P0449 Hyundai Sonata

Diagnose and fix P0449 Hyundai Sonata

A P0449 Hyundai Sonata is part of the evaporative emissions system. For more information on the EVAP system, see this post. The EVAP system consists of a charcoal canister, purge valve and vent or canister close valve. After filling with gas, the computer commands the purge valve and canister close valve to open. Engine vacuum pulls gas vapors out of the charcoal canister and fresh air enters through the canister close valve (CCV). The computer detects the richened mixture and can tell when the gas vapors have been fully removed from the canister. Then it commands the CCV valve to close. That applies a vacuum to the entire gas tank and EVAP system. Then it closes the purge valve and the computer monitors the vacuum state with the fuel tank pressure sensor. If there’s a leak in the system, it will set a trouble code.

What causes a P0449 Hyundai Sonata trouble code?

A P0449 Hyundai Sonata trouble code sets if the fuel tank pressure sensor reports a reading below 30-hPa (fuel tank pressure too low) or a fuel tank pressure sensor voltage less than 1.6v for at least 10-seconds. The computer sees this as a problem with not enough ventilation being allowed into the fuel tank. The shop manual states that the problem can be caused by a canister air filter contamination or a problem with the CCV valve or wiring harness.

How to diagnose a P0449 evaporative emission system vent valve

The CCV should be open to the atmosphere at all times when the engine is running. In effect, the CCV acts like a gas cap relief valve to allow air to replace the used gas. The ECU monitors the fuel tank pressure when the engine is running. So if pressure falls, indicating a vacuum condition, it sets the P0449 trouble code. A vacuum condition would occur as gasoline is being used up but no relief air is allowed into the system to replace the volume. The IGN switch provides power to the CCV, but the ECU only provides ground when it’s conducting an EVAP test.

So the CCV is OPEN to the atmosphere when it is DE-energized. You should be able to blow through the CCV when the IGN is in the OFF position. If you cannot blow through it, check the air filter for the CCV to see if it is plugged or restricted. If the valve is stuck shut. Replace the valve.

Where is the CCV?

The CCV is located near the charcoal canister.

©, 2017 Rick Muscoplat