valve that bypass and cuts off the fuel tank from the carbon canister-vent valve assembly. The vacuum is then monitored and measured by the Fuel Tank Pressure sensor. If the vacuum is too high for too long (aka stuck closed vent valve), or too short or non-existent (aka stuck open vent valve caused by a leak in the system or faulty sensor in fuel tank pressure).

The Powertrain Computer will then conduct the evaporative leak test.

There are also common ways to test the Evaporative System for possible problems.

  • Take note of both the code and freeze frame info for your baseline test, use it to very any repair.
  • Inspect all accessible components and hoses of the EVAP thoroughly, look for signs of degradation and damages.
  • Use a scan tool and take note of the readings of the Fuel Tank Pressure. Is the pressure sensor working properly? If it’s not, the system will assume that there is no vacuum or pressure being made during the EVAP test, when as a matter of fact, there is – the pressure sensor from the fuel tank just couldn’t read it. The Powertrain Computer depends on the Fuel Tank Pressure Sensor for the leak test data every time the monitor of the EVAP runs.
  • Check the fuel cap and see how it fits to the Filler Neck of the tank. Make sure the cap seal is cracked or dry. If it can’t hold pressure or seal tightly, then you need to get a new one.
  • Check how both the Purge Vale and Vent Vale holds vacuum for a particular amount of time – for 30 seconds at least. If one couldn’t work properly, the system won’t be able to hold the right level of vacuum.
  • If everything seems to be in good shape and is working properly, then your last resort is to conduct a smoke test in the whole EVAP system. This can easily expose all hidden leaks throughout the vehicle’s components. Pay attention to the Carbon Canister, the Fuel Tank and its Filler Neck, especially the Fuel Level Sending and Fuel Pump unit are found and sealed. Sometimes, when replacing the Fuel Pump, the seal will not be correctly installed. This often leads to small leaks. You will need to take off the back seats to thoroughly inspect the Fuel Tank for leaks.

How to Fix?

To fix this error code, check the fuses and see if there’s a fuse that powers the vent solenoid.

Look for chafed or rubbed-through wiring harness. Take a look at the wires and make sure they’re not shorted to each other, to power or ground.

Inspect the vent valve; look for cracks or any signs of damage.

Check the wires going to and from the PCM, EMC or ECM, and use a digital volt ohm meter (DVOM) for continuity.

If possible, use an advanced level scan tool, activate the valve while reading the ground and power at the connector. Use a bulb that is wired to both terminals. The scan tool will light up if both power and ground are in good working condition.

Also, use the DVOM to check vent’s resistance. Most of the time, resistance reading is low, which means you have to refer to the vehicle’s manual specs, or is possible, compare it to the new one. Values that are either too low or too high mean you need to replace it.

Lastly, take off the valve, you can access the pintle inside, and it may be just sticking from fuel residue. Clean it thoroughly, and retest to see if error code comes out again.

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