If you want to know how to fix code P0446 and P0455, this article and video reviews the different components of the EVAP system, parts that can cause these problems, and different ways to diagnose what turned on the check engine light.
Why Is the Check Engine Light on for Codes P0446 & P0455?
When the car wants to engage the evaporative emission control (EVAP) system, it’ll send power and ground to the normally-open vents to close them.
The gas cap will block the fuel vapors from escaping the fuel tank, and they’ll travel to the charcoal canister instead of the atmosphere. The computer will open the purge valve and add vacuum to the system, and it’ll monitor the vacuum in the system to check for leaks.
Eventually the purge valve will close, and the computer will monitor how long the system can hold vacuum. If it can’t hold vacuum, you’ll get a check engine light.
How Do I Fix Code P0446 & P0455?
It’ll be hard to find the leak if it’s not one of these parts.
Steps to fix code P0446 & P0455
- Check the Gas Cap
Inspect the condition of the gas cap. Check the seal and make sure it isn’t broken or dry-rotted. Test the gas cap and make sure it’s tightening securely.
- Check the Purge Valve
The purge valve is also a likely cause of codes P0446 and P0455. On most vehicles, the purge valve will be at the front near the intake. It’ll have wires and hoses connected to it. To test if the valve is closing, you can take a vacuum pump, put vacuum on it, and the vacuum should stay. If it’s holding vacuum, the purge valve is working.
If you have a scan tool that’s capable, you can open the valve and check it with a scan tool and see if the reading falls to zero.
- Check the Vent Valve
The EVAP canister will be somewhere near the fuel tank. Near the EVAP charcoal canister is the vent valve. You can check the vent valve with a scan tool that’s capable of commanding it on and off so you can see if it’s working.
- Check the Gas Tank or Fuel Pump
For the remaining components, you could have a leak in the gas tank, like from an old rusty fuel pump.
- Test for Leaks with Soapy Water
You might be able to find a leak with soapy water that bubbles at the leak. It’ll be hard to pressurize the system, but on some vehicles the natural pressure of the fuel tank can cause bubbles in the soapy water.
- Test for Leaks with a Smoke Machine
A dealership or professional shop will probably use a smoke machine to find the leak, which is another way to test for leaks.
Shop Quality Auto Parts
What Is the EVAP System?
The EVAP system is part of emissions that prevents fuel vapors from entering the atmosphere.
What Parts Are in the EVAP System?
Components might be located in different places depending on the vehicle, but the basics of the system are the same
- Fuel tank, which has fuel vapors
- Gas cap
- EVAP charcoal canister
- EVAP vent valve
- Purge valve solenoid
The fuel tank might have a pressure sensor but it could also be in different place, like the fuel line or part of the vent valve.
Shop Parts
- Exterior, Body Parts & Mirrors
- Interior
- Engine & Engine Management
- Drivetrain
- Heating & Cooling
- Fuel & Emissions
Read More Tips
- Wheel Bearings & Wheel Hubs 101: What They Are And How They Fail
- What Is OBD II and How Does It Work?
- How to Winterize Your Truck
